Python buildpack

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You can push your Python app to Cloud Foundry and configure your Python app to use the Python buildpack.

Push an app

Cloud Foundry automatically uses this buildpack if it detects a requirements.txt or setup.py file in the root directory of your project.

If your Cloud Foundry deployment does not have the Python Buildpack installed, or the installed version is out of date, you can use the latest version by specifying it with the -b option when you push your app. For example:

$ cf push my_app -b https://github.com/cloudfoundry/python-buildpack.git

Supported versions

You can find the list of supported Python versions in the Python buildpack release notes.

Specify a Python version

You can specify a version of the Python runtime by including it within a runtime.txt file. For example:

$ cat runtime.txt
python-3.5.2

The buildpack only supports the stable Python versions, which are listed in the manifest.yml and Python buildpack release notes.

To request the latest Python version in a patch line, replace the patch version with x: 3.6.x. To request the latest version in a minor line, replace the minor version: 3.x.

If you try to use a binary that is not currently supported, staging your app fails and you see the following error message:

Could not get translated url, exited with: DEPENDENCY_MISSING_IN_MANIFEST: ...
 !
 !     exit
 !
Staging failed: Buildpack compilation step failed

Specify a PIP version

The Python buildpack supports dependency installation using PIP when a requirements.txt file is included at the top level of your app’s directory. By default, the PIP module built into Python is used when staging your app. The version of PIP used in this case depends on which version of Python is being used.

To use the latest version of PIP, set the BP_PIP_VERSION environment variable to latest before staging your app by doing either of the following:

• Use cf set-env. See set-env in the Cloud Foundry CLI Reference Guide.
• Set the PIP version in the app manifest. See Environment Variables in App Manifest Attribute Reference.

Currently, only latest is supported when setting BP_PIP_VERSION. The buildpack does not provide multiple versions of its independent PIP dependency. You can inspect the buildpack’s releases to determine which version of PIP is currently provided. See Python buildpack releases on GitHub.

Specify a start command

The Python buildpack does not generate a default start command for your apps.

To stage with the Python buildpack and start an app, do one of the following:

• Required for Cloud Foundry v245 only: Supply a Procfile. For more information about Procfiles, see the Configuring a Production Server topic. The following example Procfile specifies gunicorn as the start command for a web app running on Gunicorn:

  web: gunicorn SERVER-NAME:APP-NAME
  

• Specify a start command with -c. The following example specifies waitress-serve as the start command for a web app running on Waitress:

  $ cf push python-app -c "waitress-serve --port=$PORT DJANGO-WEB-APP.wsgi:MY-APP"
  

• Specify a start command in the application manifest by setting the command attribute. For more information, see the Deploying with App Manifests topic.

Run the web server

The Python buildpack expects the Python app to listen to port 8080. You can use the exposed PORT variable to start the web server on the port that Cloud Foundry expects on all network interfaces.

For example, you can do the following using Flask:

if __name__ == "__main__":
  port = int(os.getenv("PORT", 8080))
  app.run(host='0.0.0.0', port=port)

The PORT variable is not visible in the GUI or the cf env MY-APP command.

Vendor app dependencies

If you are deploying in an environment that is disconnected from the Internet, your application must vendor its dependencies. For more information, see Disconnected environments in the cloudfoundry/buildpack-packager GitHub repository.

For the Python buildpack, use pip:

$ cd YOUR-APP-DIR
$ mkdir -p vendor

# vendors pip *.whl into vendor/
$ pip download -r requirements.txt --no-binary=:none: -d vendor

cf push uploads your vendored dependencies. The buildpack installs them directly from the vendor/ directory.

To ensure proper installation of dependencies, Cloud Foundry recommends binary vendored dependencies (wheels). The preceding pip download command achieves this.

Private dependency repository

To deploy apps in an environment that needs to use a private dependency repository, you have the following options:

• PIP
• Conda

PIP

To install dependencies using PIP, add the URL of the repository to the requirements.txt file in the following format:

--index-url=https://example.com/api/pypi/ext_pypi/simple
fixtures==2.0.0

If the private repository uses a custom SSL certificate that is installed on the platform, you may see an error similar to the following:

Could not fetch URL https://example.com/api/pypi/ext_pypi/simple/fixtures/:
There was a problem confirming the ssl certificate:
[SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed (_ssl.c:777) - skipping

This error occurs because pip does not use system certificates by default. To resolve this issue, set the PIP_CERT environment variable in the manifest.yml file to point to the system certificate store.

For example:

---
env:
  PIP_CERT: /etc/ssl/certs/ca-certificates.crt

Conda

To install dependencies using Conda, add a channels block to the environment.yml file.

In the channels block, list custom channels and add nodefaults. Specifying nodefaults tells Conda to only use the channels in the channels block.

For example:

channels:
  - https://conda.example.com/repo
  - nodefaults

If the private repository uses a custom SSL certificate that is installed on the platform, you may see an error similar to the following:

Error: Connection error: [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed (_ssl.c:581):

This error occurs because conda does not use system certificates by default. To resolve this issue, set the CONDA_SSL_VERIFY environment variable in the manifest.yml file to point to the system certificate store.

For example:

---
env:
  CONDA_SSL_VERIFY: /etc/ssl/certs/ca-certificates.crt

Parse environment variables

The cfenv package provides access to Cloud Foundry application environment settings by parsing all the relevant environment variables. The settings are returned as a class instance. See https://github.com/jmcarp/py-cfenv for more information.

Miniconda support (starting in buildpack version 1.5.6)

To use miniconda instead of pip for installing dependencies, place an environment.yml file in the root directory.

Pipenv support (starting in buildpack version 1.5.19)

To use Pipenv instead of pip (directly) for installing dependencies, place a Pipfile in the root directory. Easiest to let Pipenv generate this for you.

NLTK support

To use NLTK corpora in your app, you can include an nltk.txt file in the root of your application. Each line in the file specifies one dataset to download. The full list of data sets available this way can be found on the NLTK website. The id listed for the corpora on that page is the string you must include in your app’s nltk.txt.

Example nltk.txt:

brown
wordnet

Having an nltk.txt file only causes the buildpack to download the corpora. You still must specify NLTK as a dependency of your app if you want to use it to process the corpora files.

Proxy support

If you need to use a proxy to download dependencies during staging, you can set the http_proxy and https_proxy environment variables. For more information, see Using a Proxy.

BOSH configured custom trusted certificate support

Versions of Python 2.7.9 and later use certificates stored in /etc/ssl/certs. Your platform operator can configure the platform to add the custom certificates into the application container.

To configure your Python applications to make HTTP requests with this custom certificate, set the environment variable REQUESTS_CA_BUNDLE="/etc/ssl/certs/ca-certificates.crt".

Help and support

Join the #buildpacks channel in our Slack community if you need any further assistance.

For more information about using and extending the Python buildpack in Cloud Foundry, see Python buildpack.

You can find current information about this buildpack on the Python buildpack release page in GitHub.