fix exception in Supervisor.start causing overlord unable to become leader (#6516)

* fix exception thrown by Supervisor.start causing overlord unable to become leader

* fix style

indexing-service/src/main/java/org/apache/druid/indexing/overlord/supervisor/SupervisorManager.java

@@ -133,7 +133,12 @@ public class SupervisorManager
       for (String id : supervisors.keySet()) {
         SupervisorSpec spec = supervisors.get(id);
         if (!(spec instanceof NoopSupervisorSpec)) {
-          createAndStartSupervisorInternal(spec, false);
+          try {
+            createAndStartSupervisorInternal(spec, false);
+          }
+          catch (Exception ex) {
+            log.error(ex, "Failed to start supervisor: [%s]", spec.getId());
+          }
         }
       }
 

indexing-service/src/test/java/org/apache/druid/indexing/overlord/supervisor/SupervisorManagerTest.java

@@ -228,6 +228,26 @@ public class SupervisorManagerTest extends EasyMockSupport
     manager.start();
   }
 
+  @Test
+  public void testStartIndividualSupervisorsFailStart()
+  {
+    Map<String, SupervisorSpec> existingSpecs = ImmutableMap.of(
+        "id1", new TestSupervisorSpec("id1", supervisor1),
+        "id3", new TestSupervisorSpec("id3", supervisor3)
+    );
+
+
+    EasyMock.expect(metadataSupervisorManager.getLatest()).andReturn(existingSpecs);
+    supervisor3.start();
+    supervisor1.start();
+    EasyMock.expectLastCall().andThrow(new RuntimeException("supervisor explosion"));
+    replayAll();
+
+    manager.start();
+
+    // if we get here, we are properly insulated from exploding supervisors
+  }
+
   @Test
   public void testStopThrowsException()
   {