diff --git a/buildSrc/src/main/groovy/org/elasticsearch/gradle/test/ClusterConfiguration.groovy b/buildSrc/src/main/groovy/org/elasticsearch/gradle/test/ClusterConfiguration.groovy
index e8415fa66fd..fa3db32e6a0 100644
--- a/buildSrc/src/main/groovy/org/elasticsearch/gradle/test/ClusterConfiguration.groovy
+++ b/buildSrc/src/main/groovy/org/elasticsearch/gradle/test/ClusterConfiguration.groovy
@@ -110,6 +110,14 @@ class ClusterConfiguration {
         return seedNode.transportUri()
     }
 
+    /**
+     * A closure to call which returns a manually supplied list of unicast seed hosts.
+     */
+    @Input
+    Closure<List<String>> otherUnicastHostAddresses = {
+        Collections.emptyList()
+    }
+
     /**
      * A closure to call before the cluster is considered ready. The closure is passed the node info,
      * as well as a groovy AntBuilder, to enable running ant condition checks. The default wait
diff --git a/buildSrc/src/main/groovy/org/elasticsearch/gradle/test/ClusterFormationTasks.groovy b/buildSrc/src/main/groovy/org/elasticsearch/gradle/test/ClusterFormationTasks.groovy
index 2c034f6e4f4..d2b4d6b3e4c 100644
--- a/buildSrc/src/main/groovy/org/elasticsearch/gradle/test/ClusterFormationTasks.groovy
+++ b/buildSrc/src/main/groovy/org/elasticsearch/gradle/test/ClusterFormationTasks.groovy
@@ -715,8 +715,9 @@ class ClusterFormationTasks {
         wait.doLast {
 
             Collection<String> unicastHosts = new HashSet<>()
-            nodes.forEach { otherNode ->
-                String unicastHost = otherNode.config.unicastTransportUri(otherNode, null, project.ant)
+            nodes.forEach { node ->
+                unicastHosts.addAll(node.config.otherUnicastHostAddresses.call())
+                String unicastHost = node.config.unicastTransportUri(node, null, project.ant)
                 if (unicastHost != null) {
                     unicastHosts.addAll(Arrays.asList(unicastHost.split(",")))
                 }
diff --git a/qa/rolling-upgrade/build.gradle b/qa/rolling-upgrade/build.gradle
index 4e27511fe04..a75b906e123 100644
--- a/qa/rolling-upgrade/build.gradle
+++ b/qa/rolling-upgrade/build.gradle
@@ -56,7 +56,6 @@ for (Version version : bwcVersions.wireCompatible) {
     mustRunAfter(precommit)
   }
 
-  Object extension = extensions.findByName("${baseName}#oldClusterTestCluster")
   configure(extensions.findByName("${baseName}#oldClusterTestCluster")) {
     bwcVersion = version
     numBwcNodes = 3
@@ -73,12 +72,12 @@ for (Version version : bwcVersions.wireCompatible) {
     systemProperty 'tests.rest.suite', 'old_cluster'
   }
 
-  Closure configureUpgradeCluster = {String name, Task lastRunner, int stopNode, Closure unicastSeed ->
+  Closure configureUpgradeCluster = {String name, Task lastRunner, int stopNode, Closure getOtherUnicastHostAddresses ->
     configure(extensions.findByName("${baseName}#${name}")) {
       dependsOn lastRunner, "${baseName}#oldClusterTestCluster#node${stopNode}.stop"
       clusterName = 'rolling-upgrade'
-      unicastTransportUri = { seedNode, node, ant -> unicastSeed() }
-      minimumMasterNodes = { 3 }
+      otherUnicastHostAddresses = { getOtherUnicastHostAddresses() }
+      minimumMasterNodes = { 2 }
       /* Override the data directory so the new node always gets the node we
       * just stopped's data directory. */
       dataDir = { nodeNumber -> oldClusterTest.nodes[stopNode].dataDir }
@@ -91,7 +90,7 @@ for (Version version : bwcVersions.wireCompatible) {
 
   configureUpgradeCluster("oneThirdUpgradedTestCluster", oldClusterTestRunner, 0,
     // Use all running nodes as seed nodes so there is no race between pinging and the tests
-    { oldClusterTest.nodes.get(1).transportUri() + ',' + oldClusterTest.nodes.get(2).transportUri() })
+    { [oldClusterTest.nodes.get(1).transportUri(), oldClusterTest.nodes.get(2).transportUri()] })
 
   Task oneThirdUpgradedTestRunner = tasks.getByName("${baseName}#oneThirdUpgradedTestRunner")
   oneThirdUpgradedTestRunner.configure {
@@ -104,7 +103,7 @@ for (Version version : bwcVersions.wireCompatible) {
 
   configureUpgradeCluster("twoThirdsUpgradedTestCluster", oneThirdUpgradedTestRunner, 1,
     // Use all running nodes as seed nodes so there is no race between pinging and the tests
-    { oldClusterTest.nodes.get(2).transportUri() + ',' + oneThirdUpgradedTest.nodes.get(0).transportUri() })
+    { [oldClusterTest.nodes.get(2).transportUri(), oneThirdUpgradedTest.nodes.get(0).transportUri()] })
 
