HBASE-20656 Validate pre-2.0 coprocessors against HBase 2.0+

Signed-off-by: Mike Drob <mdrob@apache.org>

hbase-checkstyle/src/main/resources/hbase/checkstyle-suppressions.xml

@@ -38,4 +38,5 @@
   <suppress checks="InterfaceIsTypeCheck" files=".*/src/main/.*\.java"/>
   <suppress checks="EmptyBlockCheck" files="TBoundedThreadPoolServer.java"/>
   <suppress checks="EqualsHashCode" files="StartcodeAgnosticServerName.java"/>
+  <suppress checks="MethodLength" files="Branch1CoprocessorMethods.java"/>
 </suppressions>

hbase-common/src/main/java/org/apache/hadoop/hbase/util/AbstractHBaseTool.java

@@ -22,7 +22,6 @@ import java.util.Comparator;
 import java.util.HashMap;
 import java.util.List;
 
-import org.apache.hadoop.conf.Configurable;
 import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.hbase.HBaseConfiguration;
 import org.apache.hadoop.util.Tool;
@@ -46,9 +45,9 @@ import org.apache.hbase.thirdparty.org.apache.commons.cli.ParseException;
  * command-line argument parsing.
  */
 @InterfaceAudience.Private
-public abstract class AbstractHBaseTool implements Tool, Configurable {
-  protected static final int EXIT_SUCCESS = 0;
-  protected static final int EXIT_FAILURE = 1;
+public abstract class AbstractHBaseTool implements Tool {
+  public static final int EXIT_SUCCESS = 0;
+  public static final int EXIT_FAILURE = 1;
 
   public static final String SHORT_HELP_OPTION = "h";
   public static final String LONG_HELP_OPTION = "help";

hbase-server/src/main/java/org/apache/hadoop/hbase/coprocessor/BulkLoadObserver.java

@@ -21,13 +21,9 @@ package org.apache.hadoop.hbase.coprocessor;
 
 import java.io.IOException;
 
-import org.apache.hadoop.hbase.Coprocessor;
 import org.apache.hadoop.hbase.HBaseInterfaceAudience;
-import org.apache.hadoop.hbase.TableName;
 import org.apache.yetus.audience.InterfaceAudience;
 import org.apache.yetus.audience.InterfaceStability;
-import org.apache.hadoop.hbase.shaded.protobuf.generated.ClientProtos.PrepareBulkLoadRequest;
-import org.apache.hadoop.hbase.shaded.protobuf.generated.ClientProtos.CleanupBulkLoadRequest;
 
 /**
  * Coprocessors implement this interface to observe and mediate bulk load operations.
@@ -55,7 +51,7 @@ public interface BulkLoadObserver {
       * It can't bypass the default action, e.g., ctx.bypass() won't have effect.
       * If you need to get the region or table name, get it from the
       * <code>ctx</code> as follows: <code>code>ctx.getEnvironment().getRegion()</code>. Use
-      * getRegionInfo to fetch the encodedName and use getTabldDescriptor() to get the tableName.
+      * getRegionInfo to fetch the encodedName and use getTableDescriptor() to get the tableName.
       * @param ctx the environment to interact with the framework and master
       */
     default void prePrepareBulkLoad(ObserverContext<RegionCoprocessorEnvironment> ctx)
@@ -66,7 +62,7 @@ public interface BulkLoadObserver {
       * It can't bypass the default action, e.g., ctx.bypass() won't have effect.
       * If you need to get the region or table name, get it from the
       * <code>ctx</code> as follows: <code>code>ctx.getEnvironment().getRegion()</code>. Use
-      * getRegionInfo to fetch the encodedName and use getTabldDescriptor() to get the tableName.
+      * getRegionInfo to fetch the encodedName and use getTableDescriptor() to get the tableName.
       * @param ctx the environment to interact with the framework and master
       */
     default void preCleanupBulkLoad(ObserverContext<RegionCoprocessorEnvironment> ctx)

hbase-server/src/main/java/org/apache/hadoop/hbase/tool/DataBlockEncodingValidator.java

