HBASE-20904 Prometheus /metrics http endpoint for monitoring

hbase-common/src/main/resources/hbase-default.xml

@@ -1786,6 +1786,14 @@ possible configurations would overwhelm and obscure the important.
       ThreadPool.
     </description>
   </property>
+  <property>
+    <name>hbase.http.metrics.servlets</name>
+    <value>jmx,prometheus</value>
+    <description>
+      Comma separated list of servlet names to enable for metrics collection. Supported
+      servlets are jmx, metrics, prometheus
+    </description>
+  </property>
   <property>
   	<name>hbase.replication.rpc.codec</name>
   	<value>org.apache.hadoop.hbase.codec.KeyValueCodecWithTags</value>

hbase-hadoop-compat/src/main/java/org/apache/hadoop/metrics2/impl/MetricsExportHelper.java

@@ -0,0 +1,40 @@
+/*
+ * 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.metrics2.impl;
+
+import java.util.Collection;
+import java.util.LinkedList;
+import java.util.List;
+import org.apache.hadoop.metrics2.MetricsRecord;
+import org.apache.hadoop.metrics2.lib.DefaultMetricsSystem;
+import org.apache.yetus.audience.InterfaceAudience;
+
+@InterfaceAudience.Private
+public class MetricsExportHelper {
+
+  public static Collection<MetricsRecord> export() {
+    MetricsSystemImpl instance = (MetricsSystemImpl) DefaultMetricsSystem.instance();
+    MetricsBuffer metricsBuffer = instance.sampleMetrics();
+    List<MetricsRecord> metrics = new LinkedList<>();
+    for (MetricsBuffer.Entry entry : metricsBuffer) {
+      entry.records().forEach(metrics::add);
+    }
+    return metrics;
+  }
+
+}

hbase-hadoop-compat/src/test/java/org/apache/hadoop/hbase/metrics/TestMetricsExportHelper.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.metrics;
+
+import java.util.Collection;
+import org.apache.hadoop.hbase.HBaseClassTestRule;
+import org.apache.hadoop.hbase.testclassification.MetricsTests;
+import org.apache.hadoop.hbase.testclassification.SmallTests;
+import org.apache.hadoop.metrics2.AbstractMetric;
+import org.apache.hadoop.metrics2.MetricsRecord;
+import org.apache.hadoop.metrics2.impl.MetricsExportHelper;
+import org.apache.hadoop.metrics2.lib.DefaultMetricsSystem;
+import org.junit.Assert;
+import org.junit.ClassRule;
+import org.junit.Test;
+import org.junit.experimental.categories.Category;
+
+@Category({ MetricsTests.class, SmallTests.class })
+public class TestMetricsExportHelper {
+
+  @ClassRule
+  public static final HBaseClassTestRule CLASS_RULE =
+    HBaseClassTestRule.forClass(TestMetricsExportHelper.class);
+
+  @Test
+  public void testExportHelper() {
+    DefaultMetricsSystem.initialize("exportHelperTestSystem");
+    DefaultMetricsSystem.instance().start();
+
+    String metricsName = "exportMetricsTestGrp";
+    String gaugeName = "exportMetricsTestGauge";
+    String counterName = "exportMetricsTestCounter";
+
+    BaseSourceImpl baseSource = new BaseSourceImpl(metricsName, "", metricsName, metricsName);
+
+    baseSource.setGauge(gaugeName, 0);
+    baseSource.incCounters(counterName, 1);
+
+    Collection<MetricsRecord> metrics = MetricsExportHelper.export();
+    DefaultMetricsSystem.instance().stop();
+
+    Assert.assertTrue(metrics.stream().anyMatch(mr -> mr.name().equals(metricsName)));
+    Assert.assertTrue(gaugeName + " is missing in the export",
+      contains(metrics, metricsName, gaugeName));
+    Assert.assertTrue(counterName + " is missing in the export",
+      contains(metrics, metricsName, counterName));
+  }
+
+  private boolean contains(Collection<MetricsRecord> metrics, String metricsName,
+    String metricName) {
+    return metrics.stream().filter(mr -> mr.name().equals(metricsName)).anyMatch(mr -> {
+      for (AbstractMetric metric : mr.metrics()) {
+        if (metric.name().equals(metricName)) return true;
+      }
+      return false;
+    });
+  }
+}

