Add update datafeed endpoint

- Adds /_xpack/ml/datafeeds/{datafeed_id}/_update

Fixes elastic/elasticsearch#4954

Original commit: elastic/x-pack-elasticsearch@7a1887089d

elasticsearch/src/main/java/org/elasticsearch/xpack/ml/MlPlugin.java

@@ -62,6 +62,7 @@ import org.elasticsearch.xpack.ml.action.PutJobAction;
 import org.elasticsearch.xpack.ml.action.RevertModelSnapshotAction;
 import org.elasticsearch.xpack.ml.action.StartDatafeedAction;
 import org.elasticsearch.xpack.ml.action.StopDatafeedAction;
+import org.elasticsearch.xpack.ml.action.UpdateDatafeedAction;
 import org.elasticsearch.xpack.ml.action.UpdateJobAction;
 import org.elasticsearch.xpack.ml.action.UpdateModelSnapshotAction;
 import org.elasticsearch.xpack.ml.action.UpdateProcessAction;
@@ -92,6 +93,7 @@ import org.elasticsearch.xpack.ml.rest.datafeeds.RestGetDatafeedsAction;
 import org.elasticsearch.xpack.ml.rest.datafeeds.RestPutDatafeedAction;
 import org.elasticsearch.xpack.ml.rest.datafeeds.RestStartDatafeedAction;
 import org.elasticsearch.xpack.ml.rest.datafeeds.RestStopDatafeedAction;
+import org.elasticsearch.xpack.ml.rest.datafeeds.RestUpdateDatafeedAction;
 import org.elasticsearch.xpack.ml.rest.filter.RestDeleteFilterAction;
 import org.elasticsearch.xpack.ml.rest.filter.RestGetFiltersAction;
 import org.elasticsearch.xpack.ml.rest.filter.RestPutFilterAction;
@@ -293,6 +295,7 @@ public class MlPlugin extends Plugin implements ActionPlugin {
             new RestGetDatafeedsAction(settings, restController),
             new RestGetDatafeedStatsAction(settings, restController),
             new RestPutDatafeedAction(settings, restController),
+            new RestUpdateDatafeedAction(settings, restController),
             new RestDeleteDatafeedAction(settings, restController),
             new RestStartDatafeedAction(settings, restController),
             new RestStopDatafeedAction(settings, restController),
@@ -330,6 +333,7 @@ public class MlPlugin extends Plugin implements ActionPlugin {
                 new ActionHandler<>(GetDatafeedsAction.INSTANCE, GetDatafeedsAction.TransportAction.class),
                 new ActionHandler<>(GetDatafeedsStatsAction.INSTANCE, GetDatafeedsStatsAction.TransportAction.class),
                 new ActionHandler<>(PutDatafeedAction.INSTANCE, PutDatafeedAction.TransportAction.class),
+                new ActionHandler<>(UpdateDatafeedAction.INSTANCE, UpdateDatafeedAction.TransportAction.class),
                 new ActionHandler<>(DeleteDatafeedAction.INSTANCE, DeleteDatafeedAction.TransportAction.class),
                 new ActionHandler<>(StartDatafeedAction.INSTANCE, StartDatafeedAction.TransportAction.class),
                 new ActionHandler<>(StopDatafeedAction.INSTANCE, StopDatafeedAction.TransportAction.class),

elasticsearch/src/main/java/org/elasticsearch/xpack/ml/action/UpdateDatafeedAction.java

@@ -0,0 +1,179 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License;
+ * you may not use this file except in compliance with the Elastic License.
+ */
+package org.elasticsearch.xpack.ml.action;
+
+import org.elasticsearch.action.Action;
+import org.elasticsearch.action.ActionListener;
+import org.elasticsearch.action.ActionRequestValidationException;
+import org.elasticsearch.action.support.ActionFilters;
+import org.elasticsearch.action.support.master.AcknowledgedRequest;
+import org.elasticsearch.action.support.master.MasterNodeOperationRequestBuilder;
+import org.elasticsearch.action.support.master.TransportMasterNodeAction;
+import org.elasticsearch.client.ElasticsearchClient;
+import org.elasticsearch.cluster.AckedClusterStateUpdateTask;
+import org.elasticsearch.cluster.ClusterState;
+import org.elasticsearch.cluster.block.ClusterBlockException;
+import org.elasticsearch.cluster.block.ClusterBlockLevel;
+import org.elasticsearch.cluster.metadata.IndexNameExpressionResolver;
+import org.elasticsearch.cluster.metadata.MetaData;
+import org.elasticsearch.cluster.service.ClusterService;
+import org.elasticsearch.common.inject.Inject;
+import org.elasticsearch.common.io.stream.StreamInput;
+import org.elasticsearch.common.io.stream.StreamOutput;
+import org.elasticsearch.common.settings.Settings;
+import org.elasticsearch.common.xcontent.ToXContent;
+import org.elasticsearch.common.xcontent.XContentBuilder;
+import org.elasticsearch.common.xcontent.XContentParser;
+import org.elasticsearch.threadpool.ThreadPool;
+import org.elasticsearch.transport.TransportService;
+import org.elasticsearch.xpack.ml.datafeed.DatafeedConfig;
+import org.elasticsearch.xpack.ml.datafeed.DatafeedUpdate;
+import org.elasticsearch.xpack.ml.job.metadata.MlMetadata;
+import org.elasticsearch.xpack.persistent.PersistentTasksInProgress;
+
+import java.io.IOException;
+import java.util.Objects;
+
+public class UpdateDatafeedAction extends Action<UpdateDatafeedAction.Request, PutDatafeedAction.Response,
+        UpdateDatafeedAction.RequestBuilder> {
+
+    public static final UpdateDatafeedAction INSTANCE = new UpdateDatafeedAction();
+    public static final String NAME = "cluster:admin/ml/datafeeds/update";
+
+    private UpdateDatafeedAction() {
+        super(NAME);
+    }
+
+    @Override
+    public RequestBuilder newRequestBuilder(ElasticsearchClient client) {
+        return new RequestBuilder(client, this);
+    }
+
+    @Override
+    public PutDatafeedAction.Response newResponse() {
+        return new PutDatafeedAction.Response();
+    }
+
+    public static class Request extends AcknowledgedRequest<Request> implements ToXContent {
+
+        public static Request parseRequest(String datafeedId, XContentParser parser) {
+            DatafeedUpdate.Builder update = DatafeedUpdate.PARSER.apply(parser, null);
+            update.setId(datafeedId);
+            return new Request(update.build());
+        }
+
+        private DatafeedUpdate update;
+
+        public Request(DatafeedUpdate update) {
+            this.update = update;
+        }
+
+        Request() {
+        }
+
+        public DatafeedUpdate getUpdate() {
+            return update;
+        }
+
+        @Override
+        public ActionRequestValidationException validate() {
+            return null;
+        }
+
+        @Override
+        public void readFrom(StreamInput in) throws IOException {
+            super.readFrom(in);
+            update = new DatafeedUpdate(in);
+        }
+
+        @Override
+        public void writeTo(StreamOutput out) throws IOException {
+            super.writeTo(out);
+            update.writeTo(out);
+        }
+
+        @Override
+        public XContentBuilder toXContent(XContentBuilder builder, Params params) throws IOException {
+            update.toXContent(builder, params);
+            return builder;
+        }
+
+        @Override
+        public boolean equals(Object o) {
+            if (this == o) return true;
+            if (o == null || getClass() != o.getClass()) return false;
+            Request request = (Request) o;
+            return Objects.equals(update, request.update);
+        }
+
+        @Override
+        public int hashCode() {
+            return Objects.hash(update);
+        }
+    }
+
+    public static class RequestBuilder extends MasterNodeOperationRequestBuilder<Request, PutDatafeedAction.Response, RequestBuilder> {
+
+        public RequestBuilder(ElasticsearchClient client, UpdateDatafeedAction action) {
+            super(client, action, new Request());
+        }
+    }
+
+    public static class TransportAction extends TransportMasterNodeAction<Request, PutDatafeedAction.Response> {
+
+        @Inject
+        public TransportAction(Settings settings, TransportService transportService, ClusterService clusterService,
+                               ThreadPool threadPool, ActionFilters actionFilters,
+                               IndexNameExpressionResolver indexNameExpressionResolver) {
+            super(settings, UpdateDatafeedAction.NAME, transportService, clusterService, threadPool, actionFilters,
+                    indexNameExpressionResolver, Request::new);
+        }
+
+        @Override
+        protected String executor() {
+            return ThreadPool.Names.SAME;
+        }
+
+        @Override
+        protected PutDatafeedAction.Response newResponse() {
+            return new PutDatafeedAction.Response();
+        }
+
+        @Override
+        protected void masterOperation(Request request, ClusterState state, ActionListener<PutDatafeedAction.Response> listener)
+                throws Exception {
+            clusterService.submitStateUpdateTask("update-datafeed-" + request.getUpdate().getId(),
+                    new AckedClusterStateUpdateTask<PutDatafeedAction.Response>(request, listener) {
+                        private DatafeedConfig updatedDatafeed;
+
+                        @Override
+                        protected PutDatafeedAction.Response newResponse(boolean acknowledged) {
+                            if (acknowledged) {
+                                logger.info("Updated datafeed [{}]", request.getUpdate().getId());
+                            }
+                            return new PutDatafeedAction.Response(acknowledged, updatedDatafeed);
+                        }
+
+                        @Override
+                        public ClusterState execute(ClusterState currentState) throws Exception {
+                            DatafeedUpdate update = request.getUpdate();
+                            MlMetadata currentMetadata = state.getMetaData().custom(MlMetadata.TYPE);
+                            PersistentTasksInProgress persistentTasksInProgress = state.custom(PersistentTasksInProgress.TYPE);
+                            MlMetadata newMetadata = new MlMetadata.Builder(currentMetadata)
+                                    .updateDatafeed(update, persistentTasksInProgress).build();
+                            updatedDatafeed = newMetadata.getDatafeed(update.getId());
+                            return ClusterState.builder(currentState).metaData(
+                                    MetaData.builder(currentState.getMetaData()).putCustom(MlMetadata.TYPE, newMetadata).build()).build();
+                        }
+                    });
+        }
+
+        @Override
+        protected ClusterBlockException checkBlock(Request request, ClusterState state) {
+            return state.blocks().globalBlockedException(ClusterBlockLevel.METADATA_WRITE);
+        }
+    }
+}

