@Override
    public void onCompletion(Void result, Exception exception) {
      long processingStartTimeMs = SystemTime.getInstance().milliseconds();
      metrics.getPeersSecurityRequestTimeInMs.update(processingStartTimeMs - operationStartTimeMs);
      try {
        if (exception == null) {
          securityService.postProcessRequest(restRequest,
              new SecurityPostProcessRequestCallback(restRequest, restResponseChannel, callback));
        }
      } catch (Exception e) {
        exception = e;
      } finally {
        metrics.getPeersSecurityRequestCallbackProcessingTimeInMs.update(
            SystemTime.getInstance().milliseconds() - processingStartTimeMs);
        if (exception != null) {
          callback.onCompletion(null, exception);
        }
      }
    }
If {@code exception} is null, call {@link SecurityService#postProcessRequest(RestRequest, Callback)}.
@param result The result of the request. This would be non null when the request executed successfully
@param exception The exception that was reported on execution of the request
ambry-frontend/src/main/java/com/github/ambry/frontend/GetPeersHandler.java