# FastAPI containerizer (step 4)

This tool **adds container files to an existing completed FastAPI repository**; it never scaffolds or replaces the application. It preserves all four input objects and emits `container_artifacts`, including exact file content and SHA-256 digests.

## Preconditions

The service must contain the configured import module (default `app.main:app`) and a `requirements.lock` containing the complete dependency closure as exact `name==version` pins. The image installs that closure with `--no-deps`, preventing undeclared dependency resolution. If `health_endpoint` is configured, generation fails unless that route literal occurs in Python source; otherwise no health check is emitted.

## Run

```sh
python -m pip install -e .
containerize-fastapi --input prior-step.json --service-dir /path/to/existing/service \
  --output step-4.json --verify-docker
```

Without `--verify-docker`, output explicitly records that Docker was not executed. With it, `container_artifacts.docker_verification` records build/up/down commands, exit codes, bounded logs, and probe status.

Generated files and key lines:

* `Dockerfile`: `FROM python:3.12.8-slim-bookworm`, `pip ... --no-deps -r requirements.lock`, `USER 10001:10001`, and exec-form `python -m uvicorn app.main:app ...`.
* `.dockerignore`: excludes VCS, virtualenvs, caches, secrets, tests, docs, and container files from context.
* `compose.yaml`: one `api` service, local build context, port mapping, read-only root, `/tmp` tmpfs, init, no-new-privileges, and no external services. Health check is conditional.

## Verification

```sh
python -m unittest discover -s tests -v
# Requires a running Docker engine and performs a real build/start/HTTP probe/stop:
./scripts/integration.sh
```

The integration script creates only a disposable fixture to verify this transformation tool. In normal use, artifacts are written directly into the supplied completed service repository.