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• Separate installation from configuration:  installation should occur in your Dockerfile, dynamic configuration should happen during container startup. 
• Use official images where possible
• Always pin version numbers (avoid "latest")
• Run dependent services in separate containers. If your service requires MySQL, configure it as a dependency, don't install it in your image. 

See also:

• Best practices for writing Dockerfiles
• Guidelines for Official Docker ImagesAlways use the VOLUME instruction to specify the location of mutable data.  For example, Postgres data directory.

Docker best practices

• Containers are ephemeral: they can be stopped and destroyed and a new one built with absolute minimum setup and configuration.
• One process per container
• Minimize layers
• Sort multi-line arguments and split RUN statements for readability
• Use official images as basis for images (Docker recommends Debian because it's small and kept up-to-date)
• Pin versions to avoid failures. Always pin the version of the main application, if installing via apt-get or similar.
• Use CMD or ENTRYPOINT for service-based images. 
  • ENTRYPOINT should be used when you want the container to behave exclusively as if it were the executable it's wrapping. 
  • CMD should be used if the user needs flexibility to run any executable they choose when starting the container.
  • You can combine ENTRYPOINT and CMD to specify a default executable with default arguments that can be overridden
  • Understand shell vs exec uses of CMD.  Prefer exec form for signal handling.
  • If image requires initialization, use ENTRYPOINT and CMD
  • Make sure "bash" works too
  • Model entrypoint.sh use after Postgres
• Use EXPOSE for ports
• Use VOLUME for mutable/customizable parts of image
• Use WORKDIR for clarity
• Use https where possible, import PGP keys with full fingerprint to check package signing, embed checksums in Dockerfile if PGP signing not available
• Forked/detached processes: Containers will stop when the process specified in the "docker run" command stops. For services that generally run detached (e.g., httpd, nginx, postgres), the Dockerfile should call a command that runs in the foreground. For example, the Apache httpd has a "-DFOREGROUND" option.

Dependencies

Often our applications depend on other services.  A particular web application might consist of a web server, application server, database, and search engine. Dependencies introduce complexity when running containers. For example:

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• Dependencies: as discussed above, environment variables providing the IP and PORT of all services in a stack are injected into all related containers.
• System variables: provided for convenience in all containers
• Custom variables

System variables

Custom variables

Labs Workbench supports custom configuration through the use of environment variables. 

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