public static synchronized AzureStorageContainerMetricsCollector getInstance(MetricRegistry metrics,
      VerifiableProperties properties) {
    if (instance == null) {
      instance = new AzureStorageContainerMetricsCollector(metrics, properties);
    }
    return instance;
  }
Thread-safe singleton initializer
@param metrics
@return collector instance
ambry-cloud/src/main/java/com/github/ambry/cloud/azure/AzureStorageContainerMetricsCollector.java