Question

在运行DAG时，该DAG使用docker映像运行jar，
提供了 xcom_push = True ，它可以在一个容器中创建另一个容器以及Docker镜像。

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)

这是成功执行JAR时的错误。

    [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

如果xcom_push为True，则KubernetesPodOperator在Pod中与基本容器（实际工作容器）一起创建一个额外的sidecar容器（airflow-xcom-sidecar）。该sidecar容器从/airflow/xcom/return.json读取数据，并作为xcom值返回。因此，您需要在基本容器中将要返回的数据写入/airflow/xcom/return.json文件中。

Answer 2

之所以发生这种情况，是因为任务执行的结果没有按KubernetesPodOperator插件所需的预期路径推送到xcom。查看Airflow信息库中的以下单元测试，以检查应如何实施（为方便起见，在下面提供了源代码片段，然后是该信息库的链接）：

    def test_xcom_push(self):
    return_value = '{"foo": "bar"\n, "buzz": 2}'
    k = KubernetesPodOperator(
        namespace='default',
        image="ubuntu:16.04",
        cmds=["bash", "-cx"],
        arguments=['echo \'{}\' > /airflow/xcom/return.json'.format(return_value)],
        labels={"foo": "bar"},
        name="test",
        task_id="task",
        xcom_push=True
    )
    self.assertEqual(k.execute(None), json.loads(return_value))

https://github.com/apache/incubator-airflow/blob/36f3bfb0619cc78698280f6ec3bc985f84e58343/tests/contrib/minikube/test_kubernetes_pod_operator.py#L321

编辑：值得一提的是，推送到xcom的结果必须是json。

Answer 3

我想指出关于xcom和KubernetesPodOperator的错误，尽管它与OP的原因不同。万一有人偶然发现这个问题，因为这是关于KPO和XCom的唯一问题。

我正在使用Google Cloud Platform（GCP） Cloud Composer ，它使用的版本比最新的Airflow版本稍旧，因此当我提到官方GitHub时，它提到使用 {{1 }} ，而旧版Airflow则使用arg do_xcom_push ！

无法从气流吊舱中提取xcom-Kubernetes Pod Operator

3 个答案: