public static MetricsHeader fromMap(Map<String, Object> map) {
    return new MetricsHeader(map.get(JOB_NAME).toString(),
        map.get(JOB_ID).toString(),
        map.get(CONTAINER_NAME).toString(),
        map.get(EXEC_ENV_CONTAINER_ID).toString(),
        // need to check existence for backwards compatibility with initial version of this class
        Optional.ofNullable(map.get(SAMZA_EPOCH_ID)).map(Object::toString),
        map.get(SOURCE).toString(),
        map.get(VERSION).toString(),
        map.get(SAMZA_VERSION).toString(),
        map.get(HOST).toString(),
        ((Number) map.get(TIME)).longValue(),
        ((Number) map.get(RESET_TIME)).longValue());
  }
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