public String getExecutionEnvironmentContainerId() {
    return getMessageValue(EXEC_ENV_ID_KEY);
  }
SetExecutionEnvContainerIdMapping is used to set the processor id to execution environment id mapping information.
@param source the source of the message
@param key the key which is used to persist the message
@param executionEnvContainerId the execution environment container id
samza-core/src/main/java/org/apache/samza/coordinator/stream/messages/SetExecutionEnvContainerIdMapping.java