Ensure all Steps have Javadoc (#35757)

Adds or corrects Javadoc on subclasses of Step.

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/indexlifecycle/AllocationRoutedStep.java

@@ -32,6 +32,9 @@ import java.io.IOException;
 import java.util.Collections;
 import java.util.Objects;
 
+/**
+ * Checks whether all shards have been correctly routed in response to an update to the allocation rules for an index.
+ */
 public class AllocationRoutedStep extends ClusterStateWaitStep {
     public static final String NAME = "check-allocation";
 

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/indexlifecycle/AsyncActionStep.java

@@ -9,6 +9,9 @@ import org.elasticsearch.client.Client;
 import org.elasticsearch.cluster.ClusterState;
 import org.elasticsearch.cluster.metadata.IndexMetaData;
 
+/**
+ * Performs an action which must be performed asynchronously because it may take time to complete.
+ */
 public abstract class AsyncActionStep extends Step {
 
     private Client client;

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/indexlifecycle/AsyncWaitStep.java

@@ -9,6 +9,12 @@ import org.elasticsearch.client.Client;
 import org.elasticsearch.cluster.metadata.IndexMetaData;
 import org.elasticsearch.common.xcontent.ToXContentObject;
 
+/**
+ * A step which will be called periodically, waiting for some condition to become true.
+ * Called asynchronously, as the condition may take time to check.
+ *
+ * If checking something based on the current cluster state which does not take time to check, use {@link ClusterStateWaitStep}.
+ */
 public abstract class AsyncWaitStep extends Step {
 
     private Client client;

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/indexlifecycle/ClusterStateActionStep.java

@@ -8,6 +8,9 @@ package org.elasticsearch.xpack.core.indexlifecycle;
 import org.elasticsearch.cluster.ClusterState;
 import org.elasticsearch.index.Index;
 
+/**
+ * Updates the cluster state, similar to {@link org.elasticsearch.cluster.ClusterStateUpdateTask}.
+ */
 public abstract class ClusterStateActionStep extends Step {
 
     public ClusterStateActionStep(StepKey key, StepKey nextStepKey) {

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/indexlifecycle/ClusterStateWaitStep.java

@@ -9,6 +9,11 @@ import org.elasticsearch.cluster.ClusterState;
 import org.elasticsearch.common.xcontent.ToXContentObject;
 import org.elasticsearch.index.Index;
 
+/**
+ * Checks whether a condition has been met based on the cluster state.
+ *
+ * If checking a condition not based on the cluster state, or which may take time to evaluate, use {@link AsyncWaitStep}.
+ */
 public abstract class ClusterStateWaitStep extends Step {
 
     public ClusterStateWaitStep(StepKey key, StepKey nextStepKey) {

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/indexlifecycle/DeleteStep.java

@@ -11,6 +11,9 @@ import org.elasticsearch.client.Client;
 import org.elasticsearch.cluster.ClusterState;
 import org.elasticsearch.cluster.metadata.IndexMetaData;
 
+/**
+ * Deletes a single index.
+ */
 public class DeleteStep extends AsyncActionStep {
     public static final String NAME = "delete";
 

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/indexlifecycle/ErrorStep.java

@@ -5,6 +5,9 @@
  */
 package org.elasticsearch.xpack.core.indexlifecycle;
 
+/**
+ * Signals that an error was encountered during the execution of a policy on an index.
+ */
 public class ErrorStep extends Step {
     public static final String NAME = "ERROR";
 

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/indexlifecycle/ForceMergeStep.java

@@ -13,6 +13,9 @@ import org.elasticsearch.cluster.metadata.IndexMetaData;
 
 import java.util.Objects;
 
+/**
+ * Invokes a force merge on a single index.
+ */
 public class ForceMergeStep extends AsyncActionStep {
     public static final String NAME = "forcemerge";
     private final int maxNumSegments;

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/indexlifecycle/InitializePolicyContextStep.java

@@ -14,6 +14,9 @@ import org.elasticsearch.index.Index;
 
 import static org.elasticsearch.xpack.core.indexlifecycle.LifecycleExecutionState.ILM_CUSTOM_METADATA_KEY;
 
+/**
+ * Initializes the {@link LifecycleExecutionState} for an index. This should be the first Step called on an index.
+ */
 public final class InitializePolicyContextStep extends ClusterStateActionStep {
     public static final String INITIALIZATION_PHASE = "new";
     public static final StepKey KEY = new StepKey(INITIALIZATION_PHASE, "init", "init");

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/indexlifecycle/SegmentCountStep.java

