What causes "Error while executing monitoring task in {}: " in SonarSource/sonarqube?

Inspect the logged exception (the `e` argument) to find the root cause; this message itself is only a wrapper

Error while executing monitoring task in

Error message

Error while executing monitoring task in {}:

What it means

MainCollector schedules each monitoring task on a ScheduledExecutorService with scheduleWithFixedDelay. Any exception thrown by a task's run() is caught and logged with this warning so the scheduler is not cancelled by an unhandled exception.

Solutions

Inspect the logged exception (the `e` argument) to find the root cause; this message itself is only a wrapper
Check connectivity to the system the failed monitoring task polls (ES, DB)
Restart/verify the web server process if the task keeps failing every period
Fix the underlying task condition; the collector will keep retrying on its period

Defensive patterns

Strategy: try-catch

Validate before calling

// verify the system each monitoring task depends on is reachable before start
assertEsReachable(); assertDbReachable();

Try / catch

try { task.run(); } catch (Exception e) { logger.warn("monitoring task {} failed", task.getClass().getSimpleName(), e); }

Prevention

Keep monitoring tasks defensive — never let exceptions escape run()
Alert on recurrence of this warning rather than ignoring it
Ensure dependencies (ES, DB) are up before starting the collector

When it happens

Trigger: Any monitoring task registered in MainCollector.start() throws an Exception during task.run(); the wrapper logs the task class simple name plus the exception.

Common situations: Elasticsearch temporarily unreachable; database hiccups during CE monitoring; transient network failures in webhooks/push-event polling tasks.

Understand the failure class

Background: "This is a bug, please report it": internal invariant violations, unreachable panics, and SNH errors explained — this error's family across 47 libraries.

Related errors

AI-assisted analysis of SonarSource/sonarqube@184c821202 (2026-09-09). Data as JSON: /api/errors/5cf80b38c71eccb1. Report an issue: GitHub.

Appendix: source

Thrown at server/sonar-webserver-monitoring/src/main/java/org/sonar/server/monitoring/MainCollector.java:56

  private ScheduledExecutorService scheduledExecutorService;

  public MainCollector(MonitoringTask[] monitoringTasks) {
    this.monitoringTasks = monitoringTasks;
  }

  @Override
  public void start() {
    this.scheduledExecutorService = Executors.newSingleThreadScheduledExecutor(
      new ThreadFactoryBuilder()
        .setDaemon(true)
        .setNameFormat(getClass().getCanonicalName() + "-thread-%d")
        .build());
    Arrays.stream(monitoringTasks).forEach(task ->
      scheduledExecutorService.scheduleWithFixedDelay(() -> {
      try {
        task.run();
      } catch (Exception e) {
        LOG.warn("Error while executing monitoring task in {}: ", task.getClass().getSimpleName(), e);
      }
    }, task.getDelay(), task.getPeriod(), MILLISECONDS));
  }

  @Override
  public void stop() {
    scheduledExecutorService.shutdown();
  }

  @VisibleForTesting
  ScheduledExecutorService getScheduledExecutorService() {
    return scheduledExecutorService;
  }
}

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