elasticsearch/src/main/java/org/elasticsearch/xpack/ml/datafeed/DatafeedConfig.java

@@ -177,22 +177,10 @@ public class DatafeedConfig extends AbstractDiffable<DatafeedConfig> implements
         return frequency;
     }
 
-    /**
-     * For the ELASTICSEARCH data source only, one or more indexes to search for
-     * input data.
-     *
-     * @return The indexes to search, or <code>null</code> if not set.
-     */
     public List<String> getIndexes() {
         return indexes;
     }
 
-    /**
-     * For the ELASTICSEARCH data source only, one or more types to search for
-     * input data.
-     *
-     * @return The types to search, or <code>null</code> if not set.
-     */
     public List<String> getTypes() {
         return types;
     }
@@ -213,6 +201,13 @@ public class DatafeedConfig extends AbstractDiffable<DatafeedConfig> implements
         return aggregations;
     }
 
+    /**
+     * @return {@code true} when there are non-empty aggregations, {@code false} otherwise
+     */
+    public boolean hasAggregations() {
+        return aggregations != null && aggregations.count() > 0;
+    }
+
     public List<SearchSourceBuilder.ScriptField> getScriptFields() {
         return scriptFields == null ? Collections.emptyList() : scriptFields;
     }

elasticsearch/src/main/java/org/elasticsearch/xpack/ml/datafeed/DatafeedJobRunner.java

@@ -164,7 +164,7 @@ public class DatafeedJobRunner extends AbstractComponent {
     }
 
     DataExtractorFactory createDataExtractorFactory(DatafeedConfig datafeedConfig, Job job) {
-        boolean isScrollSearch = datafeedConfig.getAggregations() == null;
+        boolean isScrollSearch = datafeedConfig.hasAggregations() == false;
         DataExtractorFactory dataExtractorFactory = isScrollSearch ? new ScrollDataExtractorFactory(client, datafeedConfig, job)
                 : new AggregationDataExtractorFactory(client, datafeedConfig, job);
         ChunkingConfig chunkingConfig = datafeedConfig.getChunkingConfig();

elasticsearch/src/main/java/org/elasticsearch/xpack/ml/datafeed/DatafeedJobValidator.java

@@ -23,7 +23,7 @@ public final class DatafeedJobValidator {
         if (analysisConfig.getLatency() != null && analysisConfig.getLatency() > 0) {
             throw new IllegalArgumentException(Messages.getMessage(Messages.DATAFEED_DOES_NOT_SUPPORT_JOB_WITH_LATENCY));
         }
-        if (datafeedConfig.getAggregations() != null && !DatafeedConfig.DOC_COUNT.equals(analysisConfig.getSummaryCountFieldName())) {
+        if (datafeedConfig.hasAggregations() && !DatafeedConfig.DOC_COUNT.equals(analysisConfig.getSummaryCountFieldName())) {
             throw new IllegalArgumentException(
                     Messages.getMessage(Messages.DATAFEED_AGGREGATIONS_REQUIRES_JOB_WITH_SUMMARY_COUNT_FIELD, DatafeedConfig.DOC_COUNT));
         }

elasticsearch/src/main/java/org/elasticsearch/xpack/ml/datafeed/DatafeedUpdate.java

