👱🏻‍♀️ Monika: Experimental OpenTelemetry support

This commit tells Monika to expose the `free_space` metric for each monitored path using the *OpenTelemetry SDK for Java*.

build

@@ -4,5 +4,5 @@ cp src/main/docker/Dockerfile target
 pushd ./target
 docker build -t monika .
 popd
-docker run -it --rm -P monika
+docker run -it --rm -P -e OTEL_JAVA_GLOBAL_AUTOCONFIGURE_ENABLED=True -e OTEL_EXPORTER_OTLP_PROTOCOL=http/protobuf -e OTEL_EXPORTER_OTLP_ENDPOINT=https://grafana.ijug.eu:8080/otlp -e OTEL_SERVICE_NAME=Monika -e OTEL_METRIC_EXPORT_INTERVAL=15000 -e OTEL_METRICS_EXPORTER=otlp -e OTEL_LOGS_EXPORTER=none -e OTEL_TRACES_EXPORTER=none monika
 

pom.xml

@@ -12,6 +12,7 @@
 		<maven.compiler.release>17</maven.compiler.release>
 		<jaxrs.version>3.1.0</jaxrs.version>
 		<jersey.version>3.1.7</jersey.version>
+		<otelsdk.version>1.39.0</otelsdk.version>
 	</properties>
 
 	<dependencyManagement>
@@ -23,6 +24,14 @@
 				<type>pom</type>
 				<scope>import</scope>
 			</dependency>
+
+			<dependency>
+				<groupId>io.opentelemetry</groupId>
+				<artifactId>opentelemetry-bom</artifactId>
+				<version>${otelsdk.version}</version>
+				<type>pom</type>
+				<scope>import</scope>
+			</dependency>
 		</dependencies>
 	</dependencyManagement>
 
@@ -50,6 +59,26 @@
 			<artifactId>jersey-netty-connector</artifactId>
 			<scope>runtime</scope>
 		</dependency>
+
+		<dependency>
+			<groupId>io.opentelemetry</groupId>
+			<artifactId>opentelemetry-api</artifactId>
+		</dependency>
+
+		<dependency>
+			<groupId>io.opentelemetry</groupId>
+			<artifactId>opentelemetry-exporter-otlp</artifactId>
+		</dependency>
+
+		<dependency>
+			<groupId>io.opentelemetry</groupId>
+			<artifactId>opentelemetry-exporter-logging</artifactId>
+		</dependency>
+
+		<dependency>
+			<groupId>io.opentelemetry</groupId>
+			<artifactId>opentelemetry-sdk-extension-autoconfigure</artifactId>
+		</dependency>
 	</dependencies>
 
 	<build>
@@ -117,6 +146,12 @@
 										<exclude>**/*.so</exclude>
 									</excludes>
 								</filter>
+								<filter>
+									<artifact>io.opentelemetry:*</artifact>
+									<includes>
+										<include>**/*</include>
+									</includes>
+								</filter>
 							</filters>
 							<transformers>
 								<transformer

src/main/java/MonikaBootstrap.java

@@ -1,9 +1,16 @@
 import static jakarta.ws.rs.core.Response.Status.Family.REDIRECTION;
 import static jakarta.ws.rs.core.Response.Status.Family.SUCCESSFUL;
 
+import io.opentelemetry.api.GlobalOpenTelemetry;
+import io.opentelemetry.api.common.AttributeKey;
+import io.opentelemetry.api.common.Attributes;
+
 import java.io.File;
+import java.io.IOException;
+import java.nio.file.Files;
 import java.nio.file.Path;
 import java.util.Arrays;
+import java.util.Collection;
 import java.util.EnumSet;
 import java.util.Map;
 import java.util.Set;
@@ -16,6 +23,32 @@
 import jakarta.ws.rs.core.UriBuilder;
 
 public class MonikaBootstrap {
+
+    private static final Collection<Path> mp;
+    static {
+        final var meter = GlobalOpenTelemetry.getMeter("eu.ijug.free_disk_space");
+        final var monitoredPaths = System.getenv("MONITORED_PATHS");
+        mp = monitoredPaths == null || monitoredPaths.isBlank() ? Set.of(Path.of("/"))
+                : Arrays.asList(monitoredPaths.split(File.pathSeparator)).stream().map(Path::of).toList();
+        assert mp != null && !mp.isEmpty() : "Monitored paths cannot be null nor empty";
+        mp.forEach(monitoredPath -> System.out.printf("Monitoring: %s%n", monitoredPath));
+        meter.gaugeBuilder("system.filesystem.free")
+            .setDescription("Free disk space (measured in percent)")
+            .setUnit("Percent")
+            .buildWithCallback(measurement -> {
+                mp.forEach(monitoredPath -> {
+                    try {
+                        final var fileStore = Files.getFileStore(monitoredPath);
+                        final var percentFree = Math.toIntExact(100 * fileStore.getUsableSpace() / fileStore.getTotalSpace());
+                        System.out.printf("%s is %d %% free%n", monitoredPath, percentFree);
+                        measurement.record(percentFree, Attributes.of(AttributeKey.stringKey("system.filesystem.mountpoint"), monitoredPath.toString()));
+                    } catch (final IOException e) {
+                        e.printStackTrace();
+                    }
+                });
+        });
+    }
+
 	public static void main(final String[] args) throws InterruptedException, ExecutionException {
 		final var port = Integer.parseInt(System.getenv().getOrDefault("IP_PORT", "8080"));
 
@@ -57,15 +90,7 @@ public Set<Class<?>> getClasses() {
 			return Set.of(MonikaResource.class);
 		}
 
-        private static final Map<String, Object> PROPERTIES;
-        static {
-            final var monitoredPaths = System.getenv("MONITORED_PATHS");
-
-            final var mp = monitoredPaths == null || monitoredPaths.isBlank() ? Set.of(Path.of("/"))
-                    : Arrays.asList(monitoredPaths.split(File.pathSeparator)).stream().map(Path::of).toList();
-            mp.forEach(monitoredPath -> System.out.printf("Monitoring: %s%n", monitoredPath));
-            PROPERTIES = Map.of("MONITORED_PATHS", mp);
-        }
+        private static final Map<String, Object> PROPERTIES = Map.of("MONITORED_PATHS", mp);
 
         @Override
         public Map<String, Object> getProperties() {
@@ -81,7 +106,7 @@ private static HEALTH checkHealth(final int port, final boolean ignoreErrors) {
 			System.out.println("HEALTHCHECK " + uri);
 			if (!EnumSet.of(SUCCESSFUL, REDIRECTION).contains(ClientBuilder.newClient().target(uri).request().get().getStatusInfo().getFamily()))
                 throw new WebApplicationException();
-            
+
 			System.out.println("HEALTHY");
 			return HEALTH.SUCCESS;
 		} catch (final Throwable t) {