Merge pull request #1602 from yue9944882/improve-leaderelection-logging

Chore: Improve leader-election logging, prints out current lock helder

Author: k8s-ci-robot

extended/src/main/java/io/kubernetes/client/extended/leaderelection/LeaderElector.java

@@ -304,11 +304,9 @@ private boolean tryAcquireOrRenew() {
 
     if (observedTimeMilliSeconds + config.getLeaseDuration().toMillis() > now.getTime()
         && !isLeader()) {
-      if (log.isDebugEnabled()) {
-        log.debug(
-            "Lock is held by {} and has not yet expired",
-            oldLeaderElectionRecord.getHolderIdentity());
-      }
+      log.debug(
+          "Lock is held by {} and has not yet expired",
+          oldLeaderElectionRecord.getHolderIdentity());
       return false;
     }
 
@@ -368,7 +366,13 @@ private void maybeReportTransition() {
     this.reportedLeader = this.observedRecord.getHolderIdentity();
 
     if (this.onNewLeaderHook != null) {
-      this.hookWorkers.submit(() -> onNewLeaderHook.accept(this.reportedLeader));
+      this.hookWorkers.submit(
+          () -> {
+            log.info(
+                "LeaderElection lock is currently held by {}",
+                this.observedRecord.getHolderIdentity());
+            onNewLeaderHook.accept(this.reportedLeader);
+          });
     }
   }
 

extended/src/test/java/io/kubernetes/client/extended/leaderelection/LeaderElectorTest.java

@@ -15,6 +15,7 @@
 import java.time.Duration;
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.TimeUnit;
+import java.util.function.Consumer;
 import org.junit.Test;
 
 /** Leader Election tests using "simulated" locks created by {@link LockSmith} */
@@ -53,11 +54,64 @@ public void testLeaderGracefulShutdown() throws Exception {
     leaderElector2.close();
   }
 
+  @Test(timeout = 20000L)
+  public void testLeaderTransitionHook() throws InterruptedException {
+    LockSmith lockSmith = new LockSmith();
+
+    CountDownLatch startBeingLeader1 = new CountDownLatch(1);
+    CountDownLatch stopBeingLeader1 = new CountDownLatch(1);
+
+    LeaderElector leaderElector1 =
+        makeAndRunLeaderElectorAsync(
+            lockSmith, "candidate1", startBeingLeader1, stopBeingLeader1, (id) -> {});
+
+    // wait for candidate1 to become leader
+    startBeingLeader1.await();
+
+    // start candidate2 and the transition hook should be called on the start
+    CountDownLatch startBeingLeader2 = new CountDownLatch(1);
+    CountDownLatch stopBeingLeader2 = new CountDownLatch(1);
+    CountDownLatch notifiedLeader = new CountDownLatch(1);
+    String expectedLeader = "candidate1";
+    LeaderElector leaderElector2 =
+        makeAndRunLeaderElectorAsync(
+            lockSmith,
+            "candidate2",
+            startBeingLeader2,
+            stopBeingLeader2,
+            (id) -> {
+              if (expectedLeader.equals(id)) {
+                notifiedLeader.countDown();
+              }
+            });
+
+    notifiedLeader.await();
+
+    // start candidate1
+    leaderElector1.close();
+
+    // ensure stopBeingLeader hook is called
+    stopBeingLeader1.await();
+
+    // wait for candidate2 to become leader
+    startBeingLeader2.await();
+  }
+
   private LeaderElector makeAndRunLeaderElectorAsync(
       LockSmith lockSmith,
       String lockIdentity,
       CountDownLatch startBeingLeader,
       CountDownLatch stopBeingLeader) {
+    return makeAndRunLeaderElectorAsync(
+        lockSmith, lockIdentity, startBeingLeader, stopBeingLeader, (id) -> {});
+  }
+
+  private LeaderElector makeAndRunLeaderElectorAsync(
+      LockSmith lockSmith,
+      String lockIdentity,
+      CountDownLatch startBeingLeader,
+      CountDownLatch stopBeingLeader,
+      Consumer<String> onNewLeaderHook) {
     LeaderElectionConfig leaderElectionConfig =
         new LeaderElectionConfig(
             lockSmith.makeLock(lockIdentity),
@@ -70,7 +124,9 @@ private LeaderElector makeAndRunLeaderElectorAsync(
         new Thread(
             () ->
                 leaderElector.run(
-                    () -> startBeingLeader.countDown(), () -> stopBeingLeader.countDown()),
+                    () -> startBeingLeader.countDown(),
+                    () -> stopBeingLeader.countDown(),
+                    onNewLeaderHook),
             String.format("%s-leader-elector-main", lockIdentity));
     thread.setDaemon(true);
     thread.start();