@@ -0,0 +1,371 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License;
+ * you may not use this file except in compliance with the Elastic License.
+ */
+package org.elasticsearch.xpack.ml.datafeed;
+
+import org.elasticsearch.common.ParseField;
+import org.elasticsearch.common.Strings;
+import org.elasticsearch.common.io.stream.StreamInput;
+import org.elasticsearch.common.io.stream.StreamOutput;
+import org.elasticsearch.common.io.stream.Writeable;
+import org.elasticsearch.common.xcontent.ObjectParser;
+import org.elasticsearch.common.xcontent.ToXContent;
+import org.elasticsearch.common.xcontent.XContentBuilder;
+import org.elasticsearch.common.xcontent.XContentParser;
+import org.elasticsearch.index.query.QueryBuilder;
+import org.elasticsearch.index.query.QueryParseContext;
+import org.elasticsearch.search.aggregations.AggregatorFactories;
+import org.elasticsearch.search.builder.SearchSourceBuilder;
+import org.elasticsearch.xpack.ml.job.config.Job;
+import org.elasticsearch.xpack.ml.utils.ExceptionsHelper;
+
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.Comparator;
+import java.util.List;
+import java.util.Objects;
+
+/**
+ * A datafeed update contains partial properties to update a {@link DatafeedConfig}.
+ * The main difference between this class and {@link DatafeedConfig} is that here all
+ * fields are nullable.
+ */
+public class DatafeedUpdate implements Writeable, ToXContent {
+
+    public static final ObjectParser<Builder, Void> PARSER = new ObjectParser<>("datafeed_update", Builder::new);
+
+    static {
+        PARSER.declareString(Builder::setId, DatafeedConfig.ID);
+        PARSER.declareString(Builder::setJobId, Job.ID);
+        PARSER.declareStringArray(Builder::setIndexes, DatafeedConfig.INDEXES);
+        PARSER.declareStringArray(Builder::setTypes, DatafeedConfig.TYPES);
+        PARSER.declareLong(Builder::setQueryDelay, DatafeedConfig.QUERY_DELAY);
+        PARSER.declareLong(Builder::setFrequency, DatafeedConfig.FREQUENCY);
+        PARSER.declareObject(Builder::setQuery,
+                (p, c) -> new QueryParseContext(p).parseInnerQueryBuilder(), DatafeedConfig.QUERY);
+        PARSER.declareObject(Builder::setAggregations, (p, c) -> AggregatorFactories.parseAggregators(new QueryParseContext(p)),
+                DatafeedConfig.AGGREGATIONS);
+        PARSER.declareObject(Builder::setAggregations,(p, c) -> AggregatorFactories.parseAggregators(new QueryParseContext(p)),
+                DatafeedConfig.AGGS);
+        PARSER.declareObject(Builder::setScriptFields, (p, c) -> {
+                List<SearchSourceBuilder.ScriptField> parsedScriptFields = new ArrayList<>();
+                while (p.nextToken() != XContentParser.Token.END_OBJECT) {
+                    parsedScriptFields.add(new SearchSourceBuilder.ScriptField(new QueryParseContext(p)));
+            }
+            parsedScriptFields.sort(Comparator.comparing(SearchSourceBuilder.ScriptField::fieldName));
+            return parsedScriptFields;
+        }, DatafeedConfig.SCRIPT_FIELDS);
+        PARSER.declareInt(Builder::setScrollSize, DatafeedConfig.SCROLL_SIZE);
+        PARSER.declareBoolean(Builder::setSource, DatafeedConfig.SOURCE);
+        PARSER.declareObject(Builder::setChunkingConfig, ChunkingConfig.PARSER, DatafeedConfig.CHUNKING_CONFIG);
+    }
+
+    private final String id;
+    private final String jobId;
+    private final Long queryDelay;
+    private final Long frequency;
+    private final List<String> indexes;
+    private final List<String> types;
+    private final QueryBuilder query;
+    private final AggregatorFactories.Builder aggregations;
+    private final List<SearchSourceBuilder.ScriptField> scriptFields;
+    private final Integer scrollSize;
+    private final Boolean source;
+    private final ChunkingConfig chunkingConfig;
+
+    private DatafeedUpdate(String id, String jobId, Long queryDelay, Long frequency, List<String> indexes, List<String> types,
+                           QueryBuilder query, AggregatorFactories.Builder aggregations, List<SearchSourceBuilder.ScriptField> scriptFields,
+                           Integer scrollSize, Boolean source, ChunkingConfig chunkingConfig) {
+        this.id = id;
+        this.jobId = jobId;
+        this.queryDelay = queryDelay;
+        this.frequency = frequency;
+        this.indexes = indexes;
+        this.types = types;
+        this.query = query;
+        this.aggregations = aggregations;
+        this.scriptFields = scriptFields;
+        this.scrollSize = scrollSize;
+        this.source = source;
+        this.chunkingConfig = chunkingConfig;
+    }
+
+    public DatafeedUpdate(StreamInput in) throws IOException {
+        this.id = in.readString();
+        this.jobId = in.readOptionalString();
+        this.queryDelay = in.readOptionalLong();
+        this.frequency = in.readOptionalLong();
+        if (in.readBoolean()) {
+            this.indexes = in.readList(StreamInput::readString);
+        } else {
+            this.indexes = null;
+        }
+        if (in.readBoolean()) {
+            this.types = in.readList(StreamInput::readString);
+        } else {
+            this.types = null;
+        }
+        this.query = in.readOptionalNamedWriteable(QueryBuilder.class);
+        this.aggregations = in.readOptionalWriteable(AggregatorFactories.Builder::new);
+        if (in.readBoolean()) {
+            this.scriptFields = in.readList(SearchSourceBuilder.ScriptField::new);
+        } else {
+            this.scriptFields = null;
+        }
+        this.scrollSize = in.readOptionalVInt();
+        this.source = in.readOptionalBoolean();
+        this.chunkingConfig = in.readOptionalWriteable(ChunkingConfig::new);
+    }
+
+    /**
+     * Get the id of the datafeed to update
+     */
+    public String getId() {
+        return id;
+    }
+
+    @Override
+    public void writeTo(StreamOutput out) throws IOException {
+        out.writeString(id);
+        out.writeOptionalString(jobId);
+        out.writeOptionalLong(queryDelay);
+        out.writeOptionalLong(frequency);
+        if (indexes != null) {
+            out.writeBoolean(true);
+            out.writeStringList(indexes);
+        } else {
+            out.writeBoolean(false);
+        }
+        if (types != null) {
+            out.writeBoolean(true);
+            out.writeStringList(types);
+        } else {
+            out.writeBoolean(false);
+        }
+        out.writeOptionalNamedWriteable(query);
+        out.writeOptionalWriteable(aggregations);
+        if (scriptFields != null) {
+            out.writeBoolean(true);
+            out.writeList(scriptFields);
+        } else {
+            out.writeBoolean(false);
+        }
+        out.writeOptionalVInt(scrollSize);
+        out.writeOptionalBoolean(source);
+        out.writeOptionalWriteable(chunkingConfig);
+    }
+
+    @Override
+    public XContentBuilder toXContent(XContentBuilder builder, Params params) throws IOException {
+        builder.startObject();
+        builder.field(DatafeedConfig.ID.getPreferredName(), id);
+        addOptionalField(builder, Job.ID, jobId);
+        addOptionalField(builder, DatafeedConfig.QUERY_DELAY, queryDelay);
+        addOptionalField(builder, DatafeedConfig.FREQUENCY, frequency);
+        addOptionalField(builder, DatafeedConfig.INDEXES, indexes);
+        addOptionalField(builder, DatafeedConfig.TYPES, types);
+        addOptionalField(builder, DatafeedConfig.QUERY, query);
+        addOptionalField(builder, DatafeedConfig.AGGREGATIONS, aggregations);
+        if (scriptFields != null) {
+            builder.startObject(DatafeedConfig.SCRIPT_FIELDS.getPreferredName());
+            for (SearchSourceBuilder.ScriptField scriptField : scriptFields) {
+                scriptField.toXContent(builder, params);
+            }
+            builder.endObject();
+        }
+        addOptionalField(builder, DatafeedConfig.SCROLL_SIZE, scrollSize);
+        addOptionalField(builder, DatafeedConfig.SOURCE, source);
+        addOptionalField(builder, DatafeedConfig.CHUNKING_CONFIG, chunkingConfig);
+        builder.endObject();
+        return builder;
+    }
+
+    private void addOptionalField(XContentBuilder builder, ParseField field, Object value) throws IOException {
+        if (value != null) {
+            builder.field(field.getPreferredName(), value);
+        }
+    }
+
+    /**
+     * Applies the update to the given {@link DatafeedConfig}
+     * @return a new {@link DatafeedConfig} that contains the update
+     */
+    public DatafeedConfig apply(DatafeedConfig datafeedConfig) {
+        if (id.equals(datafeedConfig.getId()) == false) {
+            throw new IllegalArgumentException("Cannot apply update to datafeedConfig with different id");
+        }
+
+        DatafeedConfig.Builder builder = new DatafeedConfig.Builder(datafeedConfig);
+        if (jobId != null) {
+            builder.setJobId(jobId);
+        }
+        if (queryDelay != null) {
+            builder.setQueryDelay(queryDelay);
+        }
+        if (frequency != null) {
+            builder.setFrequency(frequency);
+        }
+        if (indexes != null) {
+            builder.setIndexes(indexes);
+        }
+        if (types != null) {
+            builder.setTypes(types);
+        }
+        if (query != null) {
+            builder.setQuery(query);
+        }
+        if (aggregations != null) {
+            builder.setAggregations(aggregations);
+        }
+        if (scriptFields != null) {
+            builder.setScriptFields(scriptFields);
+        }
+        if (scrollSize != null) {
+            builder.setScrollSize(scrollSize);
+        }
+        if (source != null) {
+            builder.setSource(source);
+        }
+        if (chunkingConfig != null) {
+            builder.setChunkingConfig(chunkingConfig);
+        }
+        return builder.build();
+    }
+
+    /**
+     * The lists of indexes and types are compared for equality but they are not
+     * sorted first so this test could fail simply because the indexes and types
+     * lists are in different orders.
+     */
+    @Override
+    public boolean equals(Object other) {
+        if (this == other) {
+            return true;
+        }
+
+        if (other instanceof DatafeedUpdate == false) {
+            return false;
+        }
+
+        DatafeedUpdate that = (DatafeedUpdate) other;
+
+        return Objects.equals(this.id, that.id)
+                && Objects.equals(this.jobId, that.jobId)
+                && Objects.equals(this.frequency, that.frequency)
+                && Objects.equals(this.queryDelay, that.queryDelay)
+                && Objects.equals(this.indexes, that.indexes)
+                && Objects.equals(this.types, that.types)
+                && Objects.equals(this.query, that.query)
+                && Objects.equals(this.scrollSize, that.scrollSize)
+                && Objects.equals(this.aggregations, that.aggregations)
+                && Objects.equals(this.scriptFields, that.scriptFields)
+                && Objects.equals(this.source, that.source)
+                && Objects.equals(this.chunkingConfig, that.chunkingConfig);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(id, jobId, frequency, queryDelay, indexes, types, query, scrollSize, aggregations, scriptFields, source,
+                chunkingConfig);
+    }
+
+    @Override
+    public String toString() {
+        return Strings.toString(this);
+    }
+
+    public static class Builder {
+
+        private String id;
+        private String jobId;
+        private Long queryDelay;
+        private Long frequency;
+        private List<String> indexes;
+        private List<String> types;
+        private QueryBuilder query;
+        private AggregatorFactories.Builder aggregations;
+        private List<SearchSourceBuilder.ScriptField> scriptFields;
+        private Integer scrollSize;
+        private Boolean source;
+        private ChunkingConfig chunkingConfig;
+
+        public Builder() {
+        }
+
+        public Builder(String id) {
+            this.id = ExceptionsHelper.requireNonNull(id, DatafeedConfig.ID.getPreferredName());
+        }
+
+        public Builder(DatafeedUpdate config) {
+            this.id = config.id;
+            this.jobId = config.jobId;
+            this.queryDelay = config.queryDelay;
+            this.frequency = config.frequency;
+            this.indexes = config.indexes;
+            this.types = config.types;
+            this.query = config.query;
+            this.aggregations = config.aggregations;
+            this.scriptFields = config.scriptFields;
+            this.scrollSize = config.scrollSize;
+            this.source = config.source;
+            this.chunkingConfig = config.chunkingConfig;
+        }
+
+        public void setId(String datafeedId) {
+            id = ExceptionsHelper.requireNonNull(datafeedId, DatafeedConfig.ID.getPreferredName());
+        }
+
+        public void setJobId(String jobId) {
+            this.jobId = jobId;
+        }
+
+        public void setIndexes(List<String> indexes) {
+            this.indexes = indexes;
+        }
+
+        public void setTypes(List<String> types) {
+            this.types = types;
+        }
+
+        public void setQueryDelay(long queryDelay) {
+            this.queryDelay = queryDelay;
+        }
+
+        public void setFrequency(long frequency) {
+            this.frequency = frequency;
+        }
+
+        public void setQuery(QueryBuilder query) {
+            this.query = query;
+        }
+
+        public void setAggregations(AggregatorFactories.Builder aggregations) {
+            this.aggregations = aggregations;
+        }
+
+        public void setScriptFields(List<SearchSourceBuilder.ScriptField> scriptFields) {
+            List<SearchSourceBuilder.ScriptField> sorted = new ArrayList<>(scriptFields);
+            sorted.sort(Comparator.comparing(SearchSourceBuilder.ScriptField::fieldName));
+            this.scriptFields = sorted;
+        }
+
+        public void setScrollSize(int scrollSize) {
+            this.scrollSize = scrollSize;
+        }
+
+        public void setSource(boolean enabled) {
+            this.source = enabled;
+        }
+
+        public void setChunkingConfig(ChunkingConfig chunkingConfig) {
+            this.chunkingConfig = chunkingConfig;
+        }
+
+        public DatafeedUpdate build() {
+            return new DatafeedUpdate(id, jobId, queryDelay, frequency, indexes, types, query, aggregations, scriptFields, scrollSize,
+                    source, chunkingConfig);
+        }
+    }
+}

