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==========
Kubernetes
==========

Kubernetes is a popular container-orchestration system for automating computer application deployment, scaling, and management.
This page shows you how to set up Python environment and exeucte PyFlink jobs in a Kubernetes cluster.


Build PyFlink Image
-------------------

It requires Python 3.6 or above with PyFlink pre-installed to be available in the docker container.
It's suggested to use Python virtual environments to set up the Python environment.
See `Create a Python virtual environment <prepare.rst#create-a-python-virtual-environment>`_ for more details on how
to prepare Python virtual environments with PyFlink installed.

You need install Python environments in the docker image with PyFlink pre-installed in advance.

To build a custom image which has Python and PyFlink prepared, you can refer to the following Dockerfile:

.. code-block:: bash

    FROM flink:1.15.2

    # install python3: it has updated Python to 3.9 in Debian 11 and so install Python 3.7 from source
    # it currently only supports Python 3.6, 3.7 and 3.8 in PyFlink officially.

    RUN apt-get update -y && \
    apt-get install -y build-essential libssl-dev zlib1g-dev libbz2-dev libffi-dev && \
    wget https://www.python.org/ftp/python/3.7.9/Python-3.7.9.tgz && \
    tar -xvf Python-3.7.9.tgz && \
    cd Python-3.7.9 && \
    ./configure --without-tests --enable-shared && \
    make -j6 && \
    make install && \
    ldconfig /usr/local/lib && \
    cd .. && rm -f Python-3.7.9.tgz && rm -rf Python-3.7.9 && \
    ln -s /usr/local/bin/python3 /usr/local/bin/python && \
    apt-get clean && \
    rm -rf /var/lib/apt/lists/*

    # install PyFlink
    RUN pip3 install apache-flink==1.15.2


Execute PyFlink jobs in application mode with Native Kubernetes
---------------------------------------------------------------

You could execute PyFlink jobs in `application mode <https://nightlies.apache.org/flink/flink-docs-stable/docs/deployment/resource-providers/native_kubernetes/#application-mode>`_ as following:

This is useful when there is already a Kubernetes cluster available and you want to execute each Flink job in a separate
Flink cluster. Flink is responsible for talking with Kubernetes and allocating and de-allocating TaskManagers depending
on the required resources.

.. code-block:: bash

    ./bin/flink run-application \
          --target kubernetes-application \
          --parallelism 8 \
          -Dkubernetes.cluster-id=<ClusterId> \
          -Dtaskmanager.memory.process.size=4096m \
          -Dkubernetes.taskmanager.cpu=2 \
          -Dtaskmanager.numberOfTaskSlots=4 \
          -Dkubernetes.container.image=<PyFlinkImageName> \
          --pyModule word_count \
          --pyFiles /opt/flink/examples/python/table/word_count.py


Execute PyFlink jobs in session mode with Native Kubernetes
-----------------------------------------------------------

You could also starting a Flink session cluster on Kubernetes and then submit PyFlink jobs to the session cluster.

The session cluster could be started as following:

.. code-block:: bash

    ./bin/kubernetes-session.sh -Dkubernetes.cluster-id=my-first-flink-cluster

Then you could submit PyFlink jobs to the session cluster as following:

.. code-block:: bash

    ./bin/flink run \
        --target kubernetes-session \
        -Dkubernetes.cluster-id=my-first-flink-cluster \
        -pyarch /path/to/venv.zip \
        -pyexec venv.zip/venv/bin/python3
        -py word_count.py

.. note::
    Option **-pyclientexec** could be used to specify a local Python executable as the job will be compiled at the
    client side. Otherwise, if it's not specified, it will use the Python environment of the current shell environment.

See `Session Mode <https://nightlies.apache.org/flink/flink-docs-stable/docs/deployment/resource-providers/native_kubernetes/#session-mode>`_
for more details about session mode of Kubernetes.


Execute PyFlink jobs with Flink Kubernetes Operator
---------------------------------------------------

See `PyFlink Example <https://github.com/apache/flink-kubernetes-operator/tree/main/examples/flink-python-example>`_ for
more details on how to execute PyFlink jobs with Flink Kubernetes Operator.