@@ -0,0 +1,108 @@
+/**
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hbase.tool;
+
+import java.io.IOException;
+import java.util.List;
+
+import org.apache.hadoop.hbase.HBaseInterfaceAudience;
+import org.apache.hadoop.hbase.client.Admin;
+import org.apache.hadoop.hbase.client.ColumnFamilyDescriptor;
+import org.apache.hadoop.hbase.client.Connection;
+import org.apache.hadoop.hbase.client.ConnectionFactory;
+import org.apache.hadoop.hbase.client.TableDescriptor;
+import org.apache.hadoop.hbase.io.encoding.DataBlockEncoding;
+import org.apache.hadoop.hbase.util.AbstractHBaseTool;
+import org.apache.hadoop.hbase.util.Bytes;
+import org.apache.yetus.audience.InterfaceAudience;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import org.apache.hbase.thirdparty.org.apache.commons.cli.CommandLine;
+
+@InterfaceAudience.LimitedPrivate(HBaseInterfaceAudience.TOOLS)
+public class DataBlockEncodingValidator extends AbstractHBaseTool {
+
+  private static final Logger LOG = LoggerFactory.getLogger(DataBlockEncodingValidator.class);
+  private static final byte[] DATA_BLOCK_ENCODING = Bytes.toBytes("DATA_BLOCK_ENCODING");
+
+  /**
+   * Check DataBlockEncodings of column families are compatible.
+   *
+   * @return number of column families with incompatible DataBlockEncoding
+   * @throws IOException if a remote or network exception occurs
+   */
+  private int validateDBE() throws IOException {
+    int incompatibilities = 0;
+
+    LOG.info("Validating Data Block Encodings");
+
+    try (Connection connection = ConnectionFactory.createConnection(getConf());
+        Admin admin = connection.getAdmin()) {
+      List<TableDescriptor> tableDescriptors = admin.listTableDescriptors();
+      String encoding = "";
+
+      for (TableDescriptor td : tableDescriptors) {
+        ColumnFamilyDescriptor[] columnFamilies = td.getColumnFamilies();
+        for (ColumnFamilyDescriptor cfd : columnFamilies) {
+          try {
+            encoding = Bytes.toString(cfd.getValue(DATA_BLOCK_ENCODING));
+            // IllegalArgumentException will be thrown if encoding is incompatible with 2.0
+            DataBlockEncoding.valueOf(encoding);
+          } catch (IllegalArgumentException e) {
+            incompatibilities++;
+            LOG.warn("Incompatible DataBlockEncoding for table: {}, cf: {}, encoding: {}",
+                td.getTableName().getNameAsString(), cfd.getNameAsString(), encoding);
+          }
+        }
+      }
+    }
+
+    if (incompatibilities > 0) {
+      LOG.warn("There are {} column families with incompatible Data Block Encodings. Do not "
+          + "upgrade until these encodings are converted to a supported one.", incompatibilities);
+      LOG.warn("Check http://hbase.apache.org/book.html#upgrade2.0.prefix-tree.removed "
+          + "for instructions.");
+    } else {
+      LOG.info("The used Data Block Encodings are compatible with HBase 2.0.");
+    }
+
+    return incompatibilities;
+  }
+
+  @Override
+  protected void printUsage() {
+    String header = "hbase " + PreUpgradeValidator.TOOL_NAME + " " +
+        PreUpgradeValidator.VALIDATE_DBE_NAME;
+    printUsage(header, null, "");
+  }
+
+  @Override
+  protected void addOptions() {
+  }
+
+  @Override
+  protected void processOptions(CommandLine cmd) {
+  }
+
+  @Override
+  protected int doWork() throws Exception {
+    return (validateDBE() == 0) ? EXIT_SUCCESS : EXIT_FAILURE;
+  }
+}

hbase-server/src/main/java/org/apache/hadoop/hbase/tool/PreUpgradeValidator.java

@@ -18,111 +18,99 @@
  */
 package org.apache.hadoop.hbase.tool;
 
-import java.io.IOException;
-import java.util.List;
+import java.util.Arrays;
 
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.hbase.HBaseConfiguration;
 import org.apache.hadoop.hbase.HBaseInterfaceAudience;
-import org.apache.hadoop.hbase.client.Admin;
-import org.apache.hadoop.hbase.client.ColumnFamilyDescriptor;
-import org.apache.hadoop.hbase.client.Connection;
-import org.apache.hadoop.hbase.client.ConnectionFactory;
-import org.apache.hadoop.hbase.client.TableDescriptor;
-import org.apache.hadoop.hbase.io.encoding.DataBlockEncoding;
+import org.apache.hadoop.hbase.tool.coprocessor.CoprocessorValidator;
 import org.apache.hadoop.hbase.util.AbstractHBaseTool;
-import org.apache.hadoop.hbase.util.Bytes;
+import org.apache.hadoop.util.Tool;
+import org.apache.hadoop.util.ToolRunner;
 import org.apache.yetus.audience.InterfaceAudience;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
-import org.apache.hbase.thirdparty.org.apache.commons.cli.CommandLine;
-
 /**
  * Tool for validating that cluster can be upgraded from HBase 1.x to 2.0
  * <p>
  * Available validations:
  * <ul>
- * <li>all: Run all pre-upgrade validations</li>
- * <li>validateDBE: Check Data Block Encoding for column families</li>
+ * <li>validate-cp: Validates Co-processors compatibility</li>
+ * <li>validate-dbe: Check Data Block Encoding for column families</li>
  * </ul>
  * </p>
  */
 @InterfaceAudience.LimitedPrivate(HBaseInterfaceAudience.TOOLS)
-public class PreUpgradeValidator extends AbstractHBaseTool {
+public class PreUpgradeValidator implements Tool {
+  private static final Logger LOG = LoggerFactory
+      .getLogger(PreUpgradeValidator.class);
 
