认识Airflow的DAG

前文Airflow的第一个DAG已经跑起来了我们的第一个任务. 本文就来丰富这个任务.

回顾我们的任务内容

• 我们定义了DAG的名称为Hello-World, 这个叫dag_id,
• 补充说明description
• 定义了调度间隔schedule_interval, 这是一个cron表达式
• 引入了一个bash任务
• 有一个重要的参数default_args, 这是dag定义的参数

如何执行不同的任务

airflow里通过引入不同的operator来执行不同的操作. 目前,内置了一些:

https://github.com/apache/airflow/tree/master/airflow/operators

第三方也贡献了一些:

https://github.com/apache/airflow/tree/master/airflow/contrib/operators

还可以自己编写plugin, 制作自己的任务类型插件.

当想要使用这些插件的时候,只要引入

from airflow.operators.bash_operator import BashOperator
from airflow.operators.dummy_operator import DummyOperator
from airflow.operators.python_operator import BranchPythonOperator
from operators.rdbms_to_redis_operator import RDBMS2RedisOperator
from operators.rdbms_to_hive_operator import RDBMS2HiveOperator
from operators.hive_to_rdbms_operator import Hive2RDBMSOperator

然后填充需要的参数:

t1 = BashOperator(task_id="hello",
            bash_command="echo 'Hello World, today is {{ ds }}'",
            dag=dag)

可以参照https://github.com/apache/airflow/tree/master/airflow/example_dags 以及源码来使用这些任务插件。

如何获取任务执行日期

这个值得单独扯一篇文章, 这里简单带一下. 通过jinja模板变量可以获取任务日期.

以下几个变量用户基本够用

templated_command = """
    echo "current bizdate is: {{ ds }} "
    echo "current bizdate in number:  {{ ds_nodash }} "
    echo "7days after: {{ macros.ds_add(ds, 7)}} "
    echo "5 days ago:  {{ macros.ds_add(ds, -5) }} "
    echo "bizdate iso8601 {{ ts }} "
    echo "bizdate format:  {{ execution_date.strftime("%d-%m-%Y") }} "
    echo "bizdate 5 days ago format: {{ (execution_date - macros.timedelta(days=5)).strftime("%Y-%m-%d") }} "

"""

t1 = BashOperator(
    task_id='print_date1',
    bash_command=templated_command,
    # on_success_callback=compass_utils.success_callback(dingding_conn_id='dingding_bigdata', receivers="ryanmiao"),
    dag=dag)

执行结果日志为：

    echo "current bizdate is: 2019-09-28 "
    echo "current bizdate in number:  20190928 "
    echo "7days after: 2019-10-05 "
    echo "5 days ago:  2019-09-23 "
    echo "bizdate iso8601 2019-09-28T01:00:00+08:00 "
    echo "bizdate format:  28-09-2019 "
    echo "bizdate 5 days ago format: 2019-09-23 "

告警

任务自己跑, 跑的结果如何, 我们需要一个通知. 可以成功的时候告诉我, 也可以失败的时候告诉我.

default_args = {
    'owner': 'ryanmiao',
    'depends_on_past': False,
    'start_date': datetime(2019, 5, 1, 9),
    'email': ['ryan.miao@nf-3.com'],
    'email_on_failure': False,
    'email_on_retry': False,
    # 'on_failure_callback': compass_utils.ding_failure_callback('dingding_bigdata'),
    # 'on_success_callback': compass_utils.ding_success_callback('dingding_bigdata')
}

默认自带的email on failure邮件通知，需要在配置文件里设置email。当然，我们通常是有自己的通知服务的，还集成自己的认证之类的。所以，Airflow提供了通知回调。

on_failure_callback 一个Python函数，失败的时候执行

on_success_callback 一个Python函数，成功的时候执行

比如，我需要添加钉钉通知。

from airflow.contrib.operators.dingding_operator import DingdingOperator

def failure_callback(context):
    """
    The function that will be executed on failure.

    :param context: The context of the executed task.
    :type context: dict
    """
    message = 'AIRFLOW TASK FAILURE TIPS:\n' \
              'DAG:    {}\n' \
              'TASKS:  {}\n' \
              'Reason: {}\n' \
        .format(context['task_instance'].dag_id,
                context['task_instance'].task_id,
                context['exception'])
    return DingdingOperator(
        task_id='dingding_success_callback',
        dingding_conn_id='dingding_default',
        message_type='text',
        message=message,
        at_all=True,
    ).execute(context)

args['on_failure_callback'] = failure_callback

后台admin-connections去配置钉钉的群组token，然后这里引用connId即可。

同样的，我们可以使用http请求调用我们自己的通知服务啊，用来发邮件，打电话什么的，都可以自定义。后面介绍自定义插件来实现这种自定义通知功能。

DAG的任务依赖

dag的任务依赖定义很简单：

a >> b   b依赖a
a << b   a依赖b
a >> b >> c   依赖可以串起来
[a,b] >> c   可以依赖多个

每个依赖语句通过换行分割， 最终会组装一个完整的依赖。

DAG的一些参数

先看看源码的注释

"""
    A dag (directed acyclic graph) is a collection of tasks with directional
    dependencies. A dag also has a schedule, a start date and an end date
    (optional). For each schedule, (say daily or hourly), the DAG needs to run
    each individual tasks as their dependencies are met. Certain tasks have
    the property of depending on their own past, meaning that they can't run
    until their previous schedule (and upstream tasks) are completed.

