Docs: Discovery via DNS (#29153)

akka-docs/src/test/java/jdocs/discovery/DnsDiscoveryDocTest.java

@@ -0,0 +1,54 @@
+/*
+ * Copyright (C) 2020 Lightbend Inc. <https://www.lightbend.com>
+ */
+
+package jdocs.discovery;
+
+import akka.actor.ActorSystem;
+// #lookup-dns
+import akka.discovery.Discovery;
+import akka.discovery.ServiceDiscovery;
+// #lookup-dns
+import akka.testkit.javadsl.TestKit;
+import docs.discovery.DnsDiscoveryDocSpec;
+import org.junit.AfterClass;
+import org.junit.BeforeClass;
+import org.junit.Test;
+import org.scalatestplus.junit.JUnitSuite;
+
+import java.time.Duration;
+import java.util.concurrent.CompletionStage;
+import java.util.concurrent.TimeUnit;
+
+import static org.junit.Assert.assertFalse;
+
+@SuppressWarnings("unused")
+public class DnsDiscoveryDocTest extends JUnitSuite {
+
+  private static ActorSystem system;
+
+  @BeforeClass
+  public static void setup() {
+    system = ActorSystem.create("LeaseDocTest", DnsDiscoveryDocSpec.config());
+  }
+
+  @AfterClass
+  public static void teardown() {
+    TestKit.shutdownActorSystem(system);
+    system = null;
+  }
+
+  @Test
+  public void dnsDiscoveryShouldResolveAkkaIo() throws Exception {
+    // #lookup-dns
+
+    ServiceDiscovery discovery = Discovery.get(system).discovery();
+    // ...
+    CompletionStage<ServiceDiscovery.Resolved> result =
+        discovery.lookup("akka.io", Duration.ofMillis(500));
+    // #lookup-dns
+    ServiceDiscovery.Resolved resolved =
+        result.toCompletableFuture().get(500, TimeUnit.MILLISECONDS);
+    assertFalse(resolved.getAddresses().isEmpty());
+  }
+}