docs

Author: csviri

docs/documentation/features.md

@@ -683,6 +683,18 @@ See also
 the [integration test](https://github.com/java-operator-sdk/java-operator-sdk/blob/ec37025a15046d8f409c77616110024bf32c3416/operator-framework/src/test/java/io/javaoperatorsdk/operator/sample/changenamespace/ChangeNamespaceTestReconciler.java)
 for this feature.
 
+## Leader Election
+
+In general operators are deployed with single instance running, or a single active instance running. That means 
+if multiple instances are deployed only one of the should process the events. This is achieved by configuring leader
+election. Leader election will make sure only one instance of the operator is processing events, other instances will
+start event sources, where those will populate the caches - this is beneficial for the case the instance becomes the 
+leader it will start reconcile immediately, and don't have to wait until the event sources are started and 
+caches are populated.
+
+See sample configuration in the [E2E test](https://github.com/java-operator-sdk/java-operator-sdk/blob/144947d89323f1c65de6e86bd8b9a6a8ffe714ff/sample-operators/leader-election/src/main/java/io/javaoperatorsdk/operator/sample/LeaderElectionTestOperator.java#L26-L30)
+.
+
 ## Monitoring with Micrometer
 
 ## Automatic Generation of CRDs

operator-framework-core/src/main/java/io/javaoperatorsdk/operator/Operator.java

@@ -99,6 +99,8 @@ public void start() {
       final var clientVersion = Version.clientVersion();
       log.info("Client version: {}", clientVersion);
       ExecutorServiceManager.init();
+      // first start the controller manager before leader election,
+      // the leader election would start subsequently the processor if on
       controllerManager.start(!leaderElectionManager.isLeaderElectionOn());
       leaderElectionManager.start();
     } catch (Exception e) {

operator-framework-core/src/main/java/io/javaoperatorsdk/operator/api/config/LeaderElectionConfiguration.java

@@ -9,9 +9,6 @@ public class LeaderElectionConfiguration {
   public static final Duration RENEW_DEADLINE_DEFAULT_VALUE = Duration.ofSeconds(10);
   public static final Duration RETRY_PERIOD_DEFAULT_VALUE = Duration.ofSeconds(2);
 
-  // todo discuss
-  // private boolean syncEventSources;
-
   private final String leaseName;
   private final String leaseNamespace;
   private final String identity;

sample-operators/leader-election/src/main/java/io/javaoperatorsdk/operator/sample/LeaderElectionTestOperator.java

@@ -13,7 +13,6 @@ public class LeaderElectionTestOperator {
   private static final Logger log = LoggerFactory.getLogger(LeaderElectionTestOperator.class);
 
   public static void main(String[] args) {
-    System.out.println("Starting...");
     String identity = System.getenv("POD_NAME");
     String namespace = System.getenv("POD_NAMESPACE");
 

sample-operators/leader-election/src/main/resources/log4j2.xml

@@ -10,4 +10,4 @@
             <AppenderRef ref="Console"/>
         </Root>
     </Loggers>
-</Configuration>
+</Configuration>

sample-operators/pom.xml

@@ -24,4 +24,4 @@
         <module>mysql-schema</module>
         <module>leader-election</module>
     </modules>
-</project>
+</project>