-  public static final String NAME = "pre-upgrade";
-  private static final Logger LOG = LoggerFactory.getLogger(PreUpgradeValidator.class);
-  private static final byte[] DATA_BLOCK_ENCODING = Bytes.toBytes("DATA_BLOCK_ENCODING");
-  private boolean validateAll;
-  private boolean validateDBE;
+  public static final String TOOL_NAME = "pre-upgrade";
+  public static final String VALIDATE_CP_NAME = "validate-cp";
+  public static final String VALIDATE_DBE_NAME = "validate-dbe";
 
-  /**
-   * Check DataBlockEncodings of column families are compatible.
-   *
-   * @return number of column families with incompatible DataBlockEncoding
-   * @throws IOException if a remote or network exception occurs
-   */
-  private int validateDBE() throws IOException {
-    int incompatibilities = 0;
+  private Configuration configuration;
 
-    LOG.info("Validating Data Block Encodings");
-
-    try (Connection connection = ConnectionFactory.createConnection(getConf());
-        Admin admin = connection.getAdmin()) {
-      List<TableDescriptor> tableDescriptors = admin.listTableDescriptors();
-      String encoding = "";
-
-      for (TableDescriptor td : tableDescriptors) {
-        ColumnFamilyDescriptor[] columnFamilies = td.getColumnFamilies();
-        for (ColumnFamilyDescriptor cfd : columnFamilies) {
-          try {
-            encoding = Bytes.toString(cfd.getValue(DATA_BLOCK_ENCODING));
-            // IllegalArgumentException will be thrown if encoding is incompatible with 2.0
-            DataBlockEncoding.valueOf(encoding);
-          } catch (IllegalArgumentException e) {
-            incompatibilities++;
-            LOG.warn("Incompatible DataBlockEncoding for table: {}, cf: {}, encoding: {}",
-                td.getTableName().getNameAsString(), cfd.getNameAsString(), encoding);
-          }
-        }
-      }
-    }
-
-    if (incompatibilities > 0) {
-      LOG.warn("There are {} column families with incompatible Data Block Encodings. Do not "
-          + "upgrade until these encodings are converted to a supported one.", incompatibilities);
-      LOG.warn("Check http://hbase.apache.org/book.html#upgrade2.0.prefix-tree.removed "
-          + "for instructions.");
-    } else {
-      LOG.info("The used Data Block Encodings are compatible with HBase 2.0.");
-    }
-    return incompatibilities;
+  @Override
+  public Configuration getConf() {
+    return configuration;
   }
 
   @Override
-  protected void addOptions() {
-    addOptNoArg("all", "Run all pre-upgrade validations");
-    addOptNoArg("validateDBE", "Validate DataBlockEncodings are compatible");
+  public void setConf(Configuration conf) {
+    this.configuration = conf;
+  }
+
+  private void printUsage() {
+    System.out.println("usage: hbase " + TOOL_NAME + " command ...");
+    System.out.println("Available commands:");
+    System.out.printf(" %-12s Validate co-processors are compatible with HBase%n",
+        VALIDATE_CP_NAME);
+    System.out.printf(" %-12s Validate DataBlockEncoding are compatible on the cluster%n",
+        VALIDATE_DBE_NAME);
+    System.out.println("For further information, please use command -h");
   }
 
   @Override
-  protected void processOptions(CommandLine cmd) {
-    validateAll = cmd.hasOption("all");
-    validateDBE = cmd.hasOption("validateDBE");
+  public int run(String[] args) throws Exception {
+    if (args.length == 0) {
+      printUsage();
+      return AbstractHBaseTool.EXIT_FAILURE;
     }
 
-  @Override
-  protected int doWork() throws Exception {
-    boolean validationFailed = false;
-    if (validateDBE || validateAll) {
-      if (validateDBE() > 0) {
-        validationFailed = true;
-      }
+    Tool tool;
+
+    switch (args[0]) {
+      case VALIDATE_CP_NAME:
+        tool = new CoprocessorValidator();
+        break;
+      case VALIDATE_DBE_NAME:
+        tool = new DataBlockEncodingValidator();
+        break;
+      case "-h":
+        printUsage();
+        return AbstractHBaseTool.EXIT_FAILURE;
+      default:
+        System.err.println("Unknown command: " + args[0]);
+        printUsage();
+        return AbstractHBaseTool.EXIT_FAILURE;
     }
 