elasticsearch/src/main/java/org/elasticsearch/xpack/ml/job/metadata/MlMetadata.java

@@ -26,6 +26,7 @@ import org.elasticsearch.xpack.ml.action.StartDatafeedAction;
 import org.elasticsearch.xpack.ml.datafeed.DatafeedConfig;
 import org.elasticsearch.xpack.ml.datafeed.DatafeedJobValidator;
 import org.elasticsearch.xpack.ml.datafeed.DatafeedState;
+import org.elasticsearch.xpack.ml.datafeed.DatafeedUpdate;
 import org.elasticsearch.xpack.ml.job.config.Job;
 import org.elasticsearch.xpack.ml.job.config.JobState;
 import org.elasticsearch.xpack.ml.job.messages.Messages;
@@ -43,6 +44,7 @@ import java.util.Optional;
 import java.util.SortedMap;
 import java.util.TreeMap;
 import java.util.function.Predicate;
+import java.util.function.Supplier;
 
 public class MlMetadata implements MetaData.Custom {
 
@@ -254,6 +256,14 @@ public class MlMetadata implements MetaData.Custom {
                 throw new ResourceAlreadyExistsException("A datafeed with id [" + datafeedConfig.getId() + "] already exists");
             }
             String jobId = datafeedConfig.getJobId();
+            checkJobIsAvailableForDatafeed(jobId);
+            Job job = jobs.get(jobId);
+            DatafeedJobValidator.validate(datafeedConfig, job);
+            datafeeds.put(datafeedConfig.getId(), datafeedConfig);
+            return this;
+        }
+
+        private void checkJobIsAvailableForDatafeed(String jobId) {
             Job job = jobs.get(jobId);
             if (job == null) {
                 throw ExceptionsHelper.missingJobException(jobId);
@@ -263,9 +273,23 @@ public class MlMetadata implements MetaData.Custom {
                 throw ExceptionsHelper.conflictStatusException("A datafeed [" + existingDatafeed.get().getId()
                         + "] already exists for job [" + jobId + "]");
             }
-            DatafeedJobValidator.validate(datafeedConfig, job);
+        }
 
-            datafeeds.put(datafeedConfig.getId(), datafeedConfig);
+        public Builder updateDatafeed(DatafeedUpdate update, PersistentTasksInProgress persistentTasksInProgress) {
+            String datafeedId = update.getId();
+            DatafeedConfig oldDatafeedConfig = datafeeds.get(datafeedId);
+            if (oldDatafeedConfig == null) {
+                throw ExceptionsHelper.missingDatafeedException(datafeedId);
+            }
+            checkDatafeedIsStopped(() -> Messages.getMessage(Messages.DATAFEED_CANNOT_UPDATE_IN_CURRENT_STATE, datafeedId,
+                    DatafeedState.STARTED), datafeedId, persistentTasksInProgress);
+            DatafeedConfig newDatafeedConfig = update.apply(oldDatafeedConfig);
+            if (newDatafeedConfig.getJobId().equals(oldDatafeedConfig.getJobId()) == false) {
+                checkJobIsAvailableForDatafeed(newDatafeedConfig.getJobId());
+            }
+            Job job = jobs.get(newDatafeedConfig.getJobId());
+            DatafeedJobValidator.validate(newDatafeedConfig, job);
+            datafeeds.put(datafeedId, newDatafeedConfig);
             return this;
         }
 
