Debian 11 (bullseye) backports repository is deprecated but still included in sources.list template

[challvy]

Description

The Debian 11 (bullseye) backports repository has been deprecated, but cloud-init continues to generate it in /etc/apt/sources.list when provisioning Debian 11 systems. This causes APT warnings and potential package installation issues.

• https://backports.debian.org/Instructions/

For example, Debian 12 'bookworm' was released on June 10th 2023, so bullseye-backports for Debian 11 'bullseye' was closed on June 10th 2024.

• https://lists.debian.org/debian-backports-announce/2024/07/msg00000.html

Steps to Reproduce

1. Deploy a Debian 11 (bullseye) instance using cloud-init
2. Check /etc/apt/sources.list
3. Observe that bullseye-backports repository is included

Current Behavior

The template /etc/cloud/templates/sources.list.debian.tmpl generates backports repository for all Debian versions including bullseye:

deb http://deb.debian.org/debian bullseye-backports main
deb-src http://deb.debian.org/debian bullseye-backports main

Expected Behavior

Debian 11 (bullseye) and later versions should NOT include the backports repository since it has been deprecated by the Debian project.

Proposed Fix

Modify templates/sources.list.debian.tmpl to conditionally exclude backports for Debian 11 (bullseye):

{% if codename != 'bullseye' %}deb {{mirror}} {{codename}}-backports main
{% endif %}{% if codename != 'bullseye' %}deb-src {{mirror}} {{codename}}-backports main
{% endif %}

Impact

• Affected versions: Debian 11 (bullseye)
• Unaffected versions: Debian 10 (buster) and earlier, Debian 12 (bookworm) and later
• Severity: Medium - causes APT warnings and repository errors

Additional Context

• Debian 11 backports repository was officially deprecated
• Users experience APT errors: The repository 'http://deb.debian.org/debian bullseye-backports Release' does not have a Release file
• This affects all cloud-init deployments on Debian 11 that use the default apt configuration

Environment

• cloud-init version: 25.1.3
• Distribution: Debian 11 (bullseye)
• Template file: templates/sources.list.debian.tmpl