Start building `system` images with `bake`

[gbartolini]

Issue

The official Docker image for Postgres project has removed support for Debian 11 (bullseye) in favour of Debian 13 (trixie). See: PR #1354. However, “bullseye” is maintained for another year (31 August 2025).

The removal of “bullseye” from the official Docker images of Postgres creates an unexpected and unprecedented (though probably foreseeable) problem with the default CloudNativePG Postgres container images: although we have prepared the ground for the new set of images, called “minimal” and “standard”, and built through “bake” directly from Debian base images, the default images are still based on the “bullseye” official Docker images.

For example, a typical “cluster-example.yaml” deployment will ship “ghcr.io/cloudnative-pg/postgresql:17.5” which, due to the default rolling tag policy, maps to “bullseye”:

$ kubectl exec -ti cluster-example-1 -c postgres -- cat /etc/os-release
PRETTY_NAME="Debian GNU/Linux 11 (bullseye)"
NAME="Debian GNU/Linux"
VERSION_ID="11"
VERSION="11 (bullseye)"
VERSION_CODENAME=bullseye
ID=debian
HOME_URL="https://www.debian.org/"
SUPPORT_URL="https://www.debian.org/support"
BUG_REPORT_URL="https://bugs.debian.org/"

In January 2025, we did not change the default images because we planned to phase them out with CloudNativePG 1.28 and the deprecation of Barman Cloud (the only reason those images still exist), avoiding our users a double notification of change. See this comment for details.

Proposed solution

Add the system flavour to the new bake process by basing the system image on the standard one and adding Barman Cloud to it.

Partially solves #277.

IMPORTANT: Before closing this ticket, open a new ticket in cloudnative-pg to make 17.6-system-trixie the new default image.