Python Docker image

This repository contains the source for building various versions of the Python application as a reproducible Docker image using source-to-image. Users can choose between RHEL and CentOS based builder images. The resulting image can be run using Docker.

Usage

To build a simple python-sample-app application using standalone S2I and then run the resulting image with Docker execute:

• For RHEL based image $ s2i build https://github.com/sclorg/s2i-python-container.git --context-dir=3.6/test/setup-test-app/ rhscl/python-36-rhel7 python-sample-app $ docker run -p 8080:8080 python-sample-app

• For CentOS based image $ s2i build https://github.com/sclorg/s2i-python-container.git --context-dir=3.6/test/setup-test-app/ centos/python-36-centos7 python-sample-app $ docker run -p 8080:8080 python-sample-app

Accessing the application:

$ curl 127.0.0.1:8080

Repository organization

• <python-version>

  • Dockerfile

    CentOS based Dockerfile.

  • Dockerfile.rhel7

    RHEL based Dockerfile. In order to perform build or test actions on this Dockerfile you need to run the action on a properly subscribed RHEL machine.

  • s2i/bin/

    This folder contains scripts that are run by S2I:

    • assemble

      Used to install the sources into the location where the application will be run and prepare the application for deployment (eg. installing dependencies, etc.)

    • run

      This script is responsible for running the application by using the application web server.

    • usage*

      This script prints the usage of this image.

  • contrib/

    This folder contains a file with commonly used modules.

  • test/

    This folder contains a S2I test framework with a simple server.

    • setup-test-app/

      Simple Gunicorn application used for testing purposes by the S2I test framework.

    • standalone-test-app/

      Simple standalone application used for testing purposes by the S2I test framework.

    • run

      Script that runs the S2I test framework.

Environment variables

To set these environment variables, you can place them as a key value pair into a .s2i/environment file inside your source code repository.

• APP_SCRIPT

  Used to run the application from a script file. This should be a path to a script file (defaults to app.sh unless set to null) that will be run to start the application.

• APP_FILE

  Used to run the application from a Python script. This should be a path to a Python file (defaults to app.py unless set to null) that will be passed to the Python interpreter to start the application.

• APP_MODULE

  Used to run the application with Gunicorn, as documented here. This variable specifies a WSGI callable with the pattern MODULE_NAME:VARIABLE_NAME, where MODULE_NAME is the full dotted path of a module, and VARIABLE_NAME refers to a WSGI callable inside the specified module. Gunicorn will look for a WSGI callable named application if not specified.

  If APP_MODULE is not provided, the run script will look for a wsgi.py file in your project and use it if it exists.

  If using setup.py for installing the application, the MODULE_NAME part can be read from there. For an example, see setup-test-app.

• APP_HOME

  This variable can be used to specify a sub-directory in which the application to be run is contained. The directory pointed to by this variable needs to contain wsgi.py (for Gunicorn) or manage.py (for Django).

  If APP_HOME is not provided, the assemble and run scripts will use the application's root directory.

• APP_CONFIG

  Path to a valid Python file with a Gunicorn configuration file.

• DISABLE_COLLECTSTATIC

  Set this variable to a non-empty value to inhibit the execution of 'manage.py collectstatic' during the build. This only affects Django projects.

• DISABLE_MIGRATE

  Set this variable to a non-empty value to inhibit the execution of 'manage.py migrate' when the produced image is run. This only affects Django projects.

• PIP_INDEX_URL

  Set this variable to use a custom index URL or mirror to download required packages during build process. This only affects packages listed in requirements.txt.

• UPGRADE_PIP_TO_LATEST

  Set this variable to a non-empty value to have the 'pip' program be upgraded to the most recent version before any Python packages are installed. If not set it will use whatever the default version is included by the platform for the Python version being used.

• WEB_CONCURRENCY

  Set this to change the default setting for the number of workers. By default, this is set to the number of available cores times 2.

Source repository layout

You do not need to change anything in your existing Python project's repository. However, if these files exist they will affect the behavior of the build process:

• requirements.txt

List of dependencies to be installed with pip. The format is documented here.

• setup.py

Configures various aspects of the project, including installation of dependencies, as documented here. For most projects, it is sufficient to simply use requirements.txt.

Run strategies

The Docker image produced by s2i-python executes your project in one of the following ways, in precedence order:

• Gunicorn

The Gunicorn WSGI HTTP server is used to serve your application in the case that it is installed. It can be installed by listing it either in the requirements.txt file or in the install_requires section of the setup.py file.

If a file named wsgi.py is present in your repository, it will be used as the entry point to your application. This can be overridden with the environment variable APP_MODULE. This file is present in Django projects by default.

If you have both Django and Gunicorn in your requirements, your Django project will automatically be served using Gunicorn.

• Django development server

If you have Django in your requirements but don't have Gunicorn, then your application will be served using Django's development web server. However, this is not recommended for production environments.

• Python script

This would be used where you provide a Python code file for running you application. It will be used in the case where you specify a path to a Python script via the APP_FILE environment variable, defaulting to a file named app.py if it exists. The script is passed to a regular Python interpreter to launch your application.

• Application script file

This is the most general way of executing your application. It will be used in the case where you specify a path to an executable script file via the APP_SCRIPT environment variable, defaulting to a file named app.sh if it exists. The script is executed directly to launch your application.

Hot deploy

If you are using Django, hot deploy will work out of the box.

To enable hot deploy while using Gunicorn, make sure you have a Gunicorn configuration file inside your repository with the reload option set to true. Make sure to specify your config via the APP_CONFIG environment variable.

To change your source code in running container, use Docker's exec command:

docker exec -it <CONTAINER_ID> /bin/bash

After you enter into the running container, your current directory is set to /opt/app-root/src, where the source code is located.