[CDAP-21096] Write appfabric server port to tmp file for k8s readiness probe

cdap-app-fabric/src/main/java/io/cdap/cdap/internal/app/services/AppFabricServer.java

@@ -53,8 +53,12 @@
 import io.cdap.http.AbstractHandlerHook;
 import io.cdap.http.HttpHandler;
 import io.cdap.http.NettyHttpService;
+import java.io.File;
+import java.io.IOException;
 import java.net.InetAddress;
 import java.net.InetSocketAddress;
+import java.nio.file.Files;
+import java.nio.file.Paths;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
@@ -242,6 +246,9 @@ private Cancellable startHttpService(NettyHttpService httpService) throws Except
           ResolvingDiscoverable.of(uriScheme.createDiscoverable(serviceName, socketAddress))));
     }
 
+    writeServerPortToFile(Constants.Service.APP_FABRIC_HTTP, announcePort);
+    LOG.debug("AppFabric HTTP server started.");
+
     return () -> {
       LOG.debug("Stopping AppFabric HTTP service.");
       for (Cancellable cancellable : cancellables) {
@@ -259,4 +266,12 @@ private Cancellable startHttpService(NettyHttpService httpService) throws Except
       LOG.info("AppFabric HTTP service stopped.");
     };
   }
+
+  private void writeServerPortToFile(String service, int port) throws IOException {
+    String dir = cConf.get(Constants.Service.SERVER_PORT_DIR);
+    String filename = service + ".port";
+    File file = new File(dir, filename);
+    LOG.debug("Writing server port {} to file: {}", port, file.getAbsolutePath());
+    Files.write(file.toPath(), String.valueOf(port).getBytes());
+  }
 }

cdap-app-fabric/src/test/java/io/cdap/cdap/internal/app/services/AppFabricServerTest.java

@@ -22,14 +22,17 @@
 import io.cdap.cdap.common.conf.CConfiguration;
 import io.cdap.cdap.common.conf.Constants;
 import io.cdap.cdap.common.conf.SConfiguration;
+import io.cdap.cdap.common.conf.StringUtils;
 import io.cdap.cdap.common.discovery.EndpointStrategy;
 import io.cdap.cdap.common.discovery.RandomEndpointStrategy;
 import io.cdap.cdap.common.discovery.URIScheme;
 import io.cdap.cdap.common.utils.Tasks;
 import io.cdap.cdap.internal.AppFabricTestHelper;
 import io.cdap.cdap.security.server.LdapLoginModule;
+import java.io.File;
 import java.io.IOException;
 import java.net.InetSocketAddress;
+import java.nio.file.Files;
 import java.util.concurrent.TimeUnit;
 import java.util.function.Supplier;
 import javax.net.ssl.SSLSocket;
@@ -96,4 +99,35 @@ public void testSsl() throws IOException {
       AppFabricTestHelper.shutdown();
     }
   }
+
+  @Test
+  public void testServerPortFile() throws Exception {
+    Injector injector = AppFabricTestHelper.getInjector();
+    try {
+      AppFabricServer server = injector.getInstance(AppFabricServer.class);
+      DiscoveryServiceClient discoveryServiceClient = injector.getInstance(DiscoveryServiceClient.class);
+      Service.State state = server.startAndWait();
+      Assert.assertSame(state, Service.State.RUNNING);
+
+      final EndpointStrategy endpointStrategy = new RandomEndpointStrategy(
+          () -> discoveryServiceClient.discover(Constants.Service.APP_FABRIC_HTTP));
+      Assert.assertNotNull(endpointStrategy.pick(5, TimeUnit.SECONDS));
+
+      // Check file exists and port number is in range of 0 to 65535.
+      File file = new File("/tmp/appfabric.port");
+      Assert.assertTrue("server port file doesn't exist",
+          file.exists() && !file.isDirectory());
+      byte[] bytes = Files.readAllBytes(file.toPath());
+      String content = new String(bytes);
+      Assert.assertTrue(Integer.valueOf(content) > 0);
+      Assert.assertTrue(Integer.valueOf(content) < 65535);
+
+      state = server.stopAndWait();
+      Assert.assertSame(state, Service.State.TERMINATED);
+
+      Tasks.waitFor(true, () -> endpointStrategy.pick() == null, 5, TimeUnit.SECONDS, 100, TimeUnit.MILLISECONDS);
+    } finally {
+      AppFabricTestHelper.shutdown();
+    }
+  }
 }

cdap-common/src/main/java/io/cdap/cdap/common/conf/Constants.java

@@ -158,6 +158,8 @@ public static final class Service {
     public static final String REMOTE_AGENT_SERVICE = "remote.agent.service";
     public static final String ARTIFACT_CACHE_SERVICE = "artifact.cache.service";
     public static final String RUNTIME_MONITOR_RETRY_PREFIX = "system.runtime.monitor.";
+
+    public static final String SERVER_PORT_DIR = "system.services.server.dir";
   }
 
   /**

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

@@ -6563,4 +6563,12 @@
     </description>
   </property>
 
+  <property>
+    <name>system.services.server.dir</name>
+    <value>/tmp</value>
+    <description>
+      Directory for storing files related to server for system services.
+    </description>
+  </property>
+
 </configuration>