GitLab spot runners & Puppet

We are on AWS with GitLab. For ease of use, and because our build hosts degenerate for some reason (network issues), we decided to use spot instances with GitLab.

The journey was all but easy. Here’s why.

GitLab Runner configuration complaints

First: The process

To configure GitLab runner, you have to …

  • install GitLab,
  • write down the runner registration token,
  • start a runner,
  • manually a registration command using above token.

That registration command will then modify the config file of the runner. That is important because you can’t just write a static, read-only config file and start the runner. This is not possible for two reasons:

  • when you execute the registration command, the runner wants to modify the config file to add yet another token (its “personal” token, not the general registration secret), so it must not be read-only
  • the runner has to be registered, so just starting it will do … nothing.

That is in my eyes a huge design flaw, which undoubtedly has its reasons, but it still – sorry – sucks IMHO.

Second: The configuration

You can configure pretty much everything in the config file. But once the runner registers, the registration process for some reason appends a completely new config to any existing config file, so that … the state is weird. It works, but it looks fucked, and feels fucked.

You can also set all configuration file entries using the gitlab-runner register  command. Well, not all: The global parameters (like, for example, log_level  or concurrent ) cannot be set. Those have to be in a pre-existing config file, so you need both – the file and the registration command, which will look super ugly in a very short time.

Especially if you still use Puppet to manage the runners, cause then you just can’t just restart the runner once the config file changes. Because it will always change, because of above reasons.

Third: The AWS permission documentation

Another thing is that the list of AWS permissions the runner needs in order to create spot instances is nowhere to be found. Hint: EC2FullAccess  and S3FullAccess is not enough. We are using admin permissions right now, until we figured it out. Not nice.

Our solution

For this we’re still using Puppet (our K8S migration is still ongoing), and our solution so far looks like this:

  • Create a config file with puppet next to the designated config file location,
    • containing only global parameters.
    • The file has a puppet hook which triggers an exec that deletes the “final” config file if the puppet-created one has changed.
  • Start the GitLab runner.
  • Perform a “docker exec” which registers the runner in GitLab.
    • The “unless” contains a check that skips execution if the final config file is present.
    • The register  command sets all configuration values except the global ones. Like said above, the command appends all non-global config settings to any existing config file.

Some code

Does this look ugly? You bet.

Should this be a puppet module? Most probably.

Did I foresee this? Nope.

Am I completely fed up? Yes.

Is this stuff I want to do? No.

Does it work?

Yes (at least … 🙂 )

Remarks

If you wander what all those create::THING  entries are – it’s this:

We have an awful lot of those, cause then we can do a lot of stuff in the config YAMLs and don’t need to go in puppet DSL code.