Split unit files up into chained steps

[lukebond]

I picked up this tip from the Giantswarm guys.

Currently our unit files do docker pull, docker kill, docker run, docker stop etc. all in messy multi-line bash statements in one unit file. If we separate these into separate unit files, eg. one for pulling, one for starting, one for stopping, etc., and chain them together with systemd requires/after directives then it makes neater unit files as well as making it easier to insert steps in between, such as mounting an EBS volume, starting/connecting to a weave network, etc. It will also unroll on stop/kill and allow you to disconnect these things in reverse order.

[rimusz]

cool, it looks as a nice tip 👍

[tomgco]

@lukebond Sounds good, do you have any examples lying around?

[lukebond]

This is described well by Timo at 13:49 here: https://www.youtube.com/watch?v=OeVMu-1Au78