Salt Container-Map

SaltStack includes the dockerio module for common actions on Docker containers. As an advantage to manual or script-based approaches, this allows for a consistent configuration management. This package includes custom state and execution modules named container_map, complementing the built-in module with the following functionality:

  • Container configurations (e.g. volumes, links, commands) can be managed in pillars, while the actions are created in state files.
  • Dependencies between services are implicitly defined through links and shared volumes. Therefore, they are followed automatically during creation, start, stop, and removal of containers and do not have to be modelled explicitly via require or require_in.
  • Additional volumes can be created automatically to isolate shared resources.
  • When images are updated on the Docker host, it is usually for the purpose of updating the containers depending on that image. This action can be triggered via watch in the dockerio module. With the container_map.update state, the re-creation and restart takes places automatically, also considering dependencies.
  • Changes in volumes, network parameters, and the command or entrypoint parameter also trigger a container re-creation when using container_map.update.
  • In case paths in the virtual filesystem of shared volumes between containers become inconsistent, e.g. due to manual actions or broken containers during a restart of the host system, containers are also re-created as far as necessary.

Along with the state and execution modules comes a custom renderer lazy_yaml. It builds on Salt’s built-in YAML renderer, but adds two custom tags: !pillar and !grain. The !pillar tag is to help the fact that usually pillar files cannot include other pillar items. Instead of being processed by the template renderer, variables are resolved to their actual values just before container_map uses them.

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