-    return validationFailed ? 1 : 0;
+    tool.setConf(getConf());
+    return tool.run(Arrays.copyOfRange(args, 1, args.length));
   }
 
   public static void main(String[] args) {
-    new PreUpgradeValidator().doStaticMain(args);
+    int ret;
+
+    try {
+      ret = ToolRunner.run(HBaseConfiguration.create(), new PreUpgradeValidator(), args);
+    } catch (Exception e) {
+      LOG.error("Error running command-line tool", e);
+      ret = AbstractHBaseTool.EXIT_FAILURE;
+    }
+
+    System.exit(ret);
   }
 }

hbase-server/src/main/java/org/apache/hadoop/hbase/tool/coprocessor/CoprocessorMethod.java

@@ -0,0 +1,73 @@
+/**
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.hadoop.hbase.tool.coprocessor;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Objects;
+
+import org.apache.yetus.audience.InterfaceAudience;
+
+@InterfaceAudience.Private
+public class CoprocessorMethod {
+  private final String name;
+  private final List<String> parameters;
+
+  public CoprocessorMethod(String name) {
+    this.name = name;
+
+    parameters = new ArrayList<>();
+  }
+
+  public CoprocessorMethod withParameters(String ... parameters) {
+    for (String parameter : parameters) {
+      this.parameters.add(parameter);
+    }
+
+    return this;
+  }
+
+  public CoprocessorMethod withParameters(Class<?> ... parameters) {
+    for (Class<?> parameter : parameters) {
+      this.parameters.add(parameter.getCanonicalName());
+    }
+
+    return this;
+  }
+
+  @Override
+  public boolean equals(Object obj) {
+    if (obj == this) {
+      return true;
+    } else if (!(obj instanceof CoprocessorMethod)) {
+      return false;
+    }
+
+    CoprocessorMethod other = (CoprocessorMethod)obj;
+
+    return Objects.equals(name, other.name) &&
+        Objects.equals(parameters, other.parameters);
+  }
+
+  @Override
+  public int hashCode() {
+    return Objects.hash(name, parameters);
+  }
+}

hbase-server/src/main/java/org/apache/hadoop/hbase/tool/coprocessor/CoprocessorMethods.java

@@ -0,0 +1,66 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.hadoop.hbase.tool.coprocessor;
+
+import java.lang.reflect.Method;
+import java.util.HashSet;
+import java.util.Set;
+
+import org.apache.yetus.audience.InterfaceAudience;
+
+@InterfaceAudience.Private
+public class CoprocessorMethods {
+  private final Set<CoprocessorMethod> methods;
+
+  public CoprocessorMethods() {
+    methods = new HashSet<>();
+  }
+
+  public void addMethod(String name, String ... parameters) {
+    CoprocessorMethod cpMethod = new CoprocessorMethod(name).withParameters(parameters);
+    methods.add(cpMethod);
+  }
+
+  public void addMethod(String name, Class<?> ... parameters) {
+    CoprocessorMethod cpMethod = new CoprocessorMethod(name).withParameters(parameters);
+    methods.add(cpMethod);
+  }
+
+  public void addMethod(Method method) {
+    CoprocessorMethod cpMethod = new CoprocessorMethod(method.getName())
+        .withParameters(method.getParameterTypes());
+    methods.add(cpMethod);
+  }
+
+  public boolean hasMethod(String name, String ... parameters) {
+    CoprocessorMethod method = new CoprocessorMethod(name).withParameters(parameters);
+    return methods.contains(method);
+  }
+
+  public boolean hasMethod(String name, Class<?> ... parameters) {
+    CoprocessorMethod method = new CoprocessorMethod(name).withParameters(parameters);
+    return methods.contains(method);
+  }
+
+  public boolean hasMethod(Method method) {
+    CoprocessorMethod cpMethod = new CoprocessorMethod(method.getName())
+        .withParameters(method.getParameterTypes());
+    return methods.contains(cpMethod);
+  }
+}

hbase-server/src/main/java/org/apache/hadoop/hbase/tool/coprocessor/CoprocessorValidator.java

