fix: nginx health check probes backend instead of static 200

docker/README.md

@@ -83,11 +83,10 @@ The Dockerfile creates empty `/app/models`, `/app/lora`, `/app/output` directori
 
 ## Health Check
 
-The nginx proxy responds with `200 OK` on `GET /` for load balancer health checks (AWS ALB, etc.). This is separate from the WebUI at `/webui/`.
+The nginx proxy forwards `GET /` to the training-webui backend, so load balancer health checks (AWS ALB, etc.) reflect real application health — returning 502 when the backend is down. This is separate from the WebUI at `/webui/`.
 
 ```bash
 curl http://localhost/
-# OK
 ```
 
 ## Direct Access (no proxy)
@@ -153,5 +152,5 @@ docker compose -f docker/docker-compose.yml logs -f training-webui
 - **OOM errors**: Reduce batch size in the WebUI or use a GPU with more VRAM.
 - **WebUI not accessible**: Check that port 80 (nginx) or 7860 (direct) isn't blocked by a firewall.
 - **WebSocket errors behind proxy**: Ensure your proxy forwards `Upgrade` and `Connection` headers (the included nginx.conf handles this).
-- **Health check failing**: Ensure nginx is running — `curl http://localhost/` should return `OK`.
+- **Health check failing**: Ensure the training-webui container is running — `curl http://localhost/` proxies to the backend and returns 502 if it's unreachable.
 - **Mixed-content / audio not playing over HTTPS**: The nginx config uses `map $http_x_forwarded_proto` to pass the correct protocol through to Gradio. This ensures `https://` file URLs are generated when accessed via HTTPS through a load balancer.

docker/nginx.conf

@@ -15,8 +15,11 @@ server {
 
     # Health check for load balancers (AWS ALB, etc.)
     location = / {
-        return 200 'OK\n';
-        add_header Content-Type text/plain;
+        proxy_pass http://training-webui:7860/;
+        proxy_set_header Host $host;
+        proxy_read_timeout 5s;
+        proxy_connect_timeout 3s;
+        access_log off;
     }
 
     location = /manifest.json {