[QA] impove docker administration

[jnweiger]

WHAT Needs to be Documented?

Customer is running a docker-based installation.
Normal maintenance tasks include

• updating apps,
• access logfiles
• update to the next owncloud version.

WHERE Does This Need To Be Documented (Link)?

admin guide

WHY Should This Change Be Made?

Customers should be advised against doing their own docker build to customize their installation.
We should give them enough documentation, so that sysadmin tasks are possible without writing a custom Dockerfile and running docker build ...

We already recommend to persist /mnt/data as a docker volume or filesystem mount.
Add info about /mnt/data/apps ->

• Customers can unpack new apps-x.y.z.tar.gz there, (including chown .R 33:33 app*)
• After a container restart, we can see the new versions including migration steps in the logs.
• how to receive notification about available app updates. (owncloud market app works only when connected to the network)
  -> github releases, customer portal, maretplace.owncloud.com

Add info about /mnt/data/files/owncloud.log ->

• do logrotate there, see that it keeps growing.
• understand how to control log level via env variables.
• understand what is in this owncloud.log and what is exposed in docker logs

Inspecting things inside the docker container

• docker exec -ti $RUNNING_CONTAINER_NAME bash
• use more instead of less or nano or vi (they are not inside our docker) but can be added e.g. via apt update; apt install nano
• understand what is persisted across restarts, and what is not.

Tips for deploying an updated docker image

• database, configs are "upgraded" when a new docker container is tested. Such upgrades (via migration scripts) are not revertable.
• a rollback to a previous owncloud version requires that all database and configs are properly snapshotted before any update attempts!

(Optional) What Type Of Content Change Is This?

• New Content Addition
• Old Content Deprecation
• Existing Content Simplification
• Bug Fix to Existing Content

(Optional) Which Manual Does This Relate To?

• Admin Manual
• Developer Manual
• User Manual
• Android
• iOS
• Branded Clients
• Desktop Client
• Other