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Allow loading of environment variables into the config

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This new method will pick out any environment variables with a certain
prefix and place them into the config named without the prefix. This
makes it easy to use environment variables to configure the app as is
now more popular than when Flask started.

The prefix should ensure that the environment isn't polluted and the
config isn't polluted by environment variables.

I've followed the dynaconf convention of trying to parse the
environment variable and then falling back to the raw value if parsing
fails.
This commit is contained in:
pgjones 2022-03-08 21:40:48 +00:00 • committed by David Lord
parent 425a62686f
commit 08a283af5e
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3 changed files with 94 additions and 23 deletions
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47
docs/config.rst
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@ -515,9 +515,11 @@ Or from a JSON file:
Configuring from Environment Variables
--------------------------------------
In addition to pointing to configuration files using environment variables, you
may find it useful (or necessary) to control your configuration values directly
from the environment.
In addition to pointing to configuration files using environment
variables, you may find it useful (or necessary) to control your
configuration values directly from the environment. Flask can be
instructed to load all environment variables starting with a specific
prefix into the config using :meth:`~flask.Config.from_prefixed_env`.
Environment variables can be set in the shell before starting the server:
@ -527,8 +529,8 @@ Environment variables can be set in the shell before starting the server:
.. code-block:: text
$ export SECRET_KEY="5f352379324c22463451387a0aec5d2f"
$ export MAIL_ENABLED=false
$ export FLASK_SECRET_KEY="5f352379324c22463451387a0aec5d2f"
$ export FLASK_MAIL_ENABLED=false
$ flask run
* Running on http://127.0.0.1:5000/
@ -536,8 +538,8 @@ Environment variables can be set in the shell before starting the server:
.. code-block:: text
$ set -x SECRET_KEY "5f352379324c22463451387a0aec5d2f"
$ set -x MAIL_ENABLED false
$ set -x FLASK_SECRET_KEY "5f352379324c22463451387a0aec5d2f"
$ set -x FLASK_MAIL_ENABLED false
$ flask run
* Running on http://127.0.0.1:5000/
@ -545,8 +547,8 @@ Environment variables can be set in the shell before starting the server:
.. code-block:: text
> set SECRET_KEY="5f352379324c22463451387a0aec5d2f"
> set MAIL_ENABLED=false
> set FLASK_SECRET_KEY="5f352379324c22463451387a0aec5d2f"
> set FLASK_MAIL_ENABLED=false
> flask run
* Running on http://127.0.0.1:5000/
@ -554,27 +556,26 @@ Environment variables can be set in the shell before starting the server:
.. code-block:: text
> $env:SECRET_KEY = "5f352379324c22463451387a0aec5d2f"
> $env:MAIL_ENABLED = "false"
> $env:FLASK_SECRET_KEY = "5f352379324c22463451387a0aec5d2f"
> $env:FLASK_MAIL_ENABLED = "false"
> flask run
* Running on http://127.0.0.1:5000/
While this approach is straightforward to use, it is important to remember that
environment variables are strings -- they are not automatically deserialized
into Python types.
The variables can then be loaded and accessed via the config with a
key equal to the environment variable name without the prefix i.e.
Here is an example of a configuration file that uses environment variables::
.. code-block:: python
import os
app.config.from_prefixed_env()
app.config["SECRET_KEY"] # Is "5f352379324c22463451387a0aec5d2f"
_mail_enabled = os.environ.get("MAIL_ENABLED", default="true")
MAIL_ENABLED = _mail_enabled.lower() in {"1", "t", "true"}
SECRET_KEY = os.environ.get("SECRET_KEY")
if not SECRET_KEY:
raise ValueError("No SECRET_KEY set for Flask application")
The prefix is ``FLASK_`` by default, however it is an configurable via
the ``prefix`` argument of :meth:`~flask.Config.from_prefixed_env`.
Whilst the value of any environment variable is a string, it will be
parsed before being placed into the flask config. By default the
parsing is done by json.loads, however this is configurable via the
``loads`` argument of :meth:`~flask.Config.from_prefixed_env`.
Notice that any value besides an empty string will be interpreted as a boolean
``True`` value in Python, which requires care if an environment explicitly sets