    DAGs essentially act as namespaces for tasks. A task_id can only be
    added once to a DAG.

    :param dag_id: The id of the DAG
    :type dag_id: str
    :param description: The description for the DAG to e.g. be shown on the webserver
    :type description: str
    :param schedule_interval: Defines how often that DAG runs, this
        timedelta object gets added to your latest task instance's
        execution_date to figure out the next schedule
    :type schedule_interval: datetime.timedelta or
        dateutil.relativedelta.relativedelta or str that acts as a cron
        expression
    :param start_date: The timestamp from which the scheduler will
        attempt to backfill
    :type start_date: datetime.datetime
    :param end_date: A date beyond which your DAG won't run, leave to None
        for open ended scheduling
    :type end_date: datetime.datetime
    :param template_searchpath: This list of folders (non relative)
        defines where jinja will look for your templates. Order matters.
        Note that jinja/airflow includes the path of your DAG file by
        default
    :type template_searchpath: str or list[str]
    :param template_undefined: Template undefined type.
    :type template_undefined: jinja2.Undefined
    :param user_defined_macros: a dictionary of macros that will be exposed
        in your jinja templates. For example, passing ``dict(foo='bar')``
        to this argument allows you to ``{{ foo }}`` in all jinja
        templates related to this DAG. Note that you can pass any
        type of object here.
    :type user_defined_macros: dict
    :param user_defined_filters: a dictionary of filters that will be exposed
        in your jinja templates. For example, passing
        ``dict(hello=lambda name: 'Hello %s' % name)`` to this argument allows
        you to ``{{ 'world' | hello }}`` in all jinja templates related to
        this DAG.
    :type user_defined_filters: dict
    :param default_args: A dictionary of default parameters to be used
        as constructor keyword parameters when initialising operators.
        Note that operators have the same hook, and precede those defined
        here, meaning that if your dict contains `'depends_on_past': True`
        here and `'depends_on_past': False` in the operator's call
        `default_args`, the actual value will be `False`.
    :type default_args: dict
    :param params: a dictionary of DAG level parameters that are made
        accessible in templates, namespaced under `params`. These
        params can be overridden at the task level.
    :type params: dict
    :param concurrency: the number of task instances allowed to run
        concurrently
    :type concurrency: int
    :param max_active_runs: maximum number of active DAG runs, beyond this
        number of DAG runs in a running state, the scheduler won't create
        new active DAG runs
    :type max_active_runs: int
    :param dagrun_timeout: specify how long a DagRun should be up before
        timing out / failing, so that new DagRuns can be created. The timeout
        is only enforced for scheduled DagRuns, and only once the
        # of active DagRuns == max_active_runs.
    :type dagrun_timeout: datetime.timedelta
    :param sla_miss_callback: specify a function to call when reporting SLA
        timeouts.
    :type sla_miss_callback: types.FunctionType
    :param default_view: Specify DAG default view (tree, graph, duration,
                                                   gantt, landing_times)
    :type default_view: str
    :param orientation: Specify DAG orientation in graph view (LR, TB, RL, BT)
    :type orientation: str
    :param catchup: Perform scheduler catchup (or only run latest)? Defaults to True
    :type catchup: bool
    :param on_failure_callback: A function to be called when a DagRun of this dag fails.
        A context dictionary is passed as a single parameter to this function.
    :type on_failure_callback: callable
    :param on_success_callback: Much like the ``on_failure_callback`` except
        that it is executed when the dag succeeds.
    :type on_success_callback: callable
    :param access_control: Specify optional DAG-level permissions, e.g.,
        "{'role1': {'can_dag_read'}, 'role2': {'can_dag_read', 'can_dag_edit'}}"
    :type access_control: dict
    :param is_paused_upon_creation: Specifies if the dag is paused when created for the first time.
        If the dag exists already, this flag will be ignored. If this optional parameter
        is not specified, the global config setting will be used.
    :type is_paused_upon_creation: bool or None
    """

emmm， 这里就不一一拆解了，我倾向于用一个了解一个。用的时候对着看。

小结

dag的组成很简单， Python语法式的声明比起property和yaml的配置来说，更容易组织和理解。

定义好dag参数，定义任务类型Operator, 定义任务依赖就完事了。