Cloud-init installing packages on Debian with contrib sources

Question

I need to install some zfs packages on Debian instances using cloud-init. One of the packages needs the contrib sources. I can get it to update the sources list, but the packages fail to install. If I remove the contrib source lists, some packages install, just not the ones that need contrib. Kind of a catch 22. Has anyone had success installing zfs and all prerequisites using cloud-init?

Here is what I am using, when I add package_update or preserve_sources_list: true it fails to update the sources.list file. I can't win. lol Thanks!

#cloud-config
locale: en_US.UTF-8
timezone: America/New_York
apt:
  sources_list: | # needed for spl package
    deb $MIRROR $RELEASE bullseye main contrib
    deb-src $MIRROR $RELEASE bullseye main contrib
    deb $MIRROR $RELEASE bullseye-updates main contrib
    deb-src $MIRROR $RELEASE bullseye-updates main contrib
    deb $MIRROR $RELEASE bullseye-security main contrib
    deb-src $MIRROR $RELEASE bullseye-security main contrib
packages:
  - linux-headers-5.10.0-21-amd64
  - linux-image-amd64
  - spl
  - kmod
  - snapd
  - nfs-common
  - htop
  - nano
  - build-essential
  - zfsutils-linux
  - zfs-dkms
  - zfs-zed
runcmd:
  - mkdir /mnt/v-nas
  - mkdir /mnt/home

Answer 1

Your source lines look wrong. On debian bullsye, $RELEASE will be replaced with bullseye.

Therefore this:

deb $MIRROR $RELEASE bullseye main contrib

Should get rendered into your apt list config as:

deb http://some.site.com/ bullseye bullseye main contrib

Is that really supposed to have two bullseye entries?