Don't allow short-circuiting election phase if only one node configured if using ZK

2 files changed, 10 insertions, 2 deletions

diff --git a/clustercontroller-core/src/main/java/com/yahoo/vespa/clustercontroller/core/FleetController.java b/clustercontroller-core/src/main/java/com/yahoo/vespa/clustercontroller/core/FleetController.java
index 898ebe243b0..43a4209981e 100644
--- a/clustercontroller-core/src/main/java/com/yahoo/vespa/clustercontroller/core/FleetController.java
+++ b/clustercontroller-core/src/main/java/com/yahoo/vespa/clustercontroller/core/FleetController.java
@@ -521,6 +521,7 @@ public class FleetController implements NodeStateOrHostInfoChangeHandler, NodeAd
 
         masterElectionHandler.setFleetControllerCount(options.fleetControllerCount);
         masterElectionHandler.setMasterZooKeeperCooldownPeriod(options.masterZooKeeperCooldownPeriod);
+        masterElectionHandler.setUsingZooKeeper(options.zooKeeperServerAddress != null && !options.zooKeeperServerAddress.isEmpty());
 
         if (rpcServer != null) {
             rpcServer.setMasterElectionHandler(masterElectionHandler);
diff --git a/clustercontroller-core/src/main/java/com/yahoo/vespa/clustercontroller/core/MasterElectionHandler.java b/clustercontroller-core/src/main/java/com/yahoo/vespa/clustercontroller/core/MasterElectionHandler.java
index 5f391b7b8e7..eeddf2fab75 100644
--- a/clustercontroller-core/src/main/java/com/yahoo/vespa/clustercontroller/core/MasterElectionHandler.java
+++ b/clustercontroller-core/src/main/java/com/yahoo/vespa/clustercontroller/core/MasterElectionHandler.java
@@ -25,6 +25,7 @@ public class MasterElectionHandler implements MasterInterface {
     private Map<Integer, Integer> nextMasterData;
     private long masterGoneFromZooKeeperTime; // Set to time master fleet controller disappears from zookeeper
     private long masterZooKeeperCooldownPeriod; // The period in ms that we won't take over unless master come back.
+    private boolean usingZooKeeper = false; // Unit tests may not use ZooKeeper at all.
 
     public MasterElectionHandler(int index, int totalCount, Object monitor, Timer timer) {
         this.monitor = monitor;
@@ -42,7 +43,7 @@ public class MasterElectionHandler implements MasterInterface {
 
     public void setFleetControllerCount(int count) {
         totalCount = count;
-        if (count == 1) {
+        if (count == 1 && !usingZooKeeper) {
             masterCandidate = 0;
             followers = 1;
             nextInLineCount = 0;
@@ -53,6 +54,10 @@ public class MasterElectionHandler implements MasterInterface {
         masterZooKeeperCooldownPeriod = period;
     }
 
+    public void setUsingZooKeeper(boolean usingZK) {
+        usingZooKeeper = usingZK;
+    }
+
     @Override
     public boolean isMaster() {
         Integer master = getMaster();
@@ -106,7 +111,9 @@ public class MasterElectionHandler implements MasterInterface {
 
     public boolean watchMasterElection(DatabaseHandler database,
                                        DatabaseHandler.Context dbContext) throws InterruptedException {
-        if (totalCount == 1) return false; // No point in doing master election with only one node configured to be cluster controller
+        if (totalCount == 1 && !usingZooKeeper) {
+            return false; // Allow single configured node to become master implicitly if no ZK configured
+        }
         if (nextMasterData == null) {
             if (masterCandidate == null) {
                 log.log(Level.FINEST, "Cluster controller " + index + ": No current master candidate. Waiting for data to do master election.");