气流 - EMR操作员中的任务实例

Question

在Airflow中,我面临的问题是我需要将其传递job_flow_id给我的一个emr步骤.我能够job_flow_id从运营商检索,但是当我要创建提交到集群的步骤时,task_instance值不正确.我有以下代码:

def issue_step(name, args):
    return [
        {
            "Name": name,
            "ActionOnFailure": "CONTINUE",
            "HadoopJarStep": {
                "Jar": "s3://....",
                "Args": args
            }
        }
    ]

dag = DAG('example',
          description='My dag',
          schedule_interval='0 8 * * 6',
          dagrun_timeout=timedelta(days=2))

try:

    create_emr = EmrCreateJobFlowOperator(
        task_id='create_job_flow',
        aws_conn_id='aws_default',        
        dag=dag
    )

    load_data_steps = issue_step('load', ['arg1', 'arg2'])

    load_data_steps[0]["HadoopJarStep"]["Args"].append('--cluster-id')
    load_data_steps[0]["HadoopJarStep"]["Args"].append(
        "{{ task_instance.xcom_pull('create_job_flow', key='return_value') }}") # the value here is not exchanged with the actual job_flow_id

    load_data = EmrAddStepsOperator(
        task_id='load_data',
        job_flow_id="{{ task_instance.xcom_pull('create_job_flow', key='return_value') }}",  # this is correctly exchanged with the job_flow_id - same for the others
        aws_conn_id='aws_default',
        steps=load_data_steps,
        dag=dag
    )

    check_load_data = EmrStepSensor(
        task_id='watch_load_data',
        job_flow_id="{{ task_instance.xcom_pull('create_job_flow', key='return_value') }}",
        step_id="{{ task_instance.xcom_pull('load_data', key='return_value')[0] }}",
        aws_conn_id='aws_default',
        dag=dag
    )

    cluster_remover = EmrTerminateJobFlowOperator(
        task_id='remove_cluster',
        job_flow_id="{{ task_instance.xcom_pull('create_job_flow', key='return_value') }}",
        aws_conn_id='aws_default',
        dag=dag
    )

    create_emr_recommendations >> load_data
    load_data >> check_load_data
    check_load_data >> cluster_remover

except AirflowException as ae:
    print ae.message

问题是,当我检查EMR,也看不到--cluster-id j-1234的load_data一步,我看--cluster-id "{{task_instance.xcom_pull('create_job_flow', key='return_value')}}",这导致我的步骤就是失败的.

如何获得step函数中的实际值？

谢谢,节日快乐

Answer 1

我发现气流存储库上有关于此的 PR .问题在于没有模板化步骤EmrAddStepsOperator.为了解决这个问题,我做了以下事情:

• 创建了一个继承自的自定义运算符 EmrAddStepsOperator
• 添加此运算符作为插件
• 在我的DAG文件中调用新运算符

这里是自定义运算符的代码和文件中的插件custom_emr_add_step_operator.py(参见下面的树)

from __future__ import division, absolute_import, print_function

from airflow.plugins_manager import AirflowPlugin
from airflow.utils import apply_defaults

from airflow.contrib.operators.emr_add_steps_operator import EmrAddStepsOperator


class CustomEmrAddStepsOperator(EmrAddStepsOperator):
    template_fields = ['job_flow_id', 'steps'] # override with steps to solve the issue above

    @apply_defaults
    def __init__(
            self,
            *args, **kwargs):
        super(CustomEmrAddStepsOperator, self).__init__(*args, **kwargs)

    def execute(self, context):
        super(CustomEmrAddStepsOperator, self).execute(context=context)


# Defining the plugin class
class CustomPlugin(AirflowPlugin):
    name = "custom_plugin"
    operators = [CustomEmrAddStepsOperator]

在我的DAG文件中,我以这种方式调用了插件

from airflow.operators import CustomEmrAddStepsOperator

我的项目和插件的结构如下所示:

??? config
?   ??? airflow.cfg
??? dags
?   ??? __init__.py
?   ??? my_dag.py
??? plugins
?   ??? __init__.py
?   ??? operators
?       ??? __init__.py
?       ??? custom_emr_add_step_operator.py
??? requirements.txt

如果您使用的是像PyCharm这样的IDE,这会引发抱怨,因为它说无法找到模块.但是当您运行Airflow时,不会出现此问题.还要记住确保在你的airflow.cfg指向正确的plugins文件夹中,以便Airflow能够读取你新创建的插件.