code: private boolean isRetryable(SdkBaseException e) {
          if (e.getCause() instanceof IOException) {
              return true;
          } else if (e instanceof HttpException) {
              // Only retry on 500s.
              return ((HttpException) e).getStatusCode() / 100 == 5;
          } else {
              return false;
          }
      }
docs: Determines if the exception received when downloading the certificate is retryable or not.
  
  @param e Exception when downloading certificate from provided URL.
  @return True if it is retryable, false otherwise.