@@ -0,0 +1,247 @@
+/**
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.hadoop.hbase.tool.coprocessor;
+
+import java.io.IOException;
+import java.lang.reflect.Method;
+import java.net.URL;
+import java.net.URLClassLoader;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import java.security.AccessController;
+import java.security.PrivilegedAction;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.jar.JarEntry;
+import java.util.jar.JarFile;
+import java.util.stream.Collectors;
+
+import org.apache.hadoop.hbase.Coprocessor;
+import org.apache.hadoop.hbase.HBaseInterfaceAudience;
+import org.apache.hadoop.hbase.tool.PreUpgradeValidator;
+import org.apache.hadoop.hbase.tool.coprocessor.CoprocessorViolation.Severity;
+import org.apache.hadoop.hbase.util.AbstractHBaseTool;
+import org.apache.yetus.audience.InterfaceAudience;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import org.apache.hbase.thirdparty.com.google.common.annotations.VisibleForTesting;
+import org.apache.hbase.thirdparty.org.apache.commons.cli.CommandLine;
+import org.apache.hbase.thirdparty.org.apache.commons.cli.ParseException;
+
+@InterfaceAudience.LimitedPrivate(HBaseInterfaceAudience.TOOLS)
+public class CoprocessorValidator extends AbstractHBaseTool {
+  private static final Logger LOG = LoggerFactory
+      .getLogger(CoprocessorValidator.class);
+
+  private CoprocessorMethods branch1;
+  private CoprocessorMethods current;
+
+  private boolean dieOnWarnings;
+  private boolean scan;
+  private List<String> args;
+
+  public CoprocessorValidator() {
+    branch1 = new Branch1CoprocessorMethods();
+    current = new CurrentCoprocessorMethods();
+  }
+
+  /**
+   * This classloader implementation calls {@link #resolveClass(Class)}
+   * method for every loaded class. It means that some extra validation will
+   * take place <a
+   * href="https://docs.oracle.com/javase/specs/jls/se8/html/jls-12.html#jls-12.3">
+   * according to JLS</a>.
+   */
+  private static final class ResolverUrlClassLoader extends URLClassLoader {
+    private ResolverUrlClassLoader(URL[] urls) {
+      super(urls, ResolverUrlClassLoader.class.getClassLoader());
+    }
+
+    @Override
+    public Class<?> loadClass(String name) throws ClassNotFoundException {
+      return loadClass(name, true);
+    }
+  }
+
+  private ResolverUrlClassLoader createClassLoader(URL[] urls) {
+    return AccessController.doPrivileged(new PrivilegedAction<ResolverUrlClassLoader>() {
+      @Override
+      public ResolverUrlClassLoader run() {
+        return new ResolverUrlClassLoader(urls);
+      }
+    });
+  }
+
+  private void validate(ClassLoader classLoader, String className,
+      List<CoprocessorViolation> violations) {
+    LOG.debug("Validating class '{}'.", className);
+
+    try {
+      Class<?> clazz = classLoader.loadClass(className);
+
+      for (Method method : clazz.getDeclaredMethods()) {
+        LOG.trace("Validating method '{}'.", method);
+
+        if (branch1.hasMethod(method) && !current.hasMethod(method)) {
+          CoprocessorViolation violation = new CoprocessorViolation(Severity.WARNING,
+              "Method '" + method + "' was removed from new coprocessor API, "
+                  + "so it won't be called by HBase.");
+          violations.add(violation);
+        }
+      }
+    } catch (ClassNotFoundException e) {
+      CoprocessorViolation violation = new CoprocessorViolation(Severity.ERROR,
+          "No such class '" + className + "'.", e);
+      violations.add(violation);
+    } catch (RuntimeException | Error e) {
+      CoprocessorViolation violation = new CoprocessorViolation(Severity.ERROR,
+          "Could not validate class '" + className + "'.", e);
+      violations.add(violation);
+    }
+  }
+
+  public List<CoprocessorViolation> validate(ClassLoader classLoader, List<String> classNames) {
+    List<CoprocessorViolation> violations = new ArrayList<>();
+
+    for (String className : classNames) {
+      validate(classLoader, className, violations);
+    }
+
+    return violations;
+  }
+
+  public List<CoprocessorViolation> validate(List<URL> urls, List<String> classNames)
+      throws IOException {
+    URL[] urlArray = new URL[urls.size()];
+    urls.toArray(urlArray);
+
+    try (ResolverUrlClassLoader classLoader = createClassLoader(urlArray)) {
+      return validate(classLoader, classNames);
+    }
+  }
+
+  @VisibleForTesting
+  protected List<String> getJarClasses(Path path) throws IOException {
+    try (JarFile jarFile = new JarFile(path.toFile())) {
+      return jarFile.stream()
+          .map(JarEntry::getName)
+          .filter((name) -> name.endsWith(".class"))
+          .map((name) -> name.substring(0, name.length() - 6).replace('/', '.'))
+          .collect(Collectors.toList());
+    }
+  }
+
+  @VisibleForTesting
+  protected List<String> filterObservers(ClassLoader classLoader,
+      Iterable<String> classNames) throws ClassNotFoundException {
+    List<String> filteredClassNames = new ArrayList<>();
+
+    for (String className : classNames) {
+      LOG.debug("Scanning class '{}'.", className);
+
+      Class<?> clazz = classLoader.loadClass(className);
+
+      if (Coprocessor.class.isAssignableFrom(clazz)) {
+        LOG.debug("Found coprocessor class '{}'.", className);
+        filteredClassNames.add(className);
+      }
+    }
+
+    return filteredClassNames;
+  }
+
+  @Override
+  protected void printUsage() {
+    String header = "hbase " + PreUpgradeValidator.TOOL_NAME + " " +
+        PreUpgradeValidator.VALIDATE_CP_NAME + " <jar> -scan|<classes>";
+    printUsage(header, "Options:", "");
+  }
+
+  @Override
+  protected void addOptions() {
+    addOptNoArg("e", "Treat warnings as errors.");
+    addOptNoArg("scan", "Scan jar for observers.");
+  }
+
+  @Override
+  protected void processOptions(CommandLine cmd) {
+    scan = cmd.hasOption("scan");
+    dieOnWarnings = cmd.hasOption("e");
+    args = cmd.getArgList();
+  }
+
+  @Override
+  protected int doWork() throws Exception {
+    if (args.size() < 1) {
+      System.err.println("Missing jar file.");
+      printUsage();
+      return EXIT_FAILURE;
+    }
+
+    String jar = args.get(0);
+
+    if (args.size() == 1 && !scan) {
+      throw new ParseException("Missing classes or -scan option.");
+    } else if (args.size() > 1 && scan) {
+      throw new ParseException("Can't use classes with -scan option.");
+    }
+
+    Path jarPath = Paths.get(jar);
+    URL[] urls = new URL[] { jarPath.toUri().toURL() };
+
+    List<CoprocessorViolation> violations;
+
+    try (ResolverUrlClassLoader classLoader = createClassLoader(urls)) {
+      List<String> classNames;
+
+      if (scan) {
+        List<String> jarClassNames = getJarClasses(jarPath);
+        classNames = filterObservers(classLoader, jarClassNames);
+      } else {
+        classNames = args.subList(1, args.size());
+      }
+
+      violations = validate(classLoader, classNames);
+    }
+
+    boolean error = false;
+
+    for (CoprocessorViolation violation : violations) {
+      switch (violation.getSeverity()) {
+        case WARNING:
+          System.err.println("[WARNING] " + violation.getMessage());
+
+          if (dieOnWarnings) {
+            error = true;
+          }
+
+          break;
+        case ERROR:
+          System.err.println("[ERROR] " + violation.getMessage());
+          error = true;
+
+          break;
+      }
+    }
+
+    return (error) ? EXIT_FAILURE : EXIT_SUCCESS;
+  }
+}

