Docs: Discovery via DNS (#29153)

akka-docs/src/test/scala/docs/discovery/DnsDiscoveryDocSpec.scala

@@ -0,0 +1,43 @@
+/*
+ * Copyright (C) 2020 Lightbend Inc. <https://www.lightbend.com>
+ */
+
+package docs.discovery
+
+import akka.testkit.AkkaSpec
+import com.typesafe.config.ConfigFactory
+
+import scala.concurrent.duration._
+import scala.concurrent.Future
+
+object DnsDiscoveryDocSpec {
+  val config = ConfigFactory.parseString("""
+    // #configure-dns
+    akka {
+      discovery {
+        method = akka-dns
+      }
+    }
+    // #configure-dns
+    """)
+}
+
+class DnsDiscoveryDocSpec extends AkkaSpec(DnsDiscoveryDocSpec.config) {
+
+  "DNS Discovery" should {
+    "find akka.io" in {
+      // #lookup-dns
+      import akka.discovery.Discovery
+      import akka.discovery.ServiceDiscovery
+
+      val discovery: ServiceDiscovery = Discovery(system).discovery
+      // ...
+      val result: Future[ServiceDiscovery.Resolved] = discovery.lookup("akka.io", resolveTimeout = 500.millis)
+      // #lookup-dns
+      val resolved = result.futureValue
+      resolved.serviceName shouldBe "akka.io"
+      resolved.addresses shouldNot be(Symbol("empty"))
+    }
+  }
+
+}