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Executor
========

Executors are the mechanism by which :doc:`task instances </concepts/tasks>` get run. They have a common API and are "pluggable", meaning you can swap executors based on your installation needs.

Airflow can only have one executor configured at a time; this is set by the ``executor`` option in the ``[core]``
section of :doc:`the configuration file </howto/set-config>`.

Built-in executors are referred to by name, for example:

.. code-block:: ini

    [core]
    executor = KubernetesExecutor

You can also write your own custom executors, and refer to them by their full path:

.. code-block:: ini

    [core]
    executor = my_company.executors.MyCustomExecutor

.. note::
    For more information on Airflow's configuration, see :doc:`/howto/set-config`.

If you want to check which executor is currently set, you can use the ``airflow config get-value core executor`` command:

.. code-block:: bash

    $ airflow config get-value core executor
    SequentialExecutor


Executor Types
--------------

There are two types of executor - those that run tasks *locally* (inside the ``scheduler`` process), and those that run their tasks *remotely* (usually via a pool of *workers*). Airflow comes configured with the ``SequentialExecutor`` by default, which is a local executor, and the safest option for execution, but we *strongly recommend* you change this to ``LocalExecutor`` for small, single-machine installations, or one of the remote executors for a multi-machine/cloud installation.


**Local Executors**

.. toctree::
    :maxdepth: 1

    debug
    local
    sequential

**Remote Executors**

.. toctree::
    :maxdepth: 1

    celery
    celery_kubernetes
    dask
    kubernetes
    local_kubernetes


.. note::

    Something that often confuses new users of Airflow is that they don't need to run a separate ``executor`` process. This is because the executor's logic runs *inside* the ``scheduler`` process - if you're running a scheduler, you're running the executor.