@Override
  public String toString() {
    return "MetricsHeader{" + "jobName='" + jobName + '\'' + ", jobId='" + jobId + '\'' + ", containerName='"
        + containerName + '\'' + ", execEnvironmentContainerId='" + execEnvironmentContainerId + '\''
        + ", samzaEpochId=" + samzaEpochId + ", source='" + source + '\'' + ", version='" + version + '\''
        + ", samzaVersion='" + samzaVersion + '\'' + ", host='" + host + '\'' + ", time=" + time + ", resetTime="
        + resetTime + '}';
  }
Epoch id for the application, which is consistent across all components of a single deployment attempt.
This may be empty, since this field was added to this class after the initial version.
samza-core/src/main/java/org/apache/samza/metrics/reporter/MetricsHeader.java