fix: onyx nginx - use Docker DNS resolver to prevent stale upstream IPs

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

compose/bart/onyx/nginx.conf

@@ -1,19 +1,17 @@
-upstream api {
-    server api_server:8080;
-}
-
-upstream web {
-    server web_server:3000;
-}
-
 server {
     listen 80;
     server_name _;
 
+    # Use Docker's internal DNS with a short TTL so container IP changes
+    # (e.g. after docker compose up -d for a single service) are picked up
+    # without requiring an nginx reload.
+    resolver 127.0.0.11 valid=10s;
+
     client_max_body_size 100M;
 
     location /api/ {
-        proxy_pass http://api/;
+        set $api_upstream http://api_server:8080;
+        proxy_pass $api_upstream/;
         proxy_set_header Host $host;
         proxy_set_header X-Real-IP $remote_addr;
         proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
@@ -26,7 +24,8 @@ server {
     }
 
     location / {
-        proxy_pass http://web;
+        set $web_upstream http://web_server:3000;
+        proxy_pass $web_upstream;
         proxy_set_header Host $host;
         proxy_set_header X-Real-IP $remote_addr;
         proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;