@Override public void run() {
    try {
      updateCredentialsFromProperties();
    } catch (Exception e) {
      LOGGER.error("Error loading elasticsearch credentials", e);
    }
  }
Loads username/password from credentials file.

<p><em>NOTE:</em> This implementation loops instead of using {@link java.nio.file.WatchService}.
This means that spans will drop and api failures will occur for any time remaining in the refresh
interval. A future version can tighten this by also using poll events.
zipkin-server/src/main/java/zipkin2/server/internal/elasticsearch/DynamicCredentialsFileLoader.java