# Endpoint Monitor

A typed FastAPI service that stores endpoint monitors in process-local memory and performs secure, on-demand HTTP checks.

## Quick start

Requires Python 3.12.

```sh
python -m venv .venv
. .venv/bin/activate
pip install -e '.[dev]'
make check
uvicorn app.main:app --reload --workers 1
```

Create and check a monitor:

```sh
curl -sS -X POST http://localhost:8000/v1/monitors \
  -H 'content-type: application/json' \
  -d '{"name":"example","url":"https://example.com/health?token=do-not-log"}'
curl -sS -X POST http://localhost:8000/v1/monitors/MONITOR_UUID/checks
curl -sS http://localhost:8000/v1/monitors/MONITOR_UUID/status
```

Interactive OpenAPI documentation is at `/docs`. The full route/status/error contract and SSRF model are in [docs/service-design.md](docs/service-design.md).

## Configuration

All values are startup-validated and use environment prefix `MONITOR_`:

| Variable | Default | Constraint |
|---|---:|---|
| `MONITOR_APP_NAME` | endpoint-monitor | string |
| `MONITOR_LOG_LEVEL` | INFO | logging level |
| `MONITOR_CHECK_TIMEOUT_SECONDS` | 5 | >0, <=30 |
| `MONITOR_MAX_REDIRECTS` | 5 | 0–10 |
| `MONITOR_MAX_RESPONSE_BYTES` | 1000000 | 1–10000000 |

Checks resolve every hop and block any hostname with a non-public answer. Redirects are manual and bounded; total elapsed timeout and response size are bounded. Query and fragment data and URL credentials are redacted from structured logs. URL credentials are rejected. Application checks cannot create a perfect DNS-rebinding boundary; use deny-by-default egress networking or a hardened outbound proxy in sensitive deployments.

## Tests and quality

```sh
make lint       # Ruff formatting check and lint
make type       # strict mypy
make test       # pytest API/unit suite
make check      # all three
```

Tests are directly inspectable under `tests/`: CRUD/operations and API mapping (`test_api.py`), lock concurrency and stale compare-and-set updates (`test_store.py`), timeouts/statuses/DNS and redirect SSRF/log redaction (`test_checker.py`), and environment validation (`test_config.py`). Outbound requests use `httpx.MockTransport`; tests do not access the network.

## Container

```sh
docker build -t endpoint-monitor:local .
docker run --rm -p 8000:8000 endpoint-monitor:local
# or
docker compose up --build
```

The image runs as a non-root user, has a liveness healthcheck, and deliberately starts one Uvicorn worker.

## Layout

```text
app/                    service implementation
  checker.py            bounded checks, DNS/redirect SSRF policy
  config.py             validated environment settings
  logging.py            structured JSON and URL redaction
  main.py               FastAPI routes and lifecycle
  models.py             API schemas and status semantics
  store.py              lock-protected in-memory state and CAS updates
tests/                  mocked unit and API tests
docs/service-design.md  contract and architecture
docs/verification.md    execution record and reproducible commands
Dockerfile, compose.yaml, pyproject.toml, Makefile
```

## Important limitations

All monitors disappear on restart. State is not shared between processes, hosts, or Uvicorn workers, so run exactly one worker. There is no authentication; place the service behind an authenticated gateway if exposed. For durable or horizontally scaled use, replace `MonitorStore` with a transactional shared datastore and coordinate check ownership.