Docker init Systems

There are a number of init systems used on docker containers, many are the defaults that ship with the standard Linux distributions, e.g. systemd which is particularly popular on the larger comprehensive distributions.

When creating my own imaged I have generally is the S6-RC init system, most if not all have been built on the latest Apline Linux as base image. Some examples:

• DNS (ISC Bind9)
• DHCP server (ISC Kea)
• Torrent server (Deluge)
• mailserver (yes, while I have got this to operate it needs some/a lot of cleanup and consolidation, including the main wiki documenation)
  • Mail server (Postfix and Dovecot)
  • Mail server database and web interface (mariadb php nginx)
  • Web Mailserver (Roundcube, postgresdb)

I have also used supervisord system where it was simple to follow the formula from the image supplier to add functionality. Some examples:

• Nextcloud (only example)

There are other init systems out there that I have not looked into, including a number of legacy init systems that are no longer supported.

I decided to build this container image based upon Alpine Linux using the S6 init system. The Skarnet.org is the S6 authors web site and main repository. S6 seems to be one of the most performant small init systems available, however it is not very easy to use. I could really use a front-end to help with the management.

S6 Service directories

Basic S6 commands:

Reference:

• just-containers/s6-overlay (Version 3.1.6.2 as of 2023-11-21, last checked 2024-04-28)
• The s6-rc-compile program Describes the functionality of the S6-rc system
• Easy to follow Beginner Guide on s6 Starter Pack

Other Supervisor software discussions:

• Choosing an init process for multi-process containers - Interesting discussion on different init systems, current at that time. (Seems relevant now too.)
• supervisord: Supervisor: A Process Control System
• Use of Supervisor in docker