@@ -21,7 +21,7 @@ import java.util.Objects;
 import java.util.stream.StreamSupport;
 
 /**
- * This {@link Step} evaluates whether force_merge was successful
+ * This {@link Step} evaluates whether force_merge was successful by checking the segment count.
  */
 public class SegmentCountStep extends AsyncWaitStep {
     public static final String NAME = "segment-count";

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/indexlifecycle/SetSingleNodeAllocateStep.java

@@ -27,6 +27,10 @@ import java.util.Collections;
 import java.util.List;
 import java.util.Optional;
 
+/**
+ * Allocates all shards in a single index to one node.
+ * For example, as preparation for shrinking that index.
+ */
 public class SetSingleNodeAllocateStep extends AsyncActionStep {
     public static final String NAME = "set-single-node-allocation";
 

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/indexlifecycle/ShrinkSetAliasStep.java

@@ -13,6 +13,10 @@ import org.elasticsearch.cluster.metadata.IndexMetaData;
 
 import java.util.Objects;
 
+/**
+ * Following shrinking an index and deleting the original index, this step creates an alias with the same name as the original index which
+ * points to the new shrunken index to allow clients to continue to use the original index name without being aware that it has shrunk.
+ */
 public class ShrinkSetAliasStep extends AsyncActionStep {
     public static final String NAME = "aliases";
     private String shrunkIndexPrefix;

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/indexlifecycle/ShrinkStep.java

@@ -15,6 +15,9 @@ import org.elasticsearch.common.settings.Settings;
 
 import java.util.Objects;
 
+/**
+ * Shrinks an index, using a prefix prepended to the original index name for the name of the shrunken index.
+ */
 public class ShrinkStep extends AsyncActionStep {
     public static final String NAME = "shrink";
 

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/indexlifecycle/ShrunkShardsAllocatedStep.java

@@ -17,6 +17,9 @@ import org.elasticsearch.index.Index;
 import java.io.IOException;
 import java.util.Objects;
 
+/**
+ * Checks whether all shards in a shrunken index have been successfully allocated.
+ */
 public class ShrunkShardsAllocatedStep extends ClusterStateWaitStep {
     public static final String NAME = "shrunk-shards-allocated";
     private String shrunkIndexPrefix;

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/indexlifecycle/ShrunkenIndexCheckStep.java

@@ -19,6 +19,10 @@ import org.elasticsearch.index.Index;
 import java.io.IOException;
 import java.util.Objects;
 
+/**
+ * Verifies that an index was created through a shrink operation, rather than created some other way.
+ * Also checks the name of the index to ensure it aligns with what is expected from an index shrunken via a previous step.
+ */
 public class ShrunkenIndexCheckStep extends ClusterStateWaitStep {
     public static final String NAME = "is-shrunken-index";
     private static final Logger logger = LogManager.getLogger(InitializePolicyContextStep.class);

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/indexlifecycle/Step.java

@@ -19,7 +19,7 @@ import java.io.IOException;
 import java.util.Objects;
 
 /**
- * A {@link LifecycleAction} which deletes the index.
+ * Represents one part of the execution of a {@link LifecycleAction}.
  */
 public abstract class Step {
     private final StepKey key;

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/indexlifecycle/TerminalPolicyStep.java

@@ -5,6 +5,9 @@
  */
 package org.elasticsearch.xpack.core.indexlifecycle;
 
+/**
+ * Signals that the policy for an index has been fully executed.
+ */
 public class TerminalPolicyStep extends Step {
     public static final String COMPLETED_PHASE = "completed";
     public static final StepKey KEY = new StepKey(COMPLETED_PHASE, "completed", "completed");

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/indexlifecycle/UpdateRolloverLifecycleDateStep.java

@@ -14,6 +14,10 @@ import org.elasticsearch.index.Index;
 
 import static org.elasticsearch.xpack.core.indexlifecycle.LifecycleExecutionState.ILM_CUSTOM_METADATA_KEY;
 
+/**
+ * Copies the lifecycle reference date to a new index created by rolling over an alias.
+ * Used so that the "age" of an index doesn't get reset on rollover.
+ */
 public class UpdateRolloverLifecycleDateStep extends ClusterStateActionStep {
     public static final String NAME = "update-rollover-lifecycle-date";
 

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/indexlifecycle/UpdateSettingsStep.java

@@ -14,6 +14,9 @@ import org.elasticsearch.common.settings.Settings;
 
 import java.util.Objects;
 
+/**
+ * Updates the settings for an index.
+ */
 public class UpdateSettingsStep extends AsyncActionStep {
     public static final String NAME = "update-settings";