Ansible-bender in OKD


For the past couple of months, I’ve been working on a project we call “Ansible OCI image builder”. I named the tool itself ansible-bender (and yes, it’s shiny).

Current status

I’m using it almost for 2 months now. There are some bumps here and there but overall it feels pretty solid. The best thing is that I can write Ansible to define my container images.

Therefore I decided it’s time to move to the next stage – orchestrating builds in your cluster. This means that I started integrating ansible-bender into openshift. I chose to take the easy path by utilizing customStrategy type for the builds.

The main problem I ran into was that buildah did not work smoothly in an openshift pod. I was constantly battling some (linux, capabilities, namespaces, kernel) limitations. Here is a list of the most serious issues I encoutered:

  • I was forced to use vfs graph backend because overlay filesystem does not work on top of overlay.
  • Rootless is busted as well — the pod needs to have certain capabilities which openshift drops by default. Therefore the pod is a privileged container.
  • I ran into this buildah issue which stopped my progress completely.
  • And finally, since I still haven’t figured out a definition for metadata of images (you need to pass opts to ansible-bender build now), it’s not possible to set them.

Luckily enough, if you check master branch of origin you’ll be able to see a bunch of commits related to buildah. The most interesting part is that the storage of images is a volume so you are able to use overlay as a backend. Overlay is much faster and efficient than vfs. Since I decided to integrate ab using the custom builds I’m not able to tinker with the configuration of pods. Probably a time to get some feedback from the openshift devs.

Next steps

Since buildah#1251 blocks me, I need that one to be resolved as soon as possible so that I can keep on moving. Once we have some successful builds we can start working on improving the workflow and performance. One of the craziest ideas of mine is to make the Ansible OCI image builder a dedicated build strategy. That would be a lot of work, though.

I’m also planning to show ansible-bender at My Talk is scheduled for Friday, January 25th, 2019, around noon. Please stop by if you want to hear more about building container images using ansible.

This is my update, let’s celebrate New Year’s Eve now.

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