hbase-server/src/main/java/org/apache/hadoop/hbase/tool/coprocessor/CoprocessorViolation.java

@@ -0,0 +1,56 @@
+/**
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.hadoop.hbase.tool.coprocessor;
+
+import org.apache.yetus.audience.InterfaceAudience;
+
+import org.apache.hbase.thirdparty.com.google.common.base.Throwables;
+
+@InterfaceAudience.Private
+public class CoprocessorViolation {
+  public enum Severity {
+    WARNING, ERROR
+  }
+
+  private final Severity severity;
+  private final String message;
+
+  public CoprocessorViolation(Severity severity, String message) {
+    this(severity, message, null);
+  }
+
+  public CoprocessorViolation(Severity severity, String message, Throwable t) {
+    this.severity = severity;
+
+    if (t == null) {
+      this.message = message;
+    } else {
+      this.message = message + "\n" + Throwables.getStackTraceAsString(t);
+    }
+  }
+
+  public Severity getSeverity() {
+    return severity;
+  }
+
+  public String getMessage() {
+    return message;
+  }
+}

hbase-server/src/main/java/org/apache/hadoop/hbase/tool/coprocessor/CurrentCoprocessorMethods.java

@@ -0,0 +1,47 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.hadoop.hbase.tool.coprocessor;
+
+import java.lang.reflect.Method;
+
+import org.apache.hadoop.hbase.coprocessor.BulkLoadObserver;
+import org.apache.hadoop.hbase.coprocessor.EndpointObserver;
+import org.apache.hadoop.hbase.coprocessor.MasterObserver;
+import org.apache.hadoop.hbase.coprocessor.RegionObserver;
+import org.apache.hadoop.hbase.coprocessor.RegionServerObserver;
+import org.apache.hadoop.hbase.coprocessor.WALObserver;
+import org.apache.yetus.audience.InterfaceAudience;
+
+@InterfaceAudience.Private
+public class CurrentCoprocessorMethods extends CoprocessorMethods {
+  public CurrentCoprocessorMethods() {
+    addMethods(BulkLoadObserver.class);
+    addMethods(EndpointObserver.class);
+    addMethods(MasterObserver.class);
+    addMethods(RegionObserver.class);
+    addMethods(RegionServerObserver.class);
+    addMethods(WALObserver.class);
+  }
+
+  private void addMethods(Class<?> clazz) {
+    for (Method method : clazz.getDeclaredMethods()) {
+      addMethod(method);
+    }
+  }
+}

hbase-server/src/test/java/org/apache/hadoop/hbase/tool/coprocessor/CoprocessorValidatorTest.java

@@ -0,0 +1,177 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.hadoop.hbase.tool.coprocessor;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+
+import java.io.IOException;
+import java.util.List;
+
+import org.apache.hadoop.hbase.Coprocessor;
+import org.apache.hadoop.hbase.CoprocessorEnvironment;
+import org.apache.hadoop.hbase.HBaseClassTestRule;
+import org.apache.hadoop.hbase.HRegionInfo;
+import org.apache.hadoop.hbase.HTableDescriptor;
+import org.apache.hadoop.hbase.coprocessor.MasterCoprocessorEnvironment;
+import org.apache.hadoop.hbase.coprocessor.ObserverContext;
+import org.apache.hadoop.hbase.testclassification.SmallTests;
+import org.apache.hadoop.hbase.tool.coprocessor.CoprocessorViolation.Severity;
+import org.junit.ClassRule;
+import org.junit.Test;
+import org.junit.experimental.categories.Category;
+
+import org.apache.hbase.thirdparty.com.google.common.collect.Lists;
+
+@Category({ SmallTests.class })
+@SuppressWarnings("deprecation")
+public class CoprocessorValidatorTest {
+  @ClassRule
+  public static final HBaseClassTestRule CLASS_RULE =
+      HBaseClassTestRule.forClass(CoprocessorValidatorTest.class);
+
+  private CoprocessorValidator validator;
+
+  public CoprocessorValidatorTest() {
+    validator = new CoprocessorValidator();
+  }
+
+  private static ClassLoader getClassLoader() {
+    return CoprocessorValidatorTest.class.getClassLoader();
+  }
+
+  private static String getFullClassName(String className) {
+    return CoprocessorValidatorTest.class.getName() + "$" + className;
+  }
+
+  @SuppressWarnings({"rawtypes", "unused"})
+  private static class TestObserver implements Coprocessor {
+    @Override
+    public void start(CoprocessorEnvironment env) throws IOException {
+    }
+
+    @Override
