# spark-mcp-go

MCP (Model Context Protocol) server for Apache Spark on YARN. Lets an LLM agent
discover Spark/YARN endpoints, submit jobs, fetch logs, and analyze them via
11 typed Tools. Streamable HTTP transport, SQLite-backed configuration, and
`log/slog` structured logging with per-Tool call files.

## What it does

- Exposes 11 MCP Tools over Streamable HTTP at `/mcp`
- Admin API at `/admin/*` for cluster and audit configuration
- HTTP Basic and YARN SimpleAuth for Spark/YARN endpoints
- SSRF protection with cluster URL allowlist plus DNS rebinding guard
- Per-Tool independent audit log (file mode `0600`)
- `spark-submit` via local `exec.Command` (no shell, no injection)

## Quick start (3 steps)

1. Copy and edit the environment file:
   ```bash
   cp .env.example .env
   # Edit ADMIN_TOKENS and AGENT_TOKEN
   ```

2. Build and start the server:
   ```bash
   go build ./...
   ./spark-mcp-go
   # Or use the helper:
   # ./scripts/dev.sh
   ```

3. Initialize an MCP session, then call `list_clusters` to discover endpoints.

## 11 Tools

| Tool | Type | Purpose |
|---|---|---|
| `list_clusters` | discovery | Return all active clusters (LLM entry point) |
| `spark_submit` | exec | Local `spark-submit` process, extracts `app_id` |
| `list_applications` | RM | `GET /ws/v1/cluster/apps[?state=&user=]` |
| `get_application_status` | RM | `GET /ws/v1/cluster/apps/{id}` |
| `get_application_logs` | RM | Fallback chain: `amContainerLogs` -> aggregated-logs -> logs |
| `kill_application` | RM | `PUT` state `KILLED` |
| `fetch_spark_metrics` | SHS | Executor metrics + summary mode triggers analyzer |
| `fetch_cluster_env` | RM | Aggregate `/cluster/info` and `/cluster/metrics` |
| `analyze_spark_log` | analyzer | RM logs + heuristic rules + LLM-ready prompt |
| `fetch_url` | HTTP | Generic primitive, uses cluster allowlist and auth |
| `upload_file` | FS | Write to `./data/uploads/`, reference from `spark_submit` |

## Environment variables

| Variable | Default | Required | Description |
|---|---|---|---|
| `LISTEN_ADDR` | `:8080` | no | HTTP listen address |
| `DATA_DIR` | `./data` | no | SQLite, uploads, and log root |
| `ADMIN_TOKENS` | — | **yes** | Comma-separated tokens for `/admin/*` |
| `AGENT_TOKEN` | — | **yes** | Token for `/mcp` requests |
| `HTTP_CLIENT_TIMEOUT` | `30s` | no | Timeout for `fetch_url`/RM Tool HTTP calls |
| `MAX_RESPONSE_BYTES` | `1048576` (1 MiB) | no | HTTP response truncation limit |
| `SPARK_SUBMIT_TIMEOUT` | `60s` | no | `spark-submit` process timeout |
| `LOG_DIR` | `./data/logs` | no | Log root directory |
| `LOG_LEVEL` | `info` | no | `debug`, `info`, `warn`, or `error` |
| `LOG_FORMAT` | `text` | no | `text` for terminal, `json` for log files |
| `ANALYZER_DATA_SKEW_RATIO` | `3.0` | no | Data-skew rule threshold (max/min ratio) |
| `ANALYZER_GC_PRESSURE_RATIO` | `0.1` | no | GC-pressure rule threshold (GC/CPU ratio) |
| `ANALYZER_BOTTLENECK_SHUFFLE_GB` | `50` | no | Bottleneck rule threshold (shuffle GB) |

## Admin API

All endpoints require `Authorization: Bearer <admin_token>`.

| Method | Path | Description |
|---|---|---|
| `GET` | `/admin/clusters` | List all clusters |
| `POST` | `/admin/clusters` | Create a cluster |
| `GET` | `/admin/clusters/:id` | Get one cluster |
| `PUT` | `/admin/clusters/:id` | Update a cluster |
| `DELETE` | `/admin/clusters/:id` | Delete a cluster |
| `GET` | `/admin/audit?limit=100` | Query audit log |

Create a cluster:

```bash
curl -sS -X POST \\
  -H "Authorization: Bearer ${ADMIN_TOKEN}" \\
  -H "Content-Type: application/json" \\
  -d '{
    "id": "prod",
    "name": "prod",
    "rm_url": "http://rm.example.com:8088",
    "shs_url": "http://shs.example.com:18080",
    "spark_submit_execute_bin": "/opt/spark/bin/spark-submit",
    "is_active": true,
    "auth_type": "simple",
    "auth_username": "yarn",
    "rate_limit_per_min": 10,
    "url_allowlist": ["rm.example.com:8088", "shs.example.com:18080"]
  }' \\
  "http://127.0.0.1:${LISTEN_ADDR:-:8080}/admin/clusters"
```

Note: `auth_password` is not accepted via JSON (`json:"-"`). Set it through a
dedicated password endpoint or seed the database directly.

## Security model

Three lines of defense:

1. **Token auth** - `ADMIN_TOKENS` protects `/admin/*`; `AGENT_TOKEN` protects `/mcp`.
2. **SSRF guard** - Every outbound URL must match the cluster's `url_allowlist`,
   with private-IP CIDR blacklist (incl. `169.254.0.0/16` AWS/GCP metadata).
3. **Path allowlist** - `upload_file` writes only to `./data/uploads/`, rejects
   absolute paths, `..`, and non-`[a-zA-Z0-9._-]` filenames.

Additional guarantees:

- `spark_submit` runs the cluster's binary via `exec.Command(name, args...)` —
  slice form, never `sh -c`. No shell metacharacter interpretation.
- `auth_password` is tagged `json:"-"`; never serialized in responses, never
  accepted from JSON request bodies.
- Cross-host redirects (RM → NM 307) preserve the `Authorization` header
  through `DoWithRedirect` only when the destination host is in
  `url_allowlist`.
- Per-Tool log files are created with mode `0600` and live under
  `./data/logs/tools/`.

## Development

```bash
go build ./...
go test ./...
go vet ./...
```

## More docs

- [ARCHITECTURE.md](ARCHITECTURE.md) - Design and package layout
- [docs/runbook.md](docs/runbook.md) - Deployment, upgrade, and troubleshooting