@@ -274,17 +298,8 @@ public class MlMetadata implements MetaData.Custom {
             if (datafeed == null) {
                 throw ExceptionsHelper.missingDatafeedException(datafeedId);
             }
-            if (persistentTasksInProgress != null) {
-                Predicate<PersistentTaskInProgress<?>> predicate = t -> {
-                    StartDatafeedAction.Request storedRequest = (StartDatafeedAction.Request) t.getRequest();
-                    return storedRequest.getDatafeedId().equals(datafeedId);
-                };
-                if (persistentTasksInProgress.tasksExist(StartDatafeedAction.NAME, predicate)) {
-                    String msg = Messages.getMessage(Messages.DATAFEED_CANNOT_DELETE_IN_CURRENT_STATE, datafeedId,
-                            DatafeedState.STARTED);
-                    throw ExceptionsHelper.conflictStatusException(msg);
-                }
-            }
+            checkDatafeedIsStopped(() -> Messages.getMessage(Messages.DATAFEED_CANNOT_DELETE_IN_CURRENT_STATE, datafeedId,
+                    DatafeedState.STARTED), datafeedId, persistentTasksInProgress);
             datafeeds.remove(datafeedId);
             return this;
         }
@@ -293,6 +308,18 @@ public class MlMetadata implements MetaData.Custom {
             return datafeeds.values().stream().filter(s -> s.getJobId().equals(jobId)).findFirst();
         }
 
+        private void checkDatafeedIsStopped(Supplier<String> msg, String datafeedId, PersistentTasksInProgress persistentTasksInProgress) {
+            if (persistentTasksInProgress != null) {
+                Predicate<PersistentTaskInProgress<?>> predicate = t -> {
+                    StartDatafeedAction.Request storedRequest = (StartDatafeedAction.Request) t.getRequest();
+                    return storedRequest.getDatafeedId().equals(datafeedId);
+                };
+                if (persistentTasksInProgress.tasksExist(StartDatafeedAction.NAME, predicate)) {
+                    throw ExceptionsHelper.conflictStatusException(msg.get());
+                }
+            }
+        }
+
         private Builder putJobs(Collection<Job> jobs) {
             for (Job job : jobs) {
                 putJob(job, true);

elasticsearch/src/main/java/org/elasticsearch/xpack/ml/rest/datafeeds/RestUpdateDatafeedAction.java

@@ -0,0 +1,37 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License;
+ * you may not use this file except in compliance with the Elastic License.
+ */
+package org.elasticsearch.xpack.ml.rest.datafeeds;
+
+import org.elasticsearch.client.node.NodeClient;
+import org.elasticsearch.common.settings.Settings;
+import org.elasticsearch.common.xcontent.XContentParser;
+import org.elasticsearch.rest.BaseRestHandler;
+import org.elasticsearch.rest.RestController;
+import org.elasticsearch.rest.RestRequest;
+import org.elasticsearch.rest.action.RestToXContentListener;
+import org.elasticsearch.xpack.ml.MlPlugin;
+import org.elasticsearch.xpack.ml.action.UpdateDatafeedAction;
+import org.elasticsearch.xpack.ml.datafeed.DatafeedConfig;
+
+import java.io.IOException;
+
+public class RestUpdateDatafeedAction extends BaseRestHandler {
+
+    public RestUpdateDatafeedAction(Settings settings, RestController controller) {
+        super(settings);
+        controller.registerHandler(RestRequest.Method.POST, MlPlugin.BASE_PATH + "datafeeds/{"
+                + DatafeedConfig.ID.getPreferredName() + "}/_update", this);
+    }
+
+    @Override
+    protected RestChannelConsumer prepareRequest(RestRequest restRequest, NodeClient client) throws IOException {
+        String datafeedId = restRequest.param(DatafeedConfig.ID.getPreferredName());
+        XContentParser parser = restRequest.contentParser();
+        UpdateDatafeedAction.Request updateDatafeedRequest = UpdateDatafeedAction.Request.parseRequest(datafeedId, parser);
+        return channel -> client.execute(UpdateDatafeedAction.INSTANCE, updateDatafeedRequest, new RestToXContentListener<>(channel));
+    }
+
+}

elasticsearch/src/test/java/org/elasticsearch/xpack/ml/action/UpdateDatafeedActionRequestTests.java

@@ -0,0 +1,39 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License;
+ * you may not use this file except in compliance with the Elastic License.
+ */
+package org.elasticsearch.xpack.ml.action;
+
+import org.elasticsearch.common.xcontent.XContentParser;
+import org.elasticsearch.xpack.ml.action.UpdateDatafeedAction.Request;
+import org.elasticsearch.xpack.ml.datafeed.DatafeedConfigTests;
+import org.elasticsearch.xpack.ml.datafeed.DatafeedUpdateTests;
+import org.elasticsearch.xpack.ml.support.AbstractStreamableXContentTestCase;
+import org.junit.Before;
+
+public class UpdateDatafeedActionRequestTests extends AbstractStreamableXContentTestCase<Request> {
+
+    private String datafeedId;
+
+    @Before
+    public void setUpDatafeedId() {
+        datafeedId = DatafeedConfigTests.randomValidDatafeedId();
+    }
+
+    @Override
+    protected Request createTestInstance() {
+        return new Request(DatafeedUpdateTests.createRandomized(datafeedId));
+    }
+
+    @Override
+    protected Request createBlankInstance() {
+        return new Request();
+    }
+
+    @Override
+    protected Request parseInstance(XContentParser parser) {
+        return Request.parseRequest(datafeedId, parser);
+    }
+
+}

elasticsearch/src/test/java/org/elasticsearch/xpack/ml/datafeed/DatafeedConfigTests.java

@@ -25,6 +25,7 @@ import java.util.List;
 
 import static org.hamcrest.Matchers.containsString;
 import static org.hamcrest.Matchers.equalTo;
+import static org.hamcrest.Matchers.is;
 
 public class DatafeedConfigTests extends AbstractSerializingTestCase<DatafeedConfig> {
 
@@ -40,13 +41,17 @@ public class DatafeedConfigTests extends AbstractSerializingTestCase<DatafeedCon
         if (randomBoolean()) {
             builder.setQuery(QueryBuilders.termQuery(randomAsciiOfLength(10), randomAsciiOfLength(10)));
         }
+        boolean addScriptFields = randomBoolean();
+        if (addScriptFields) {
             int scriptsSize = randomInt(3);
             List<SearchSourceBuilder.ScriptField> scriptFields = new ArrayList<>(scriptsSize);
             for (int scriptIndex = 0; scriptIndex < scriptsSize; scriptIndex++) {
                 scriptFields.add(new SearchSourceBuilder.ScriptField(randomAsciiOfLength(10), new Script(randomAsciiOfLength(10)),
                         randomBoolean()));
             }
-        if (randomBoolean() && scriptsSize == 0) {
+            builder.setScriptFields(scriptFields);
+        }
+        if (randomBoolean() && addScriptFields == false) {
             // can only test with a single agg as the xcontent order gets randomized by test base class and then
             // the actual xcontent isn't the same and test fail.
             // Testing with a single agg is ok as we don't have special list writeable / xconent logic
@@ -54,7 +59,6 @@ public class DatafeedConfigTests extends AbstractSerializingTestCase<DatafeedCon
             aggs.addAggregator(AggregationBuilders.avg(randomAsciiOfLength(10)).field(randomAsciiOfLength(10)));
             builder.setAggregations(aggs);
         }
-        builder.setScriptFields(scriptFields);
         if (randomBoolean()) {
             builder.setScrollSize(randomIntBetween(0, Integer.MAX_VALUE));
         }
@@ -73,7 +77,7 @@ public class DatafeedConfigTests extends AbstractSerializingTestCase<DatafeedCon
         return builder.build();
     }
 
-    private static List<String> randomStringList(int min, int max) {
+    public static List<String> randomStringList(int min, int max) {
         int size = scaledRandomIntBetween(min, max);
         List<String> list = new ArrayList<>();
         for (int i = 0; i < size; i++) {
@@ -257,6 +261,35 @@ public class DatafeedConfigTests extends AbstractSerializingTestCase<DatafeedCon
         assertThat(e.getMessage(), equalTo("script_fields cannot be used in combination with aggregations"));
     }
 