+    public void stop(CoprocessorEnvironment env) throws IOException {
+    }
+  }
+
+  @Test
+  public void testFilterObservers() throws Exception {
+    String filterObservers = getFullClassName("TestObserver");
+    List<String> classNames = Lists.newArrayList(
+        filterObservers, getClass().getName());
+    List<String> filteredClassNames = validator.filterObservers(getClassLoader(), classNames);
+
+    assertEquals(1, filteredClassNames.size());
+    assertEquals(filterObservers, filteredClassNames.get(0));
+  }
+
+  private List<CoprocessorViolation> validate(String className) {
+    ClassLoader classLoader = getClass().getClassLoader();
+    return validate(classLoader, className);
+  }
+
+  private List<CoprocessorViolation> validate(ClassLoader classLoader, String className) {
+    List<String> classNames = Lists.newArrayList(getClass().getName() + "$" + className);
+    return validator.validate(classLoader, classNames);
+  }
+
+  /*
+   * In this test case, we are try to load a not-existent class.
+   */
+  @Test
+  public void testNoSuchClass() throws IOException {
+    List<CoprocessorViolation> violations = validate("NoSuchClass");
+    assertEquals(1, violations.size());
+
+    CoprocessorViolation violation = violations.get(0);
+    assertEquals(Severity.ERROR, violation.getSeverity());
+    assertTrue(violation.getMessage().contains(
+        "java.lang.ClassNotFoundException: " +
+        "org.apache.hadoop.hbase.tool.coprocessor.CoprocessorValidatorTest$NoSuchClass"));
+  }
+
+  /*
+   * In this test case, we are validating MissingClass coprocessor, which
+   * references a missing class. With a special classloader, we prevent that
+   * class to be loaded at runtime. It simulates similar cases where a class
+   * is no more on our classpath.
+   * E.g. org.apache.hadoop.hbase.regionserver.wal.WALEdit was moved to
+   * org.apache.hadoop.hbase.wal, so class loading will fail on 2.0.
+   */
+  private static class MissingClass {
+  }
+
+  @SuppressWarnings("unused")
+  private static class MissingClassObserver {
+    public void method(MissingClass missingClass) {
+    }
+  }
+
+  private static class MissingClassClassLoader extends ClassLoader {
+    public MissingClassClassLoader() {
+      super(getClassLoader());
+    }
+
+    @Override
+    public Class<?> loadClass(String name) throws ClassNotFoundException {
+      if (name.equals(getFullClassName("MissingClass"))) {
+        throw new ClassNotFoundException(name);
+      }
+
+      return super.findClass(name);
+    }
+  }
+
+  @Test
+  public void testMissingClass() throws IOException {
+    MissingClassClassLoader missingClassClassLoader = new MissingClassClassLoader();
+    List<CoprocessorViolation> violations = validate(missingClassClassLoader,
+        "MissingClassObserver");
+    assertEquals(1, violations.size());
+
+    CoprocessorViolation violation = violations.get(0);
+    assertEquals(Severity.ERROR, violation.getSeverity());
+    assertTrue(violation.getMessage().contains(
+        "java.lang.ClassNotFoundException: " +
+        "org.apache.hadoop.hbase.tool.coprocessor.CoprocessorValidatorTest$MissingClass"));
+  }
+
+  /*
+   * ObsoleteMethod coprocessor implements preCreateTable method which has
+   * HRegionInfo parameters. In our current implementation, we pass only
+   * RegionInfo parameters, so this method won't be called by HBase at all.
+   */
+  @SuppressWarnings("unused")
+  private static class ObsoleteMethodObserver /* implements MasterObserver */ {
+    public void preCreateTable(ObserverContext<MasterCoprocessorEnvironment> ctx,
+        HTableDescriptor desc, HRegionInfo[] regions) throws IOException {
+    }
+  }
+
+  @Test
+  public void testObsoleteMethod() throws IOException {
+    List<CoprocessorViolation> violations = validate("ObsoleteMethodObserver");
+    assertEquals(1, violations.size());
+
+    CoprocessorViolation violation = violations.get(0);
+    assertEquals(Severity.WARNING, violation.getSeverity());
+    assertTrue(violation.getMessage().contains("was removed from new coprocessor API"));
+  }
+}

