Blog: S6 Overlay (#462)

blog/2020-04-12-s6-overlay.md

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+---
+author: Franck Nijhof
+authorURL: https://twitter.com/frenck
+authorImageURL: /img/profile/frenck.png
+authorTwitter: frenck
+title: S6 Overlay for our Docker containers
+---
+
+Home Assistant uses a lot of different Docker containers for all kinds of
+purposes. Not only the Home Assistant Core that is available as Docker
+containers but also our Supervisor and all add-ons are leveraging Docker.
+
+In many situations, we need to run multiple processes in our containers,
+that all need to be managed. We used to do this using simple Bash scripting,
+but quickly learned we need a proper process manager to handle this.
+
+We decided to use the [S6 Overlay init system][s6-overlay], which is based on
+the excellent [S6][s6] toolset that provides process supervision and
+management, logging, and system initialization.
+
+The S6 Overlay has been added to our [Docker base images][base-imags],
+which is used by every Docker image Home Assistant ships.
+
+All containers have been updated, and changes are automatically handled by the
+Home Assistant Supervisor; For Home Assistant users, there is no noticeable
+impact.
+
+For users of the Home Assistant Core containers on Docker, this might impact
+the way you run or start the container. If you run your Home Assistant Core
+container with an override of the Docker entry point or command, you need to
+adapt those. For example, some container management systems, like Portainer
+and Synology, automatically override those for you so you are impacted.
+
+In those cases:
+
+- The entry point has changed to: `/init`
+- The command (CMD) has changed to: ` ` _(Empty/not set)_
+
+If you override the command endpoint to start Home Assistant, the init system
+in the entry point will still be active in the background and a second launch
+Home Assistant. This can lead to unexpected behavior.
+
+[base-imags]: https://github.com/home-assistant/docker-base
+[s6-overlay]: https://github.com/just-containers/s6-overlay
+[s6]: http://skarnet.org/software/s6/