+    public void testHasAggregations_GivenNull() {
+        DatafeedConfig.Builder builder = new DatafeedConfig.Builder("datafeed1", "job1");
+        builder.setIndexes(Arrays.asList("myIndex"));
+        builder.setTypes(Arrays.asList("myType"));
+        DatafeedConfig datafeedConfig = builder.build();
+
+        assertThat(datafeedConfig.hasAggregations(), is(false));
+    }
+
+    public void testHasAggregations_GivenEmpty() {
+        DatafeedConfig.Builder builder = new DatafeedConfig.Builder("datafeed1", "job1");
+        builder.setIndexes(Arrays.asList("myIndex"));
+        builder.setTypes(Arrays.asList("myType"));
+        builder.setAggregations(new AggregatorFactories.Builder());
+        DatafeedConfig datafeedConfig = builder.build();
+
+        assertThat(datafeedConfig.hasAggregations(), is(false));
+    }
+
+    public void testHasAggregations_NonEmpty() {
+        DatafeedConfig.Builder builder = new DatafeedConfig.Builder("datafeed1", "job1");
+        builder.setIndexes(Arrays.asList("myIndex"));
+        builder.setTypes(Arrays.asList("myType"));
+        builder.setAggregations(new AggregatorFactories.Builder().addAggregator(AggregationBuilders.avg("foo")));
+        DatafeedConfig datafeedConfig = builder.build();
+
+        assertThat(datafeedConfig.hasAggregations(), is(true));
+    }
+
     public void testDomainSplitInjection() {
         DatafeedConfig.Builder datafeed = new DatafeedConfig.Builder("datafeed1", "job1");
         datafeed.setIndexes(Arrays.asList("my_index"));

elasticsearch/src/test/java/org/elasticsearch/xpack/ml/datafeed/DatafeedJobRunnerTests.java

@@ -14,6 +14,7 @@ import org.elasticsearch.cluster.metadata.MetaData;
 import org.elasticsearch.cluster.service.ClusterService;
 import org.elasticsearch.common.unit.TimeValue;
 import org.elasticsearch.mock.orig.Mockito;
+import org.elasticsearch.search.aggregations.AggregationBuilders;
 import org.elasticsearch.search.aggregations.AggregatorFactories;
 import org.elasticsearch.test.ESTestCase;
 import org.elasticsearch.threadpool.ThreadPool;
@@ -254,13 +255,13 @@ public class DatafeedJobRunnerTests extends ESTestCase {
         assertThat(dataExtractorFactory, instanceOf(ScrollDataExtractorFactory.class));
     }
 
-    public void testCreateDataExtractorFactoryGivenDefaultAggregation() {
+    public void testCreateDataExtractorFactoryGivenAggregation() {
         DataDescription.Builder dataDescription = new DataDescription.Builder();
         dataDescription.setTimeField("time");
         Job.Builder jobBuilder = createDatafeedJob();
         jobBuilder.setDataDescription(dataDescription);
         DatafeedConfig.Builder datafeedConfig = createDatafeedConfig("datafeed1", "foo");
-        datafeedConfig.setAggregations(AggregatorFactories.builder());
+        datafeedConfig.setAggregations(AggregatorFactories.builder().addAggregator(AggregationBuilders.avg("a")));
         DatafeedJobRunner runner = new DatafeedJobRunner(threadPool, client, clusterService, mock(JobProvider.class), () -> currentTime);
 
         DataExtractorFactory dataExtractorFactory = runner.createDataExtractorFactory(datafeedConfig.build(), jobBuilder.build());

elasticsearch/src/test/java/org/elasticsearch/xpack/ml/datafeed/DatafeedUpdateTests.java

@@ -0,0 +1,165 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License;
+ * you may not use this file except in compliance with the Elastic License.
+ */
+package org.elasticsearch.xpack.ml.datafeed;
+
+import org.elasticsearch.common.io.stream.Writeable;
+import org.elasticsearch.common.xcontent.XContentParser;
+import org.elasticsearch.index.query.QueryBuilders;
+import org.elasticsearch.script.Script;
+import org.elasticsearch.search.aggregations.AggregationBuilders;
+import org.elasticsearch.search.aggregations.AggregatorFactories;
+import org.elasticsearch.search.builder.SearchSourceBuilder;
+import org.elasticsearch.xpack.ml.support.AbstractSerializingTestCase;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+import static org.hamcrest.Matchers.equalTo;
+import static org.hamcrest.Matchers.is;
+
+public class DatafeedUpdateTests extends AbstractSerializingTestCase<DatafeedUpdate> {
+
+    @Override
+    protected DatafeedUpdate createTestInstance() {
+        return createRandomized(DatafeedConfigTests.randomValidDatafeedId());
+    }
+
+    public static DatafeedUpdate createRandomized(String datafeedId) {
+        DatafeedUpdate.Builder builder = new DatafeedUpdate.Builder(datafeedId);
+        if (randomBoolean()) {
+            builder.setJobId(randomAsciiOfLength(10));
+        }
+        if (randomBoolean()) {
+            builder.setQueryDelay(randomNonNegativeLong());
+        }
+        if (randomBoolean()) {
+            builder.setFrequency(randomNonNegativeLong());
+        }
+        if (randomBoolean()) {
+            builder.setIndexes(DatafeedConfigTests.randomStringList(1, 10));
+        }
+        if (randomBoolean()) {
+            builder.setTypes(DatafeedConfigTests.randomStringList(1, 10));
+        }
+        if (randomBoolean()) {
+            builder.setQuery(QueryBuilders.termQuery(randomAsciiOfLength(10), randomAsciiOfLength(10)));
+        }
+        if (randomBoolean()) {
+            int scriptsSize = randomInt(3);
+            List<SearchSourceBuilder.ScriptField> scriptFields = new ArrayList<>(scriptsSize);
+            for (int scriptIndex = 0; scriptIndex < scriptsSize; scriptIndex++) {
+                scriptFields.add(new SearchSourceBuilder.ScriptField(randomAsciiOfLength(10), new Script(randomAsciiOfLength(10)),
+                        randomBoolean()));
+            }
+            builder.setScriptFields(scriptFields);
+        }
+        if (randomBoolean()) {
+            // can only test with a single agg as the xcontent order gets randomized by test base class and then
+            // the actual xcontent isn't the same and test fail.
+            // Testing with a single agg is ok as we don't have special list writeable / xconent logic
+            AggregatorFactories.Builder aggs = new AggregatorFactories.Builder();
+            aggs.addAggregator(AggregationBuilders.avg(randomAsciiOfLength(10)).field(randomAsciiOfLength(10)));
+            builder.setAggregations(aggs);
+        }
+        if (randomBoolean()) {
+            builder.setScrollSize(randomIntBetween(0, Integer.MAX_VALUE));
+        }
+        if (randomBoolean()) {
+            builder.setSource(randomBoolean());
+        }
+        if (randomBoolean()) {
+            builder.setChunkingConfig(ChunkingConfigTests.createRandomizedChunk());
+        }
+        return builder.build();
+    }
+
+    @Override
+    protected Writeable.Reader<DatafeedUpdate> instanceReader() {
+        return DatafeedUpdate::new;
+    }
+
+    @Override
+    protected DatafeedUpdate parseInstance(XContentParser parser) {
+        return DatafeedUpdate.PARSER.apply(parser, null).build();
+    }
+
+    public void testApply_failBecauseTargetDatafeedHasDifferentId() {
+        DatafeedConfig datafeed = DatafeedConfigTests.createRandomizedDatafeedConfig("foo");
+        expectThrows(IllegalArgumentException.class, () -> createRandomized(datafeed.getId() + "_2").apply(datafeed));
+    }
+
+    public void testApply_givenEmptyUpdate() {
+        DatafeedConfig datafeed = DatafeedConfigTests.createRandomizedDatafeedConfig("foo");
+        DatafeedConfig updatedDatafeed = new DatafeedUpdate.Builder(datafeed.getId()).build().apply(datafeed);
+        assertThat(datafeed, equalTo(updatedDatafeed));
+    }
+
+    public void testApply_givenPartialUpdate() {
+        DatafeedConfig datafeed = DatafeedConfigTests.createRandomizedDatafeedConfig("foo");
+        DatafeedUpdate.Builder update = new DatafeedUpdate.Builder(datafeed.getId());
+        update.setScrollSize(datafeed.getScrollSize() + 1);
+
+        DatafeedUpdate.Builder updated = new DatafeedUpdate.Builder(datafeed.getId());
+        updated.setScrollSize(datafeed.getScrollSize() + 1);
+        DatafeedConfig updatedDatafeed = update.build().apply(datafeed);
+
+        DatafeedConfig.Builder expectedDatafeed = new DatafeedConfig.Builder(datafeed);
+        expectedDatafeed.setScrollSize(datafeed.getScrollSize() + 1);
+        assertThat(updatedDatafeed, equalTo(expectedDatafeed.build()));
+    }
+
+    public void testApply_givenFullUpdateNoAggregations() {
+        DatafeedConfig.Builder datafeedBuilder = new DatafeedConfig.Builder("foo", "foo-feed");
+        datafeedBuilder.setIndexes(Arrays.asList("i_1"));
+        datafeedBuilder.setTypes(Arrays.asList("t_1"));
+        DatafeedConfig datafeed = datafeedBuilder.build();
+
+        DatafeedUpdate.Builder update = new DatafeedUpdate.Builder(datafeed.getId());
+        update.setJobId("bar");
+        update.setIndexes(Arrays.asList("i_2"));
+        update.setTypes(Arrays.asList("t_2"));
+        update.setQueryDelay(42L);
+        update.setFrequency(142L);
+        update.setQuery(QueryBuilders.termQuery("a", "b"));
+        update.setScriptFields(Arrays.asList(new SearchSourceBuilder.ScriptField("a", new Script("b"), false)));
+        update.setScrollSize(8000);
+        update.setSource(true);
+        update.setChunkingConfig(ChunkingConfig.newManual(3600L));
+
+        DatafeedConfig updatedDatafeed = update.build().apply(datafeed);
+
+        assertThat(updatedDatafeed.getJobId(), equalTo("bar"));
+        assertThat(updatedDatafeed.getIndexes(), equalTo(Arrays.asList("i_2")));
+        assertThat(updatedDatafeed.getTypes(), equalTo(Arrays.asList("t_2")));
+        assertThat(updatedDatafeed.getQueryDelay(), equalTo(42L));
+        assertThat(updatedDatafeed.getFrequency(), equalTo(142L));
+        assertThat(updatedDatafeed.getQuery(), equalTo(QueryBuilders.termQuery("a", "b")));
+        assertThat(updatedDatafeed.hasAggregations(), is(false));
+        assertThat(updatedDatafeed.getScriptFields(),
+                equalTo(Arrays.asList(new SearchSourceBuilder.ScriptField("a", new Script("b"), false))));
+        assertThat(updatedDatafeed.getScrollSize(), equalTo(8000));
+        assertThat(updatedDatafeed.isSource(), is(true));
+        assertThat(updatedDatafeed.getChunkingConfig(), equalTo(ChunkingConfig.newManual(3600L)));
+    }
+
+    public void testApply_givenAggregations() {
+        DatafeedConfig.Builder datafeedBuilder = new DatafeedConfig.Builder("foo", "foo-feed");
+        datafeedBuilder.setIndexes(Arrays.asList("i_1"));
+        datafeedBuilder.setTypes(Arrays.asList("t_1"));
+        DatafeedConfig datafeed = datafeedBuilder.build();
+
+        DatafeedUpdate.Builder update = new DatafeedUpdate.Builder(datafeed.getId());
+        update.setAggregations(new AggregatorFactories.Builder().addAggregator(AggregationBuilders.avg("a")));
+
+        DatafeedConfig updatedDatafeed = update.build().apply(datafeed);
+
+        assertThat(updatedDatafeed.getIndexes(), equalTo(Arrays.asList("i_1")));
+        assertThat(updatedDatafeed.getTypes(), equalTo(Arrays.asList("t_1")));
+        assertThat(updatedDatafeed.getAggregations(),
+                equalTo(new AggregatorFactories.Builder().addAggregator(AggregationBuilders.avg("a"))));
+    }
+}