hbase-http/pom.xml

@@ -57,6 +57,19 @@
       <type>test-jar</type>
       <scope>test</scope>
     </dependency>
+    <dependency>
+      <groupId>org.apache.hbase</groupId>
+      <artifactId>hbase-metrics-api</artifactId>
+    </dependency>
+    <dependency>
+      <groupId>org.apache.hbase</groupId>
+      <artifactId>hbase-metrics</artifactId>
+      <scope>test</scope>
+    </dependency>
+    <dependency>
+      <groupId>org.apache.hbase</groupId>
+      <artifactId>hbase-hadoop-compat</artifactId>
+    </dependency>
     <!-- resource bundle only needed at build time -->
     <dependency>
       <groupId>org.apache.hbase</groupId>

hbase-http/src/main/java/org/apache/hadoop/hbase/http/HttpServer.java

@@ -53,7 +53,6 @@
 import org.apache.hadoop.fs.CommonConfigurationKeys;
 import org.apache.hadoop.hbase.HBaseInterfaceAudience;
 import org.apache.hadoop.hbase.http.conf.ConfServlet;
-import org.apache.hadoop.hbase.http.jmx.JMXJsonServlet;
 import org.apache.hadoop.hbase.http.log.LogLevel;
 import org.apache.hadoop.hbase.util.ReflectionUtils;
 import org.apache.hadoop.hbase.util.Threads;
@@ -154,6 +153,20 @@ public class HttpServer implements FilterContainer {
   public static final String NO_CACHE_FILTER = "NoCacheFilter";
   public static final String APP_DIR = "webapps";
 
+  public static final String METRIC_SERVLETS_CONF_KEY = "hbase.http.metrics.servlets";
+  public static final String METRICS_SERVLETS_DEFAULT[] = { "jmx" };
+  private static final Map<String, ServletConfig> METRIC_SERVLETS =
+    new HashMap<String, ServletConfig>() {
+      {
+        put("jmx",
+          new ServletConfig("jmx", "/jmx", "org.apache.hadoop.hbase.http.jmx.JMXJsonServlet"));
+        put("metrics",
+          new ServletConfig("metrics", "/metrics", "org.apache.hadoop.metrics.MetricsServlet"));
+        put("prometheus", new ServletConfig("prometheus", "/prometheus",
+          "org.apache.hadoop.hbase.http.prometheus.PrometheusHadoop2Servlet"));
+      }
+    };
+
   private final AccessControlList adminsAcl;
 
   protected final Server webServer;
@@ -751,16 +764,7 @@ protected void addDefaultServlets(ContextHandlerCollection contexts, Configurati
     // set up default servlets
     addPrivilegedServlet("stacks", "/stacks", StackServlet.class);
     addPrivilegedServlet("logLevel", "/logLevel", LogLevel.Servlet.class);
-    // Hadoop3 has moved completely to metrics2, and dropped support for Metrics v1's
-    // MetricsServlet (see HADOOP-12504). We'll using reflection to load if against hadoop2.
-    // Remove when we drop support for hbase on hadoop2.x.
-    try {
-      Class<?> clz = Class.forName("org.apache.hadoop.metrics.MetricsServlet");
-      addPrivilegedServlet("metrics", "/metrics", clz.asSubclass(HttpServlet.class));
-    } catch (Exception e) {
-      // do nothing
-    }
-    addPrivilegedServlet("jmx", "/jmx", JMXJsonServlet.class);
+
     // While we don't expect users to have sensitive information in their configuration, they
     // might. Give them an option to not expose the service configuration to all users.
     if (conf.getBoolean(HTTP_PRIVILEGED_CONF_KEY, HTTP_PRIVILEGED_CONF_DEFAULT)) {
@@ -784,6 +788,20 @@ protected void addDefaultServlets(ContextHandlerCollection contexts, Configurati
       LOG.info("ASYNC_PROFILER_HOME environment variable and async.profiler.home system property "
         + "not specified. Disabling /prof endpoint.");
     }
+
+    /* register metrics servlets */
+    String enabledServlets[] = conf.getStrings(METRIC_SERVLETS_CONF_KEY, METRICS_SERVLETS_DEFAULT);
+    for (String enabledServlet : enabledServlets) {
+      try {
+        ServletConfig servletConfig = METRIC_SERVLETS.get(enabledServlet);
+        Class<?> clz = Class.forName(servletConfig.getClazz());
+        addPrivilegedServlet(servletConfig.getName(), servletConfig.getPathSpec(),
+          clz.asSubclass(HttpServlet.class));
+      } catch (Exception e) {
+        /* shouldn't be fatal, so warn the user about it */
+        LOG.warn("Couldn't register the servlet " + enabledServlet, e);
+      }
+    }
   }
 