   Task twoThirdsUpgradedTestRunner = tasks.getByName("${baseName}#twoThirdsUpgradedTestRunner")
   twoThirdsUpgradedTestRunner.configure {
@@ -117,7 +116,7 @@ for (Version version : bwcVersions.wireCompatible) {
 
   configureUpgradeCluster("upgradedClusterTestCluster", twoThirdsUpgradedTestRunner, 2,
     // Use all running nodes as seed nodes so there is no race between pinging and the tests
-    { oneThirdUpgradedTest.nodes.get(0).transportUri() + ',' + twoThirdsUpgradedTest.nodes.get(0).transportUri() })
+    { [oneThirdUpgradedTest.nodes.get(0).transportUri(), twoThirdsUpgradedTest.nodes.get(0).transportUri()] })
 
   Task upgradedClusterTestRunner = tasks.getByName("${baseName}#upgradedClusterTestRunner")
   upgradedClusterTestRunner.configure {
diff --git a/x-pack/qa/rolling-upgrade-basic/build.gradle b/x-pack/qa/rolling-upgrade-basic/build.gradle
index c3cec6695bb..da070850864 100644
--- a/x-pack/qa/rolling-upgrade-basic/build.gradle
+++ b/x-pack/qa/rolling-upgrade-basic/build.gradle
@@ -1,9 +1,6 @@
 import org.elasticsearch.gradle.Version
-import org.elasticsearch.gradle.test.NodeInfo
 import org.elasticsearch.gradle.test.RestIntegTestTask
 
-import java.nio.charset.StandardCharsets
-
 apply plugin: 'elasticsearch.standalone-test'
 
 dependencies {
@@ -40,7 +37,6 @@ for (Version version : bwcVersions.wireCompatible) {
         bwcVersion = version
         numBwcNodes = 3
         numNodes = 3
-        minimumMasterNodes = { 3 }
         clusterName = 'rolling-upgrade-basic'
         setting 'xpack.security.enabled', 'false'
         setting 'xpack.monitoring.enabled', 'false'
@@ -54,12 +50,12 @@ for (Version version : bwcVersions.wireCompatible) {
         systemProperty 'tests.rest.suite', 'old_cluster'
     }
 
-    Closure configureUpgradeCluster = {String name, Task lastRunner, int stopNode, Closure unicastSeed ->
+    Closure configureUpgradeCluster = {String name, Task lastRunner, int stopNode, Closure getOtherUnicastHostAddresses ->
         configure(extensions.findByName("${baseName}#${name}")) {
             dependsOn lastRunner, "${baseName}#oldClusterTestCluster#node${stopNode}.stop"
             clusterName = 'rolling-upgrade-basic'
-            unicastTransportUri = { seedNode, node, ant -> unicastSeed() }
-            minimumMasterNodes = { 3 }
+            otherUnicastHostAddresses = { getOtherUnicastHostAddresses() }
+            minimumMasterNodes = { 2 }
             /* Override the data directory so the new node always gets the node we
             * just stopped's data directory. */
             dataDir = { nodeNumber -> oldClusterTest.nodes[stopNode].dataDir }
@@ -77,7 +73,7 @@ for (Version version : bwcVersions.wireCompatible) {
 
     configureUpgradeCluster("oneThirdUpgradedTestCluster", oldClusterTestRunner, 0,
         // Use all running nodes as seed nodes so there is no race between pinging and the tests
-        { oldClusterTest.nodes.get(1).transportUri() + ',' + oldClusterTest.nodes.get(2).transportUri() })
+        { [oldClusterTest.nodes.get(1).transportUri(), oldClusterTest.nodes.get(2).transportUri()] })
 
     Task oneThirdUpgradedTestRunner = tasks.getByName("${baseName}#oneThirdUpgradedTestRunner")
     oneThirdUpgradedTestRunner.configure {
@@ -90,7 +86,7 @@ for (Version version : bwcVersions.wireCompatible) {
 
     configureUpgradeCluster("twoThirdsUpgradedTestCluster", oneThirdUpgradedTestRunner, 1,
         // Use all running nodes as seed nodes so there is no race between pinging and the tests
-        { oldClusterTest.nodes.get(2).transportUri() + ',' + oneThirdUpgradedTest.nodes.get(0).transportUri() })
+        { [oldClusterTest.nodes.get(2).transportUri(), oneThirdUpgradedTest.nodes.get(0).transportUri()] })
 