elasticsearch/src/test/java/org/elasticsearch/xpack/ml/job/metadata/MlMetadataTests.java

@@ -19,6 +19,7 @@ import org.elasticsearch.xpack.ml.action.OpenJobAction;
 import org.elasticsearch.xpack.ml.action.StartDatafeedAction;
 import org.elasticsearch.xpack.ml.datafeed.DatafeedConfig;
 import org.elasticsearch.xpack.ml.datafeed.DatafeedConfigTests;
+import org.elasticsearch.xpack.ml.datafeed.DatafeedUpdate;
 import org.elasticsearch.xpack.ml.job.config.AnalysisConfig;
 import org.elasticsearch.xpack.ml.job.config.Job;
 import org.elasticsearch.xpack.ml.job.config.JobState;
@@ -47,7 +48,7 @@ public class MlMetadataTests extends AbstractSerializingTestCase<MlMetadata> {
             Job job = JobTests.createRandomizedJob();
             if (randomBoolean()) {
                 DatafeedConfig datafeedConfig = DatafeedConfigTests.createRandomizedDatafeedConfig(job.getId());
-                if (datafeedConfig.getAggregations() != null) {
+                if (datafeedConfig.hasAggregations()) {
                     AnalysisConfig.Builder analysisConfig = new AnalysisConfig.Builder(job.getAnalysisConfig().getDetectors());
                     analysisConfig.setSummaryCountFieldName("doc_count");
                     Job.Builder jobBuilder = new Job.Builder(job);
@@ -236,6 +237,90 @@ public class MlMetadataTests extends AbstractSerializingTestCase<MlMetadata> {
         expectThrows(IllegalArgumentException.class, () -> builder.putDatafeed(datafeedConfig1));
     }
 
