Set minimum_master_nodes on rolling-upgrade test (#26911)

The rolling-upgrade test was only writing the "minimum_master_nodes" setting to the configuration file of the old nodes, but not the upgraded ones.

Also changes the value of "minimum_master_nodes" from "number_of_nodes" to "(number_of_nodes / 2) + 1".

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

@@ -63,13 +63,11 @@ class ClusterConfiguration {
     boolean debug = false
 
     /**
-     * if <code>true</code> each node will be configured with <tt>discovery.zen.minimum_master_nodes</tt> set
-     * to the total number of nodes in the cluster. This will also cause that each node has `0s` state recovery
-     * timeout which can lead to issues if for instance an existing clusterstate is expected to be recovered
-     * before any tests start
+     * Configuration of the setting <tt>discovery.zen.minimum_master_nodes</tt> on the nodes.
+     * In case of more than one node, this defaults to (number of nodes / 2) + 1
      */
     @Input
-    boolean useMinimumMasterNodes = true
+    Closure<Integer> minimumMasterNodes = { getNumNodes() > 1 ? getNumNodes().intdiv(2) + 1 : -1 }
 
     @Input
     String jvmArgs = "-Xms" + System.getProperty('tests.heap.size', '512m') +

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

@@ -311,13 +311,14 @@ class ClusterFormationTasks {
                 // Define a node attribute so we can test that it exists
                 'node.attr.testattr'           : 'test'
         ]
-        // we set min master nodes to the total number of nodes in the cluster and
-        // basically skip initial state recovery to allow the cluster to form using a realistic master election
-        // this means all nodes must be up, join the seed node and do a master election. This will also allow new and
-        // old nodes in the BWC case to become the master
-        if (node.config.useMinimumMasterNodes && node.config.numNodes > 1) {
-            esConfig['discovery.zen.minimum_master_nodes'] = node.config.numNodes
-            esConfig['discovery.initial_state_timeout'] = '0s' // don't wait for state.. just start up quickly
+        int minimumMasterNodes = node.config.minimumMasterNodes.call()
+        if (minimumMasterNodes > 0) {
+            esConfig['discovery.zen.minimum_master_nodes'] = minimumMasterNodes
+        }
+        if (node.config.numNodes > 1) {
+            // don't wait for state.. just start up quickly
+            // this will also allow new and old nodes in the BWC case to become the master
+            esConfig['discovery.initial_state_timeout'] = '0s'
         }
         esConfig['node.max_local_storage_nodes'] = node.config.numNodes
         esConfig['http.port'] = node.config.httpPort

qa/rolling-upgrade/build.gradle

@@ -61,6 +61,7 @@ for (Version version : wireCompatVersions) {
     distribution = 'zip'
     clusterName = 'rolling-upgrade'
     unicastTransportUri = { seedNode, node, ant -> oldClusterTest.nodes.get(0).transportUri() }
+    minimumMasterNodes = { 2 }
     /* Override the data directory so the new node always gets the node we
      * just stopped's data directory. */
     dataDir = { nodeNumber -> oldClusterTest.nodes[1].dataDir }
@@ -81,6 +82,7 @@ for (Version version : wireCompatVersions) {
     distribution = 'zip'
     clusterName = 'rolling-upgrade'
     unicastTransportUri = { seedNode, node, ant -> mixedClusterTest.nodes.get(0).transportUri() }
+    minimumMasterNodes = { 2 }
     /* Override the data directory so the new node always gets the node we
      * just stopped's data directory. */
     dataDir = { nodeNumber -> oldClusterTest.nodes[0].dataDir}