Add prometheus metrics for logs and basic jvm stats

LavalinkServer/application.yml.example

@@ -20,6 +20,11 @@ lavalink:
     bufferDurationMs: 400
     youtubePlaylistLoadLimit: 600
 
+metrics:
+  prometheus:
+    enabled: false
+    endpoint: /metrics
+
 logging:
   file:
     max-history: 30

LavalinkServer/build.gradle

@@ -41,6 +41,11 @@ dependencies {
     compile group: 'org.json', name: 'json', version: jsonOrgVersion
     compile group: 'org.springframework.boot', name: 'spring-boot-starter-web', version: springBootVersion
     compileOnly group: 'com.github.spotbugs', name: 'spotbugs-annotations', version: spotbugsAnnotationsVersion
+
+    compile group: 'io.prometheus', name: 'simpleclient', version: prometheusVersion
+    compile group: 'io.prometheus', name: 'simpleclient_hotspot', version: prometheusVersion
+    compile group: 'io.prometheus', name: 'simpleclient_logback', version: prometheusVersion
+    compile group: 'io.prometheus', name: 'simpleclient_servlet', version: prometheusVersion
 }
 
 //create a simple version file that we will be reading to create appropriate docker tags

LavalinkServer/src/main/java/lavalink/server/config/MetricsPrometheusConfigProperties.java

@@ -0,0 +1,31 @@
+package lavalink.server.config;
+
+import org.springframework.boot.context.properties.ConfigurationProperties;
+import org.springframework.stereotype.Component;
+
+/**
+ * Created by napster on 20.05.18.
+ */
+@Component
+@ConfigurationProperties("metrics.prometheus")
+public class MetricsPrometheusConfigProperties {
+
+    private boolean enabled = false;
+    private String endpoint = "";
+
+    public boolean isEnabled() {
+        return enabled;
+    }
+
+    public void setEnabled(boolean enabled) {
+        this.enabled = enabled;
+    }
+
+    public String getEndpoint() {
+        return endpoint;
+    }
+
+    public void setEndpoint(String endpoint) {
+        this.endpoint = endpoint;
+    }
+}

LavalinkServer/src/main/java/lavalink/server/metrics/PrometheusMetrics.java

@@ -0,0 +1,35 @@
+package lavalink.server.metrics;
+
+import ch.qos.logback.classic.LoggerContext;
+import io.prometheus.client.hotspot.DefaultExports;
+import io.prometheus.client.logback.InstrumentedAppender;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
+import org.springframework.stereotype.Component;
+
+/**
+ * Created by napster on 08.05.18.
+ */
+@Component
+@ConditionalOnProperty("metrics.prometheus.enabled")
+public class PrometheusMetrics {
+
+    private static final Logger log = LoggerFactory.getLogger(PrometheusMetrics.class);
+
+    public PrometheusMetrics() {
+
+        InstrumentedAppender prometheusAppender = new InstrumentedAppender();
+        //log metrics
+        final LoggerContext factory = (LoggerContext) LoggerFactory.getILoggerFactory();
+        final ch.qos.logback.classic.Logger root = factory.getLogger(Logger.ROOT_LOGGER_NAME);
+        prometheusAppender.setContext(root.getLoggerContext());
+        prometheusAppender.start();
+        root.addAppender(prometheusAppender);
+
+        //jvm (hotspot) metrics
+        DefaultExports.initialize();
+
+        log.info("Prometheus metrics set up");
+    }
+}

LavalinkServer/src/main/java/lavalink/server/metrics/PrometheusMetricsController.java

@@ -0,0 +1,60 @@
+package lavalink.server.metrics;
+
+import io.prometheus.client.CollectorRegistry;
+import io.prometheus.client.exporter.common.TextFormat;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnBean;
+import org.springframework.http.HttpStatus;
+import org.springframework.http.ResponseEntity;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.RequestMapping;
+import org.springframework.web.bind.annotation.RequestParam;
+import org.springframework.web.bind.annotation.RestController;
+
+import javax.annotation.Nullable;
+import java.io.IOException;
+import java.io.StringWriter;
+import java.io.Writer;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.HashSet;
+import java.util.Set;
+
+/**
+ * Created by napster on 18.10.17. - Copied from Quarterdeck on 20.05.2018
+ * <p>
+ * Used to expose the prometheus metrics. Some code copied from prometheus' own MetricsServlet
+ */
+@RestController
+@RequestMapping("${metrics.prometheus.endpoint:/metrics}")
+@ConditionalOnBean(PrometheusMetrics.class)
+public class PrometheusMetricsController {
+
+    private final CollectorRegistry registry;
+
+    public PrometheusMetricsController() {
+        this.registry = CollectorRegistry.defaultRegistry;
+    }
+
+    @GetMapping(produces = TextFormat.CONTENT_TYPE_004)
+    public ResponseEntity<String> getMetrics(@Nullable @RequestParam(name = "name[]", required = false) String[] includedParam)
+            throws IOException {
+        return buildAnswer(includedParam);
+    }
+
+    private ResponseEntity<String> buildAnswer(@Nullable String[] includedParam) throws IOException {
+        Set<String> params;
+        if (includedParam == null) {
+            params = Collections.emptySet();
+        } else {
+            params = new HashSet<>(Arrays.asList(includedParam));
+        }
+
+        Writer writer = new StringWriter();
+        try (writer) {
+            TextFormat.write004(writer, this.registry.filteredMetricFamilySamples(params));
+            writer.flush();
+        }
+
+        return new ResponseEntity<>(writer.toString(), HttpStatus.OK);
+    }
+}

build.gradle

@@ -53,7 +53,7 @@ subprojects {
         oshiVersion                     = '3.4.4'
         jsonOrgVersion                  = '20180130'
         spotbugsAnnotationsVersion      = '3.1.3'
-        prometheusVersion               = '0.3.0'
+        prometheusVersion               = '0.4.0'
 
         junitJupiterVersion             = '5.1.0'
         junitPlatformVersion            = '1.1.0'