+    public void testUpdateDatafeed() {
+        Job job1 = createDatafeedJob().build();
+        DatafeedConfig datafeedConfig1 = createDatafeedConfig("datafeed1", job1.getId()).build();
+        MlMetadata.Builder builder = new MlMetadata.Builder();
+        builder.putJob(job1, false);
+        builder.putDatafeed(datafeedConfig1);
+        MlMetadata beforeMetadata = builder.build();
+
+        DatafeedUpdate.Builder update = new DatafeedUpdate.Builder(datafeedConfig1.getId());
+        update.setScrollSize(5000);
+        MlMetadata updatedMetadata = new MlMetadata.Builder(beforeMetadata).updateDatafeed(update.build(), null).build();
+
+        DatafeedConfig updatedDatafeed = updatedMetadata.getDatafeed(datafeedConfig1.getId());
+        assertThat(updatedDatafeed.getJobId(), equalTo(datafeedConfig1.getJobId()));
+        assertThat(updatedDatafeed.getIndexes(), equalTo(datafeedConfig1.getIndexes()));
+        assertThat(updatedDatafeed.getTypes(), equalTo(datafeedConfig1.getTypes()));
+        assertThat(updatedDatafeed.getScrollSize(), equalTo(5000));
+    }
+
+    public void testUpdateDatafeed_failBecauseDatafeedDoesNotExist() {
+        DatafeedUpdate.Builder update = new DatafeedUpdate.Builder("foo");
+        update.setScrollSize(5000);
+        expectThrows(ResourceNotFoundException.class, () -> new MlMetadata.Builder().updateDatafeed(update.build(), null).build());
+    }
+
+    public void testUpdateDatafeed_failBecauseDatafeedIsNotStopped() {
+        Job job1 = createDatafeedJob().build();
+        DatafeedConfig datafeedConfig1 = createDatafeedConfig("datafeed1", job1.getId()).build();
+        MlMetadata.Builder builder = new MlMetadata.Builder();
+        builder.putJob(job1, false);
+        builder.putDatafeed(datafeedConfig1);
+        MlMetadata beforeMetadata = builder.build();
+
+        StartDatafeedAction.Request request = new StartDatafeedAction.Request(datafeedConfig1.getId(), 0L);
+        PersistentTaskInProgress<StartDatafeedAction.Request> taskInProgress =
+                new PersistentTaskInProgress<>(0, StartDatafeedAction.NAME, request, null);
+        PersistentTasksInProgress tasksInProgress =
+                new PersistentTasksInProgress(1, Collections.singletonMap(taskInProgress.getId(), taskInProgress));
+
+        DatafeedUpdate.Builder update = new DatafeedUpdate.Builder(datafeedConfig1.getId());
+        update.setScrollSize(5000);
+
+        ElasticsearchStatusException e = expectThrows(ElasticsearchStatusException.class,
+                () -> new MlMetadata.Builder(beforeMetadata).updateDatafeed(update.build(), tasksInProgress));
+        assertThat(e.status(), equalTo(RestStatus.CONFLICT));
+    }
+
+    public void testUpdateDatafeed_failBecauseNewJobIdDoesNotExist() {
+        Job job1 = createDatafeedJob().build();
+        DatafeedConfig datafeedConfig1 = createDatafeedConfig("datafeed1", job1.getId()).build();
+        MlMetadata.Builder builder = new MlMetadata.Builder();
+        builder.putJob(job1, false);
+        builder.putDatafeed(datafeedConfig1);
+        MlMetadata beforeMetadata = builder.build();
+
+        DatafeedUpdate.Builder update = new DatafeedUpdate.Builder(datafeedConfig1.getId());
+        update.setJobId(job1.getId() + "_2");
+
+        expectThrows(ResourceNotFoundException.class,
+                () -> new MlMetadata.Builder(beforeMetadata).updateDatafeed(update.build(), null));
+    }
+
+    public void testUpdateDatafeed_failBecauseNewJobHasAnotherDatafeedAttached() {
+        Job job1 = createDatafeedJob().build();
+        Job.Builder job2 = new Job.Builder(job1);
+        job2.setId(job1.getId() + "_2");
+        DatafeedConfig datafeedConfig1 = createDatafeedConfig("datafeed1", job1.getId()).build();
+        DatafeedConfig datafeedConfig2 = createDatafeedConfig("datafeed2", job2.getId()).build();
+        MlMetadata.Builder builder = new MlMetadata.Builder();
+        builder.putJob(job1, false);
+        builder.putJob(job2.build(), false);
+        builder.putDatafeed(datafeedConfig1);
+        builder.putDatafeed(datafeedConfig2);
+        MlMetadata beforeMetadata = builder.build();
+
+        DatafeedUpdate.Builder update = new DatafeedUpdate.Builder(datafeedConfig1.getId());
+        update.setJobId(job2.getId());
+
+        ElasticsearchStatusException e = expectThrows(ElasticsearchStatusException.class,
+                () -> new MlMetadata.Builder(beforeMetadata).updateDatafeed(update.build(), null));
+        assertThat(e.status(), equalTo(RestStatus.CONFLICT));
+        assertThat(e.getMessage(), equalTo("A datafeed [datafeed2] already exists for job [foo_2]"));
+    }
+
     public void testRemoveDatafeed_failBecauseDatafeedStarted() {
         Job job1 = createDatafeedJob().build();
         DatafeedConfig datafeedConfig1 = createDatafeedConfig("datafeed1", job1.getId()).build();

elasticsearch/src/test/resources/org/elasticsearch/transport/actions

@@ -113,6 +113,7 @@ cluster:admin/ml/anomaly_detectors/model_snapshots/get
 cluster:admin/ml/anomaly_detectors/results/records/get
 cluster:admin/ml/anomaly_detectors/results/influencers/get
 cluster:admin/ml/datafeeds/put
+cluster:admin/ml/datafeeds/update
 cluster:admin/ml/anomaly_detectors/model_snapshots/delete
 cluster:admin/ml/anomaly_detectors/validate/detector
 cluster:admin/ml/anomaly_detectors/validate

elasticsearch/src/test/resources/rest-api-spec/api/xpack.ml.update_datafeed.json

@@ -0,0 +1,20 @@
+{
+  "xpack.ml.update_datafeed": {
+    "methods": [ "POST" ],
+    "url": {
+      "path": "/_xpack/ml/datafeeds/{datafeed_id}/_update",
+      "paths": [ "/_xpack/ml/datafeeds/{datafeed_id}/_update" ],
+      "parts": {
+        "datafeed_id": {
+          "type": "string",
+          "required": true,
+          "description": "The ID of the datafeed to update"
+        }
+      }
+    },
+    "body": {
+      "description" : "The datafeed update settings",
+      "required" : true
+    }
+  }
+}

elasticsearch/src/test/resources/rest-api-spec/test/ml/datafeeds_crud.yaml

@@ -133,6 +133,121 @@ setup:
             "query":{"match_all_mispelled":{}}
           }
 
+---
+"Test update datafeed":
+  - do:
+      xpack.ml.put_datafeed:
+        datafeed_id: test-datafeed-1
+        body:  >
+          {
+            "job_id":"job-1",
+            "indexes":["index-foo"],
+            "types":["type-bar"],
+            "scroll_size": 2000
+          }
+
+  - do:
+      xpack.ml.update_datafeed:
+        datafeed_id: test-datafeed-1
+        body:  >
+          {
+            "indexes":["index-*"],
+            "scroll_size": 10000
+          }
+  - match: { datafeed_id: "test-datafeed-1" }
+  - match: { job_id: "job-1" }
+  - match: { indexes: ["index-*"] }
+  - match: { types: ["type-bar"] }
+  - match: { scroll_size: 10000 }
+
+---
+"Test update datafeed to point to different job":
+  - do:
+      xpack.ml.put_datafeed:
+        datafeed_id: test-datafeed-1
+        body:  >
+          {
+            "job_id":"job-1",
+            "indexes":["index-foo"],
+            "types":["type-bar"],
+            "scroll_size": 2000
+          }
+
+  - do:
+      xpack.ml.update_datafeed:
+        datafeed_id: test-datafeed-1
+        body:  >
+          {
+            "job_id": "job-2"
+          }
+  - match: { datafeed_id: "test-datafeed-1" }
+  - match: { job_id: "job-2" }
+  - match: { indexes: ["index-foo"] }
+  - match: { types: ["type-bar"] }
+
+---
+"Test update datafeed with missing id":
+
+  - do:
+      catch: /resource_not_found_exception/
+      xpack.ml.update_datafeed:
+        datafeed_id: a-missing-datafeed
+        body:  >
+          {}
+
+---
+"Test update datafeed to point to missing job":
+  - do:
+      xpack.ml.put_datafeed:
+        datafeed_id: test-datafeed-1
+        body:  >
+          {
+            "job_id":"job-1",
+            "indexes":["index-foo"],
+            "types":["type-bar"],
+            "scroll_size": 2000
+          }
+
+  - do:
+      catch: /resource_not_found_exception/
+      xpack.ml.update_datafeed:
+        datafeed_id: test-datafeed-1
+        body:  >
+          {
+            "job_id": "job-3"
+          }
+
+---
+"Test update datafeed to point to job already attached to another datafeed":
+  - do:
+      xpack.ml.put_datafeed:
+        datafeed_id: test-datafeed-1
+        body:  >
+          {
+            "job_id":"job-1",
+            "indexes":["index-foo"],
+            "types":["type-bar"]
+          }
+
+  - do:
+      xpack.ml.put_datafeed:
+        datafeed_id: test-datafeed-2
+        body:  >
+          {
+            "job_id":"job-2",
+            "indexes":["index-foo"],
+            "types":["type-bar"]
+          }
+
+  - do:
+      catch: /A datafeed \[test-datafeed-2\] already exists for job \[job-2\]/
+      xpack.ml.update_datafeed:
+        datafeed_id: test-datafeed-1
+        body:  >
+          {
+            "job_id": "job-2"
+          }
+
 ---
 "Test delete datafeed with missing id":
   - do: