carloss fzzf: We use a nodepool-builder [1] service to build our custom images. Actually, our setup is (almost) identical to OpenDev's [2], i.e., we use the same elements. Nodepool uses the diskimage-builder tool [3] to build custom images, I'd recommend reading its documentation if you haven't already. We are using Software Factory [4] to automatically deploy a Nodepool + Zuul environment.

[1] https://zuul-ci.org/docs/nodepool/latest/operation.html#nodepool-builder
[2] https://opendev.org/openstack/project-config/src/branch/master/nodepool/nodepool.yaml#L298-L304
[3] https://docs.openstack.org/diskimage-builder/latest/
[4] https://softwarefactory-project.io/docs/