Failed to extract xcom from airflow pod - Kubernetes Pod Operator

Question

While running a DAG which runs a jar using a docker image,
xcom_push=True is given which creates another container along with the docker image in a single pod.

DAG :

jar_task = KubernetesPodOperator(
    namespace='test',
    image="path to image",
    image_pull_secrets="secret",
    image_pull_policy="Always",
    node_selectors={"d-type":"na-node-group"},
    cmds=["sh","-c",..~running jar here~..],
    secrets=[secret_file],
    env_vars=environment_vars,
    labels={"k8s-app": "airflow"},
    name="airflow-pod",
    config_file=k8s_config_file,
    resources=pod.Resources(request_cpu=0.2,limit_cpu=0.5,request_memory='512Mi',limit_memory='1536Mi'),
    in_cluster=False,
    task_id="run_jar",
    is_delete_operator_pod=True,
    get_logs=True,
    xcom_push=True,
    dag=dag)

Here are the errors when the JAR is executed successfully..

    [2018-11-27 11:37:21,605] {{logging_mixin.py:95}} INFO - [2018-11-27 11:37:21,605] {{pod_launcher.py:166}} INFO - Running command... cat /airflow/xcom/return.json
    [2018-11-27 11:37:21,605] {{logging_mixin.py:95}} INFO - 
    [2018-11-27 11:37:21,647] {{logging_mixin.py:95}} INFO - [2018-11-27 11:37:21,646] {{pod_launcher.py:173}} INFO - cat: can't open '/airflow/xcom/return.json': No such file or directory
    [2018-11-27 11:37:21,647] {{logging_mixin.py:95}} INFO - 
    [2018-11-27 11:37:21,647] {{logging_mixin.py:95}} INFO - [2018-11-27 11:37:21,647] {{pod_launcher.py:166}} INFO - Running command... kill -s SIGINT 1
    [2018-11-27 11:37:21,647] {{logging_mixin.py:95}} INFO - 
    [2018-11-27 11:37:21,702] {{models.py:1760}} ERROR - Pod Launching failed: Failed to extract xcom from pod: airflow-pod-hippogriff-a4628b12
    Traceback (most recent call last):
      File "/usr/local/airflow/operators/kubernetes_pod_operator.py", line 126, in execute
        get_logs=self.get_logs)
      File "/usr/local/airflow/operators/pod_launcher.py", line 90, in run_pod
        return self._monitor_pod(pod, get_logs)
      File "/usr/local/airflow/operators/pod_launcher.py", line 110, in _monitor_pod
        result = self._extract_xcom(pod)
      File "/usr/local/airflow/operators/pod_launcher.py", line 161, in _extract_xcom
        raise AirflowException('Failed to extract xcom from pod: {}'.format(pod.name))
    airflow.exceptions.AirflowException: Failed to extract xcom from pod: airflow-pod-hippogriff-a4628b12

    During handling of the above exception, another exception occurred:

    Traceback (most recent call last):
      File "/usr/local/lib/python3.6/site-packages/airflow/models.py", line 1659, in _run_raw_task
        result = task_copy.execute(context=context)
      File "/usr/local/airflow/operators/kubernetes_pod_operator.py", line 138, in execute
        raise AirflowException('Pod Launching failed: {error}'.format(error=ex))
    airflow.exceptions.AirflowException: Pod Launching failed: Failed to extract xcom from pod: airflow-pod-hippogriff-a4628b12
    [2018-11-27 11:37:21,704] {{models.py:1789}} INFO - All retries failed; marking task as FAILED

Answer 1

If xcom_push is True then KubernetesPodOperator creates one more sidecar container (airflow-xcom-sidecar) in Pod along with the base container(actual worker container). This sidecar container reads data from /airflow/xcom/return.json and returns as xcom value. So in your base container you need to write the data you want to return in /airflow/xcom/return.json file.