# Dockerfile & build

Every service runs containerized as the shared **`services`** account: **uid/gid
1337**, fixed fleet-wide. Build your image to be **uid-agnostic** so it runs cleanly
as that account.

```dockerfile
FROM python:3.12-slim
ENV HOME=/tmp                                  # services account has no home dir; $HOME must be writable

WORKDIR /app
RUN apt-get update \
    && apt-get install -y --no-install-recommends git \
    && rm -rf /var/lib/apt/lists/*             # include git ONLY if the container itself needs it

COPY requirements.txt .
RUN pip install --no-cache-dir -r requirements.txt   # deps before code — see layer caching

COPY . .
RUN chmod -R a+rwX /app                         # writable by any uid — this is "uid-agnostic"
CMD ["python", "-m", "yourapp"]
```

- **`HOME=/tmp`** — the `services` account has no home dir; anything writing to `$HOME`
  (caches, configs) needs a writable target.
- **`git`** — include it **only if the container itself needs it** (e.g. you
  `pip install` from git, or the app shells out to git). The build and host always have
  git; this is about what's *inside* the image.
- **`chmod -R a+rwX /app`** — makes the app tree writable by any uid, so it runs as
  1337.

## Layer caching

Copy the deps file and install **before** `COPY . .`. Docker caches layers in order, so
deps only reinstall when the deps file changes — not on every code edit. Get this
backwards and every one-line change triggers a full dependency reinstall.

```dockerfile
COPY requirements.txt .                              # pip baseline
RUN pip install --no-cache-dir -r requirements.txt   # cached until deps change
COPY . .                                             # changes every build
```

## Getting your files into the image

`COPY . .` grabs the whole repo, but be explicit about anything that needs its own
place — assets, templates, a config the app reads at runtime. In `COPY <src> <dest>`,
`<src>` is relative to the build context (your repo) and `<dest>` is a path in the
image.

```dockerfile
COPY ./config.toml /app/config.toml   # a single file into a specific path
COPY ./assets /app/assets             # a whole directory (tree mirrors ./assets/)
```

!!! warning "Don't `COPY` secrets into the image"
    Anything sensitive stays **out** of the image — no `COPY ./secrets.env`. Secrets
    live on the host and are injected read-only at runtime (see
    **[Secrets](secrets.md)**). Add them to `.dockerignore` so a blanket `COPY . .`
    can't sweep them in.

## Faster builds with uv (optional)

[uv](https://docs.astral.sh/uv/) is a drop-in for pip that reads the same
`pyproject.toml` — no lockfile needed in the image. Swap the deps layer and add
`UV_COMPILE_BYTECODE` so containers don't pay the first-import `.pyc` compile cost:

```dockerfile
FROM python:3.12-slim
COPY --from=ghcr.io/astral-sh/uv:latest /uv /uvx /bin/   # pull the uv binary from its image
ENV HOME=/tmp
ENV UV_COMPILE_BYTECODE=1                                # compile bytecode at build, not first cold start

WORKDIR /app
COPY pyproject.toml .
RUN uv pip install --system .                            # --system: into the image's Python, no venv/lock
COPY . .
RUN chmod -R a+rwX /app
CMD ["python", "-m", "yourapp"]
```

## Checklist

- `HOME=/tmp`
- `chmod -R a+rwX /app` (uid-agnostic; runs as the `services` account, 1337)
- deps installed **before** the code copy (layer caching) — pip or `uv pip install`
- `git` in the image **if the container needs it**
- using uv? add `ENV UV_COMPILE_BYTECODE=1`

See **[Compose convention](compose.md)** for the `compose.yaml`, and
**[Secrets](secrets.md)** for credentials.