     Task twoThirdsUpgradedTestRunner = tasks.getByName("${baseName}#twoThirdsUpgradedTestRunner")
     twoThirdsUpgradedTestRunner.configure {
@@ -103,7 +99,7 @@ for (Version version : bwcVersions.wireCompatible) {
 
     configureUpgradeCluster("upgradedClusterTestCluster", twoThirdsUpgradedTestRunner, 2,
         // Use all running nodes as seed nodes so there is no race between pinging and the tests
-        { oneThirdUpgradedTest.nodes.get(0).transportUri() + ',' + twoThirdsUpgradedTest.nodes.get(0).transportUri() })
+        { [oneThirdUpgradedTest.nodes.get(0).transportUri(), twoThirdsUpgradedTest.nodes.get(0).transportUri()] })
 
     Task upgradedClusterTestRunner = tasks.getByName("${baseName}#upgradedClusterTestRunner")
     upgradedClusterTestRunner.configure {
diff --git a/x-pack/qa/rolling-upgrade/build.gradle b/x-pack/qa/rolling-upgrade/build.gradle
index ca149ba7e16..8a3a322efcc 100644
--- a/x-pack/qa/rolling-upgrade/build.gradle
+++ b/x-pack/qa/rolling-upgrade/build.gradle
@@ -120,7 +120,6 @@ subprojects {
       mustRunAfter(precommit)
     }
 
-    Object extension = extensions.findByName("${baseName}#oldClusterTestCluster")
     configure(extensions.findByName("${baseName}#oldClusterTestCluster")) {
       dependsOn copyTestNodeKeystore
       if (version.before('6.3.0')) {
@@ -135,7 +134,6 @@ subprojects {
       bwcVersion = version
       numBwcNodes = 3
       numNodes = 3
-      minimumMasterNodes = { 3 }
       clusterName = 'rolling-upgrade'
       waitCondition = waitWithAuth
       setting 'xpack.monitoring.exporters._http.type', 'http'
@@ -183,13 +181,13 @@ subprojects {
       systemProperty 'tests.rest.suite', 'old_cluster'
     }
 
-    Closure configureUpgradeCluster = {String name, Task lastRunner, int stopNode, Closure unicastSeed ->
+    Closure configureUpgradeCluster = {String name, Task lastRunner, int stopNode, Closure getOtherUnicastHostAddresses ->
       configure(extensions.findByName("${baseName}#${name}")) {
         dependsOn lastRunner, "${baseName}#oldClusterTestCluster#node${stopNode}.stop"
         setupCommand 'setupTestUser', 'bin/elasticsearch-users', 'useradd', 'test_user', '-p', 'x-pack-test-password', '-r', 'superuser'
         clusterName = 'rolling-upgrade'
-        unicastTransportUri = { seedNode, node, ant -> unicastSeed() }
-        minimumMasterNodes = { 3 }
+        otherUnicastHostAddresses = { getOtherUnicastHostAddresses() }
+        minimumMasterNodes = { 2 }
         /* Override the data directory so the new node always gets the node we
         * just stopped's data directory. */
         dataDir = { nodeNumber -> oldClusterTest.nodes[stopNode].dataDir }
@@ -224,7 +222,7 @@ subprojects {
 
     configureUpgradeCluster("oneThirdUpgradedTestCluster", oldClusterTestRunner, 0,
       // Use all running nodes as seed nodes so there is no race between pinging and the tests
-      { oldClusterTest.nodes.get(1).transportUri() + ',' + oldClusterTest.nodes.get(2).transportUri() })
+      { [oldClusterTest.nodes.get(1).transportUri(), oldClusterTest.nodes.get(2).transportUri()] })
 
     Task oneThirdUpgradedTestRunner = tasks.getByName("${baseName}#oneThirdUpgradedTestRunner")
     oneThirdUpgradedTestRunner.configure {
@@ -243,7 +241,7 @@ subprojects {
 
     configureUpgradeCluster("twoThirdsUpgradedTestCluster", oneThirdUpgradedTestRunner, 1,
       // Use all running nodes as seed nodes so there is no race between pinging and the tests
-      { oldClusterTest.nodes.get(2).transportUri() + ',' + oneThirdUpgradedTest.nodes.get(0).transportUri() })
+      { [oldClusterTest.nodes.get(2).transportUri(), oneThirdUpgradedTest.nodes.get(0).transportUri()] })
 
     Task twoThirdsUpgradedTestRunner = tasks.getByName("${baseName}#twoThirdsUpgradedTestRunner")
     twoThirdsUpgradedTestRunner.configure {
@@ -256,7 +254,7 @@ subprojects {
 
     configureUpgradeCluster("upgradedClusterTestCluster", twoThirdsUpgradedTestRunner, 2,
       // Use all running nodes as seed nodes so there is no race between pinging and the tests
-      { oneThirdUpgradedTest.nodes.get(0).transportUri() + ',' + twoThirdsUpgradedTest.nodes.get(0).transportUri() })
+      { [oneThirdUpgradedTest.nodes.get(0).transportUri(), twoThirdsUpgradedTest.nodes.get(0).transportUri()] })
 
     Task upgradedClusterTestRunner = tasks.getByName("${baseName}#upgradedClusterTestRunner")
     upgradedClusterTestRunner.configure {