   /**

hbase-http/src/main/java/org/apache/hadoop/hbase/http/ServletConfig.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.http;
+
+import org.apache.yetus.audience.InterfaceAudience;
+
+/* pojo to hold the servlet info */
+
+@InterfaceAudience.Private
+class ServletConfig {
+  private String name;
+  private String pathSpec;
+  private String clazz;
+
+  public ServletConfig(String name, String pathSpec, String clazz) {
+    this.name = name;
+    this.pathSpec = pathSpec;
+    this.clazz = clazz;
+  }
+
+  public String getName() {
+    return name;
+  }
+
+  public String getPathSpec() {
+    return pathSpec;
+  }
+
+  public String getClazz() {
+    return clazz;
+  }
+}

hbase-http/src/main/java/org/apache/hadoop/hbase/http/prometheus/PrometheusHadoopServlet.java

@@ -0,0 +1,84 @@
+/*
+ * 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.http.prometheus;
+
+import com.google.errorprone.annotations.RestrictedApi;
+import java.io.IOException;
+import java.io.Writer;
+import java.util.Collection;
+import java.util.regex.Pattern;
+import javax.servlet.http.HttpServlet;
+import javax.servlet.http.HttpServletRequest;
+import javax.servlet.http.HttpServletResponse;
+import org.apache.commons.lang3.StringUtils;
+import org.apache.hadoop.metrics2.AbstractMetric;
+import org.apache.hadoop.metrics2.MetricType;
+import org.apache.hadoop.metrics2.MetricsRecord;
+import org.apache.hadoop.metrics2.MetricsTag;
+import org.apache.hadoop.metrics2.impl.MetricsExportHelper;
+import org.apache.yetus.audience.InterfaceAudience;
+
+@InterfaceAudience.Private
+public class PrometheusHadoopServlet extends HttpServlet {
+
+  private static final Pattern SPLIT_PATTERN =
+    Pattern.compile("(?<=[a-z])(?=[A-Z])|(?<=[A-Z])(?=([A-Z][a-z]))|\\W|(_)+");
+
+  @Override
+  protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws IOException {
+    writeMetrics(resp.getWriter());
+  }
+
+  static String toPrometheusName(String metricRecordName, String metricName) {
+    String baseName = metricRecordName + StringUtils.capitalize(metricName);
+    String[] parts = SPLIT_PATTERN.split(baseName);
+    return String.join("_", parts).toLowerCase();
+  }
+
+  /*
+   * SimpleClient for Prometheus is not used, because the format is very easy to implement and this
+   * solution doesn't add any dependencies to the project. You can check the Prometheus format here:
+   * https://prometheus.io/docs/instrumenting/exposition_formats/
+   */
+  @RestrictedApi(explanation = "Should only be called in tests", link = "",
+      allowedOnPath = ".*/src/test/.*")
+  void writeMetrics(Writer writer) throws IOException {
+    Collection<MetricsRecord> metricRecords = MetricsExportHelper.export();
+    for (MetricsRecord metricsRecord : metricRecords) {
+      for (AbstractMetric metrics : metricsRecord.metrics()) {
+        if (metrics.type() == MetricType.COUNTER || metrics.type() == MetricType.GAUGE) {
+
+          String key = toPrometheusName(metricsRecord.name(), metrics.name());
+          writer.append("# TYPE ").append(key).append(" ")
+            .append(metrics.type().toString().toLowerCase()).append("\n").append(key).append("{");
+
+          /* add tags */
+          String sep = "";
+          for (MetricsTag tag : metricsRecord.tags()) {
+            String tagName = tag.name().toLowerCase();
+            writer.append(sep).append(tagName).append("=\"").append(tag.value()).append("\"");
+            sep = ",";
+          }
+          writer.append("} ");
+          writer.append(metrics.value().toString()).append('\n');
+        }
+      }
+    }
+    writer.flush();
+  }
+}