Add ubuntu docker image

[lox]

We still refer to an ubuntu docker image in https://buildkite.com/docs/agent/v3/docker. I think it makes sense to offer an ubuntu variant as well as alpine.

This will have a -ubuntu suffix, so buildkite/agent:3.0-ubuntu and will use the latest LTS.

[toolmantim]

We deprecated the Ubuntu image quite a while ago… we just forgot to update the docs. I wonder if it's a good idea to bring it back? Then we'd add jessie too I guess? We initially deprecated it to reduce the support footprint.

We could instead have some instructions for building your own Ubuntu + Jessie images?

[lox]

It seems like it's pretty standard to have a default alpine build but also an ubuntu or debian build for things @toolmantim. I'm ok with adding it to the build process, enough people have asked and the size of the ubuntu image has come right down over time. Feels?

[toolmantim]

Cool cool, sounds worth it?

The only other thing maybe to consider is keeping our OS base up-to-date with security vulns too? Alpine base tends to have much less vulns, and at the moment we only update our images on agent release at the moment.

https://hub.docker.com/r/buildkite/agent/tags/

[toolmantim]

How do other people handle that I wonder? With Docker Hub auto-build you can have it trigger based on other dependent images. We could use a daily scheduled build? So package updates would be picked up max 24h after the OS packages are updated.

[lox]

Yeah, it's a tricky problem. We basically need to monitor upstream images somehow and trigger agent builds, but we also need a way to notify us so we can cut new releases.

[harrietgrace]

Sweet! @lox, so in the docs, should the command be:

docker run -e BUILDKITE_AGENT_TOKEN="INSERT-YOUR-AGENT-TOKEN-HERE" buildkite/agent:3.0-ubuntu

Does that mean the alpine one should have the buildkite/agent:3.0 bit at the end too, instead of just buildkite/agent?

[lox]

I might make buildkite/agent:ubuntu work @harrietgrace!

[harrietgrace]

That would be rad 🙏🏻 Thanks!

[lox]

The alpine one doesn't have a suffix, so buildkite/agent:3.0, buildkite/agent:3 or buildkite/agent:latest would all refer to the alpine image.