# ADR 0001 — Base Image Selection

**Status:** Accepted

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## Context

The runner needs a base OS image that provides:
- A working apt package ecosystem for installing `git`, `curl`, `jq`, `tini`, `ca-certificates`, `tzdata`.
- Compatibility with Docker's official apt repository (for Docker CLI).
- Compatibility with NodeSource (for Node.js 20 LTS).
- A label environment the existing workflows reference: `ubuntu-latest`.

Candidates considered:
1. `ubuntu:22.04` — LTS, wide ecosystem support, good compatibility.
2. `ubuntu:24.04` — Newer LTS, some tooling still stabilizing.
3. `debian:bookworm-slim` — Smaller footprint, good compatibility, but `ubuntu-latest` label mismatch.
4. `debian:bullseye-slim` — Older, stable, but further from `ubuntu-latest` expectations.

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## Decision

Use `ubuntu:22.04` as the base image, pinned by exact tag.

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## Rationale

- Existing Gitea workflows use `runs-on: ubuntu-latest`. Basing the runner image on Ubuntu 22.04 maximizes compatibility with GitHub Actions steps written for that environment.
- Ubuntu 22.04 LTS has long-term support through 2027, reducing forced base image churn.
- Docker's apt repository and NodeSource both officially support Ubuntu 22.04.
- Ubuntu 22.04 is the most common self-hosted runner base image in community examples, so troubleshooting resources are abundant.

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## Consequences

- Final image size will be larger than a minimal Alpine or Debian slim base, which is acceptable given the goal of bundling all runtime dependencies.
- When the workflow ecosystem moves to `ubuntu-24.04`, the base image can be bumped with a version argument change (`ARG UBUNTU_VERSION=24.04`).

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## Alternatives considered

**Debian bookworm-slim:** Smaller image, but the `ubuntu-latest` label in existing workflows creates an expectation of Ubuntu compatibility. Switching to Debian may cause subtle incompatibilities with actions that check the OS ID.

**Ubuntu 24.04:** Not yet the default for `ubuntu-latest` as of the initial build date; 22.04 remains the more tested choice for self-hosted runners.