KNOX-2978 - Race condition between Service Discovery and Polling Config Analyzer

[zeroflag]

What changes were proposed in this pull request?

When a config change is detected by the Polling Config Analyzer then then the cache used by the service discovery will be cleared. If this happens when discovery is in progress then a NullPointerException will happen.

  private ServiceDetails getServiceDetails(ServiceDiscoveryConfig serviceDiscoveryConfig, ApiService service) {
    return getClusterServices(serviceDiscoveryConfig).getIfPresent(service); // <= NPE
  }

  @Override
  public void onConfigurationChange(String source, String clusterName) {
    log.clearServiceDiscoveryRepository();
    repository.clear(); // this will cause the NPE
  }

This was observed on a live cluster when certain cluster properties was changed during knox startup.

How was this patch tested?

• unit test

[smolnar82]

LGTM