# OTel LGTM (Alpine + supervisord)

A single-container observability backend running on Alpine Linux with supervisord.

Components:

- **Grafana** — visualization UI
- **Mimir** — metrics storage
- **Loki** — log storage
- **Tempo** — trace storage
- **OpenTelemetry Collector (contrib)** — OTLP receiver and router

## Ports

| Port | Service | Description |
|------|---------|-------------|
| 3000 | Grafana | Web UI |
| 4318 | OTel Collector | OTLP/HTTP endpoint |

Only these two ports are exposed. All other services communicate internally on `127.0.0.1`.

## Build

```bash
docker build -t otel-lgtm .
```

> The Dockerfile uses BuildKit cache mounts for `apk`. Make sure BuildKit is enabled (default in recent Docker Desktop / `docker buildx`).

### Build args

| Build arg | Default | Description |
|-----------|---------|-------------|
| `ALPINE_VERSION` | `3.24` | Alpine Linux base image version |
| `OTELCOL_VERSION` | `0.154.0` | OpenTelemetry Collector Contrib version |

Grafana, Mimir, Loki, and Tempo versions are determined by the chosen Alpine repository.

Example:

```bash
docker build --build-arg OTELCOL_VERSION=0.155.0 -t otel-lgtm .
```

### Multi-architecture

The Dockerfile detects the build architecture at build time, so it works on both `amd64` and `arm64`. To build a true multi-arch image in one command, use Docker BuildKit / `docker buildx`:

```bash
docker buildx build --platform linux/amd64,linux/arm64 -t otel-lgtm .
```

## Run

```bash
docker run -p 3000:3000 -p 4318:4318 -v lgtm-data:/data otel-lgtm
```

Grafana is available at http://localhost:3000 with anonymous admin access enabled.

Send telemetry to the collector at `http://localhost:4318` (OTLP/HTTP).

## Data persistence

All persistent data is written under `/data`:

| Path | Service |
|------|---------|
| `/data/grafana` | Grafana data, logs, and plugins |
| `/data/mimir` | Mimir metrics storage |
| `/data/loki` | Loki log storage |
| `/data/tempo` | Tempo trace storage |

Mount a volume there to persist data across container restarts.

## Architecture

```
Application ──OTLP/HTTP──> OTel Collector :4318
    │
    ├─ metrics ──OTLP/HTTP──> Mimir :9009
    ├─ logs ─────OTLP/HTTP──> Loki :3100
    └─ traces ───OTLP/HTTP──> Tempo :3200

Grafana :3000 queries Mimir, Loki, and Tempo.
```

## Read-only root filesystem

The image can be run with an immutable root filesystem (`--read-only`). A few runtime-only directories must be mounted as writable `tmpfs`:

```bash
docker run --read-only \
  -p 3000:3000 -p 4318:4318 \
  -v lgtm-data:/data \
  --tmpfs /tmp:rw,noexec,nosuid,size=100m \
  --tmpfs /run:rw,noexec,nosuid,size=10m \
  --tmpfs /var/log/supervisor:rw,noexec,nosuid,size=50m \
  otel-lgtm
```

Persistent data continues to live on the `/data` volume, while temporary/runtime state stays in memory.

## Notes

- This image is intended for development, demo, and testing environments.
- Grafana authentication is disabled (`anonymous` admin).
- Grafana’s default async plugin pre-installation is disabled to avoid relying on internet access at startup.