Sample code for joinSeedNodes programatically #24041

akka-docs/src/main/paradox/cluster-usage.md

@@ -94,6 +94,8 @@ The source code of this sample can be found in the
   [Akka Cluster Bootstrap](https://developer.lightbend.com/docs/akka-management/current/bootstrap.html) module.
 @@@
 
+### Joining configured seed nodes
+
 You may decide if joining to the cluster should be done manually or automatically
 to configured initial contact points, so-called seed nodes. After the joining process
 the seed nodes are not special and they participate in the cluster in exactly the same
@@ -118,12 +120,6 @@ This can also be defined as Java system properties when starting the JVM using t
 -Dakka.cluster.seed-nodes.1=akka.tcp://ClusterSystem@host2:2552
 ```
 
-Instead of manually configuring seed nodes, which is useful in development or statically assigned node IPs, you may want 
-to automate the discovery of seed nodes using your cloud providers or cluster orchestrator, or some other form of service 
-discovery (such as managed DNS). The open source Akka Management library includes the 
-[Cluster Bootstrap](https://developer.lightbend.com/docs/akka-management/current/bootstrap.html) module which handles 
-just that. Please refer to its documentation for more details. 
-
 The seed nodes can be started in any order and it is not necessary to have all
 seed nodes running, but the node configured as the **first element** in the `seed-nodes`
 configuration list must be started when initially starting a cluster, otherwise the
@@ -142,12 +138,28 @@ form a new cluster instead of joining remaining nodes of the existing cluster. T
 likely not desired and should be avoided by listing several nodes as seed nodes for redundancy
 and don't stop all of them at the same time.
 
+### Automatically joining to seed nodes with Cluster Bootstrap
+
+Instead of manually configuring seed nodes, which is useful in development or statically assigned node IPs, you may want
+to automate the discovery of seed nodes using your cloud providers or cluster orchestrator, or some other form of service
+discovery (such as managed DNS). The open source Akka Management library includes the
+[Cluster Bootstrap](https://developer.lightbend.com/docs/akka-management/current/bootstrap.html) module which handles
+just that. Please refer to its documentation for more details.
+
+### Programatically joining to seed nodes with `joinSeedNodes`
+
 You may also use @scala[`Cluster(system).joinSeedNodes`]@java[`Cluster.get(system).joinSeedNodes`] to join programmatically,
 which is attractive when dynamically discovering other nodes at startup by using some external tool or API.
 When using `joinSeedNodes` you should not include the node itself except for the node that is
 supposed to be the first seed node, and that should be placed first in the parameter to
 `joinSeedNodes`.
 
+Scala
+:  @@snip [ClusterDocSpec.scala]($code$/scala/docs/cluster/ClusterDocSpec.scala) { #join-seed-nodes }
+
+Java
+:  @@snip [ClusterDocTest.java]($code$/java/jdocs/cluster/ClusterDocTest.java) { #join-seed-nodes-imports #join-seed-nodes }
+
 Unsuccessful attempts to contact seed nodes are automatically retried after the time period defined in
 configuration property `seed-node-timeout`. Unsuccessful attempt to join a specific seed node is
 automatically retried after the configured `retry-unsuccessful-join-after`. Retrying means that it

akka-docs/src/test/java/jdocs/cluster/ClusterDocTest.java

@@ -6,14 +6,21 @@ package jdocs.cluster;
 
 import akka.testkit.javadsl.TestKit;
 import com.typesafe.config.ConfigFactory;
+
+import java.util.LinkedList;
+import java.util.List;
 import java.util.Set;
 import jdocs.AbstractJavaTest;
 import org.junit.AfterClass;
 import org.junit.BeforeClass;
 import org.junit.Test;
 
-import akka.actor.ActorSystem;
+//#join-seed-nodes-imports
+import akka.actor.Address;
 import akka.cluster.Cluster;
+
+//#join-seed-nodes-imports
+import akka.actor.ActorSystem;
 import akka.cluster.Member;
 
 
@@ -57,4 +64,13 @@ public class ClusterDocTest extends AbstractJavaTest {
     //#dcAccess
   }
 
+  // compile only
+  @SuppressWarnings("unused")
+  public void demonstrateJoinSeedNodes() {
+    //#join-seed-nodes
+    final Cluster cluster = Cluster.get(system);
+    List<Address> list = new LinkedList<>(); //replace this with your method to dynamically get seed nodes
+    cluster.joinSeedNodes(list);
+    //#join-seed-nodes
+  }
 }

akka-docs/src/test/scala/docs/cluster/ClusterDocSpec.scala

@@ -5,6 +5,7 @@
 package scala.docs.cluster
 
 import akka.cluster.Cluster
+
 import akka.testkit.AkkaSpec
 import docs.CompileOnlySpec
 
@@ -41,4 +42,15 @@ class ClusterDocSpec extends AkkaSpec(ClusterDocSpec.config) with CompileOnlySpe
     }
   }
 
+  "demonstrate programatic joining to seed nodes" in compileOnlySpec {
+    //#join-seed-nodes
+    import akka.actor.Address
+    import akka.cluster.Cluster
+
+    val cluster = Cluster(system)
+    val list: List[Address] = ??? //your method to dynamically get seed nodes
+    cluster.joinSeedNodes(list)
+    //#join-seed-nodes
+  }
+
 }