# Architecture

This project runs Traefik Proxy as a Dockerized TCP load balancer.

## Components

- `compose.yaml`: defines the Traefik container, host networking, host-based configuration volume, container hardening, and healthcheck.
- `config/traefik.yml`: static Traefik configuration for HTTP, TCP TLS, ping, file provider, and logging.
- `config/dynamic/*.yml`: dynamic per-site HTTP routers, TCP routers, and backend load-balancer services.

## Data flow

1. A client opens a TLS connection to the Docker host on `443/tcp`.
2. Traefik receives the connection directly through host networking on `443/tcp`.
3. Traefik matches the TCP router using `HostSNI(...)`.
4. Traefik forwards the unchanged TCP stream to one configured backend IP address and port.
5. The selected backend terminates TLS and presents its own SSL certificate.

For HTTP-01 certificate validation:

1. Let's Encrypt opens an HTTP connection to the Docker host on `80/tcp`.
2. Traefik receives the request directly through host networking on `80/tcp`.
3. Traefik matches the HTTP `Host(...)` router.
4. Traefik forwards the full HTTP request to the configured local backend so that backend redirects and ACME challenge handling remain in one place.

## Persistence

Traefik configuration is stored in the host `./config` directory and mounted read-only at `/etc/traefik`.

No certificates, private keys, application data, or Docker socket are mounted into the Traefik container.

## Deployment topology

Traefik runs as one Docker container on the load-balancer host with `network_mode: host`. Backends are external to this Compose stack and can be reached on host loopback addresses such as `127.0.0.1:8443`.

See `docs/adr/0001-traefik-tcp-tls-passthrough.md` for the design decision.