src/main/asciidoc/_chapters/ops_mgt.adoc

@@ -845,11 +845,39 @@ The LoadTestTool has received many updates in recent HBase releases, including s
 [[ops.pre-upgrade]]
 === Pre-Upgrade validator
 Pre-Upgrade validator tool can be used to check the cluster for known incompatibilities before upgrading from HBase 1 to HBase 2.
-To run all the checks use the `-all` flag.
 
 [source, bash]
 ----
-$ bin/hbase pre-upgrade -all
+$ bin/hbase pre-upgrade command ...
+----
+
+==== Coprocessor validation
+
+HBase supports co-processors for a long time, but the co-processor API can be changed between major releases. Co-processor validator tries to determine
+whether the old co-processors are still compatible with the actual HBase version.
+
+[source, bash]
+----
+$ bin/hbase pre-upgrade validate-cp <jar> -scan|<classes>
+Options:
+ -e      Treat warnings as errors.
+ -scan   Scan jar for observers.
+----
+
+The first parameter of the tool is the `jar` file which holds the co-processor implementation. Further parameters can be `-scan` when the tool will
+search the jar file for `Coprocessor` implementations or the `classes` can be explicitly given.
+
+The tool can report errors and warnings. Errors mean that HBase won't be able to load the coprocessor, because it is incompatible with the current version
+of HBase. Warnings mean that the co-processors can be loaded, but they won't work as expected. If `-e` option is given, then the tool will also fail
+for warnings.
+
+Please note that this tool cannot validate every aspect of jar files, it just does some static checks.
+
+For example:
+
+[source, bash]
+----
+$ bin/hbase pre-upgrade validate-cp my-coprocessor.jar MyMasterObserver MyRegionObserver
 ----
 
 ==== DataBlockEncoding validation
@@ -858,7 +886,7 @@ To verify that none of the column families are using incompatible Data Block Enc
 
 [source, bash]
 ----
-$ bin/hbase pre-upgrade -validateDBE
+$ bin/hbase pre-upgrade validate-dbe
 ----
 
 This check validates all column families and print out any incompatibilities.