Deploy to Production
====================

This part of the tutorial assumes you have a server that you want to
deploy your application to. It gives an overview of how to create the
distribution file and install it, but won't go into specifics about
what server or software to use. You can set up a new environment on your
development computer to try out the instructions below, but probably
shouldn't use it for hosting a real public application. See
:doc:`/deploying/index` for a list of many different ways to host your
application.


Build and Install
-----------------

When you want to deploy your application elsewhere, you build a
distribution file. The current standard for Python distribution is the
*wheel* format, with the ``.whl`` extension. Make sure the wheel library
is installed first:

.. code-block:: none

    $ pip install wheel

Running ``setup.py`` with Python gives you a command line tool to issue
build-related commands. The ``bdist_wheel`` command will build a wheel
distribution file.

.. code-block:: none

    $ python setup.py bdist_wheel

You can find the file in ``dist/flaskr-1.0.0-py3-none-any.whl``. The
file name is the name of the project, the version, and some tags about
the file can install.

Copy this file to another machine,
:ref:`set up a new virtualenv <install-create-env>`, then install the
file with ``pip``.

.. code-block:: none

    $ pip install flaskr-1.0.0-py3-none-any.whl

Pip will install your project along with its dependencies.

Since this is a different machine, you need to run ``init-db`` again to
create the database in the instance folder.

.. code-block:: none

    $ export FLASK_APP=flaskr
    $ flask init-db

When Flask detects that it's installed (not in editable mode), it uses
a different directory for the instance folder. You can find it at
``venv/var/flaskr-instance`` instead.


Configure the Secret Key
------------------------

In the beginning of the tutorial that you gave a default value for
:data:`SECRET_KEY`. This should be changed to some random bytes in
production. Otherwise, attackers could use the public ``'dev'`` key to
modify the session cookie, or anything else that uses the secret key.

You can use the following command to output a random secret key:

.. code-block:: none

    $ python -c 'import os; print(os.urandom(16))'

    b'_5#y2L"F4Q8z\n\xec]/'

Create the ``config.py`` file in the instance folder, which the factory
will read from if it exists. Copy the generated value into it.

.. code-block:: python
    :caption: ``venv/var/flaskr-instance/config.py``

    SECRET_KEY = b'_5#y2L"F4Q8z\n\xec]/'

You can also set any other necessary configuration here, although
``SECRET_KEY`` is the only one needed for Flaskr.


Run with a Production Server
----------------------------

When running publicly rather than in development, you should not use the
built-in development server (``flask run``). The development server is
provided by Werkzeug for convenience, but is not designed to be
particularly efficient, stable, or secure.

Instead, use a production WSGI server. For example, to use `Waitress`_,
first install it in the virtual environment:

.. code-block:: none

    $ pip install waitress

You need to tell Waitress about your application, but it doesn't use
``FLASK_APP`` like ``flask run`` does. You need to tell it to import and
call the application factory to get an application object.

.. code-block:: none

    $ waitress-serve --call 'flaskr:create_app'

    Serving on http://0.0.0.0:8080

See :doc:`/deploying/index` for a list of many different ways to host
your application. Waitress is just an example, chosen for the tutorial
because it supports both Windows and Linux. There are many more WSGI
servers and deployment options that you may choose for your project.

.. _Waitress: https://docs.pylonsproject.org/projects/waitress/

Continue to :doc:`next`.