WebRTC Outpost

Configuration repository for a Coturn relay that supports a Stoat deployment on GCP. The stack provisions a relay-main Ubuntu 24.04 instance, hardens the host with nftables, fail2ban, and unattended-upgrades, then deploys Coturn plus a Coraza-enabled Caddy service with Podman Compose. Caddy handles ACME certificate issuance, HTTPS health checks, and deny-by-default web responses on the TURN hostname. Coturn handles STUN and TURN traffic directly on 3478 and 5349, reusing the certificate that Caddy stores in the shared data volume.

Repository Layout

tofu/: OpenTofu infrastructure for the static IP, VM, and GCP firewall rule.
ansible/: Host preparation and hardening for Ubuntu 24.04.
compose/: Runtime configuration for Coturn and Caddy.
docker/: Custom images for Coturn and Caddy.
.github/workflows/: CI workflows for building images and deploying the stack.

Required GitHub Secrets

R2_ACCESS_KEY_ID
R2_SECRET_ACCESS_KEY
CLOUDFLARE_ACCOUNT_ID
GCP_SA_KEY
SSH_PRIVATE_KEY
TURN_SHARED_SECRET

Recommended GitHub Variables

GCP_PROJECT
GCP_REGION
GCP_ZONE
TURN_REALM
CADDY_EMAIL

Notes

The OpenTofu S3 backend is configured at deploy time so the Cloudflare R2 endpoint does not need to be committed to the repository.
The Google provider reads service account credentials from the standard GOOGLE_APPLICATION_CREDENTIALS shell environment variable. Set it to the JSON key file path for local tofu runs.
The custom Coturn image waits for the Caddy-managed certificate for TURN_REALM to appear in the shared caddy_data volume before starting the TLS listener on 5349.
Caddy on the relay host only answers /health and returns 403 for other HTTPS requests. TURN and STUN traffic does not pass through Caddy; Coturn receives it directly through host networking.
The Ansible playbook lowers net.ipv4.ip_unprivileged_port_start to 80 so a rootless Podman-managed Caddy container can bind to 80 and 443.

DNS Setup

Create a DNS A record so the hostname used by TURN_REALM resolves to the OpenTofu-provisioned relay_ip.
If you use Cloudflare, keep that record set to DNS-only. The orange-cloud proxy does not support TURN or STUN over UDP.
Optional SRV records can advertise the default ports: _stun._udp on 3478, _turn._udp on 3478, and _turns._tcp on 5349 for the same hostname.

Local OpenTofu Usage

Export the Google credentials path and required OpenTofu variables before running tofu locally:

export GOOGLE_APPLICATION_CREDENTIALS="secret-path"
export TF_VAR_gcp_project="your-gcp-project"
export TF_VAR_gcp_region="us-west1"
export TF_VAR_gcp_zone="us-west1-b"

cd tofu
tofu init
tofu apply

network_name defaults to default, instance_name defaults to relay-main, and admin_ssh_public_key is optional unless you want SSH access provisioned on the VM.