File-based discovery plugin integration tests (#20492)

Adds an integration test for the file-based discovery plugin
to test the plugin operates correctly and uses the hosts
configured in `unicast_hosts.txt` with a real cluster

Closes #20459

buildSrc/src/main/groovy/org/elasticsearch/gradle/test/ClusterFormationTasks.groovy

@@ -147,7 +147,6 @@ class ClusterFormationTasks {
         setup = configureStopTask(taskName(task, node, 'stopPrevious'), project, setup, node)
         setup = configureExtractTask(taskName(task, node, 'extract'), project, setup, node, configuration)
         setup = configureWriteConfigTask(taskName(task, node, 'configure'), project, setup, node, seedNode)
-        setup = configureExtraConfigFilesTask(taskName(task, node, 'extraConfig'), project, setup, node)
         setup = configureCopyPluginsTask(taskName(task, node, 'copyPlugins'), project, setup, node)
 
         // install modules
@@ -162,6 +161,10 @@ class ClusterFormationTasks {
             setup = configureInstallPluginTask(taskName(task, node, actionName), project, setup, node, plugin.getValue())
         }
 
+        // sets up any extra config files that need to be copied over to the ES instance;
+        // its run after plugins have been installed, as the extra config files may belong to plugins
+        setup = configureExtraConfigFilesTask(taskName(task, node, 'extraConfig'), project, setup, node)
+
         // extra setup commands
         for (Map.Entry<String, Object[]> command : node.config.setupCommands.entrySet()) {
             // the first argument is the actual script name, relative to home

plugins/discovery-file/build.gradle

@@ -17,6 +17,10 @@
  * under the License.
  */
 
+import org.elasticsearch.gradle.test.ClusterConfiguration
+import org.elasticsearch.gradle.test.ClusterFormationTasks
+import org.elasticsearch.gradle.test.NodeInfo
+
 esplugin {
     description 'Discovery file plugin enables unicast discovery from hosts stored in a file.'
     classname 'org.elasticsearch.discovery.file.FileBasedDiscoveryPlugin'
@@ -27,3 +31,29 @@ bundlePlugin {
         into 'config'
     }
 }
+
+task setupSeedNodeAndUnicastHostsFile(type: DefaultTask) {
+    mustRunAfter(precommit)
+}
+// setup the initial cluster with one node that will serve as the seed node
+// for unicast discovery
+ClusterConfiguration config = new ClusterConfiguration(project)
+config.clusterName = 'discovery-file-test-cluster'
+List<NodeInfo> nodes = ClusterFormationTasks.setup(project, setupSeedNodeAndUnicastHostsFile, config)
+File srcUnicastHostsFile = file('build/cluster/unicast_hosts.txt')
+
+// write the unicast_hosts.txt file to a temporary location to be used by the second cluster
+setupSeedNodeAndUnicastHostsFile.doLast {
+    // write the unicast_hosts.txt file to a temp file in the build directory
+    srcUnicastHostsFile.setText(nodes.get(0).transportUri(), 'UTF-8')
+}
+
+// second cluster, which will connect to the first via the unicast_hosts.txt file
+integTest {
+    dependsOn(setupSeedNodeAndUnicastHostsFile)
+    cluster {
+        clusterName = 'discovery-file-test-cluster'
+        extraConfigFile 'discovery-file/unicast_hosts.txt', srcUnicastHostsFile
+    }
+    finalizedBy ':plugins:discovery-file:setupSeedNodeAndUnicastHostsFile#stop'
+}

plugins/discovery-file/src/test/resources/rest-api-spec/test/discovery_file/10_basic.yaml

@@ -1,13 +1,13 @@
 # Integration tests for file-based discovery
 #
-"Discovery File loaded":
+"Ensure cluster formed successfully with discovery file":
+    # make sure both nodes joined the cluster
+    - do:
+        cluster.health:
+            wait_for_nodes: 2
+
+    # make sure the cluster was formed with the correct name
     - do:
         cluster.state: {}
 
-    # Get master node id
-    - set: { master_node: master }
-
-    - do:
-        nodes.info: {}
-
-    - match:  { nodes.$master.plugins.0.name: discovery-file  }
+    - match: { cluster_name: 'discovery-file-test-cluster' } # correct cluster name, we formed the cluster we expected to