.. index::
   pair: Docker ; Best practices
   ! Docker Best practices


.. _docker_best_practices_nick:

=============================================
Docker Best practices from Nick Janetakis
=============================================

.. seealso::

   - :ref:`nick_janetakis`
   - https://nickjanetakis.com/blog/best-practices-when-it-comes-to-writing-docker-related-files
   - https://github.com/nickjj/docker-web-framework-examples
   - https://dev.to/nickjj/best-practices-when-it-comes-to-writing-docker-related-files-ek3
   - https://github.com/nickjj/docker-web-framework-examples


.. contents::
   :depth: 3


Dockerfile
===========

- Use Alpine as a base image unless you can’t due to technical reasons
- Pin versions to at least the minor version, example: 2.5-alpine not 2-alpine
- Add a maintainer LABEL to keep tabs on who initially made the image
- Only include ARG and ENV instructions if you really need them
- Use /app to store your app’s code and set it as the WORKDIR (if it makes sense)
- When installing packages, take advantage of Docker’s layer caching
  techniques
- If your app is a web service, *EXPOSE 8000 unless you have a strong
  reason not to*
- Include a wget driven HEALTHCHECK (if it makes sense)
- Stick to the [] syntax when supplying your CMD instructions


docker-compose.yml
=====================

- List your services in the order you expect them to start
- Alphabetize each service’s properties
- Double quote all strings and use {} for empty hashes / dictionaries
- Pin versions to at least the minor version, example: 10.4-alpine
  not 10-alpine
- Use . instead of $PWD for when you need the current directory’s path
- Prefer build: "." unless you need to use args or some other sub-property
- If your service is a web service, publish port 8000 unless it doesn’t
  make sense to


.dockerignore
=================

- Don't forget to create this file :D
- Don't forget to add the .git folder
- Don't forget to add any sensitive files such as .env.production


Example Apps for Popular Web Frameworks
=========================================


I've put together a few example applications that stick to these best
practices.

You can find them all on https://github.com/nickjj/docker-web-framework-examples
Fully working Docker Compose based examples that you can reference:

- Flask
- Node / Express
- Phoenix
- Rails
- Webpack

If you don't see your favorite web framework listed above, open up a PR!
This repo is meant to be a community effort where we can work together
to make high quality example apps that demonstrate Dockerizing popular
web frameworks and libraries.



Flask example
==============

.. seealso::

   - https://github.com/nickjj/docker-web-framework-examples/tree/master/flask

Flask Dockerfile
------------------


::

    FROM python:2.7-alpine
    LABEL maintainer="Nick Janetakis <nick.janetakis@gmail.com>"

    # If you plan to use PostgreSQL then you must add this package: postgresql-dev.
    RUN apk update && apk add build-base

    WORKDIR /app

    COPY requirements.txt requirements.txt
    RUN pip install -r requirements.txt

    COPY . .

    EXPOSE 8000
    HEALTHCHECK CMD wget -q -O /dev/null http://localhost:8000/healthy || exit 1

    CMD ["gunicorn", "-c", "python:config.gunicorn", "hello.app:create_app()"]


.env file
-----------

::

    COMPOSE_PROJECT_NAME=flaskhello
    PYTHONUNBUFFERED=true

Flask docker-compose.yml
---------------------------


.. code-block:: yaml

    version: "3.6"

    services:
      web:
        build: "."
        command: >
          gunicorn --reload -c "python:config.gunicorn" "hello.app:create_app()"
        env_file:
          - ".env"
        ports:
          - "8000:8000"
        volumes:
          - ".:/app"



hello/app.py
--------------

::

    from flask import Flask
    from werkzeug.debug import DebuggedApplication


    def create_app(settings_override=None):
        """
        Create a Flask application using the app factory pattern.

        :param settings_override: Override settings
        :return: Flask app
        """
        app = Flask(__name__, instance_relative_config=True)

        app.config.from_object('config.settings')
        app.config.from_pyfile('settings.py', silent=True)

        if settings_override:
            app.config.update(settings_override)

        if app.debug:
            app.wsgi_app = DebuggedApplication(app.wsgi_app, evalex=True)

        @app.route('/')
        def index():
            return 'Hello world with DEBUG={0}'.format(app.config['DEBUG'])

        @app.route('/healthy')
        def healthy():
            return ''

        return app



.gitignore
-----------

.. seealso::

   - https://www.gitignore.io/api


::

    # Created by https://www.gitignore.io/api/python,osx

    ### OSX ###
    *.DS_Store
    .AppleDouble
    .LSOverride

    # Icon must end with two \r
    Icon

    # Thumbnails
    ._*

    # Files that might appear in the root of a volume
    .DocumentRevisions-V100
    .fseventsd
    .Spotlight-V100
    .TemporaryItems
    .Trashes
    .VolumeIcon.icns
    .com.apple.timemachine.donotpresent

    # Directories potentially created on remote AFP share
    .AppleDB
    .AppleDesktop
    Network Trash Folder
    Temporary Items
    .apdisk

    ### Python ###
    # Byte-compiled / optimized / DLL files
    __pycache__/
    *.py[cod]
    *$py.class

    # C extensions
    *.so

    # Distribution / packaging
    .Python
    build/
    develop-eggs/
    dist/
    downloads/
    eggs/
    .eggs/
    lib/
    lib64/
    parts/
    sdist/
    var/
    wheels/
    *.egg-info/
    .installed.cfg
    *.egg

    # PyInstaller
    #  Usually these files are written by a python script from a template
    #  before PyInstaller builds the exe, so as to inject date/other infos into it.
    *.manifest
    *.spec

    # Installer logs
    pip-log.txt
    pip-delete-this-directory.txt

    # Unit test / coverage reports
    htmlcov/
    .tox/
    .coverage
    .coverage.*
    .cache
    .pytest_cache/
    nosetests.xml
    coverage.xml
    *.cover
    .hypothesis/

    # Translations
    *.mo
    *.pot

    # Flask stuff:
    instance/settings.py
    .webassets-cache

    # Scrapy stuff:
    .scrapy

    # celery beat schedule file
    celerybeat-schedule.*

    # End of https://www.gitignore.io/api/python,osx