fix: defer API DNS resolution in nginx

docker/nginx.conf

@@ -4,8 +4,15 @@ server {
   root /usr/share/nginx/html;
   index index.html;
 
+  # Docker Swarm may start this container before the API service receives a DNS
+  # record. Resolving through Docker DNS at request time keeps Nginx alive while
+  # the API starts or is replaced during a rolling deployment.
+  resolver 127.0.0.11 ipv6=off valid=10s;
+  resolver_timeout 5s;
+  set $api_upstream api;
+
   location /api/ {
-    proxy_pass http://api:3001;
+    proxy_pass http://$api_upstream:3001;
     proxy_http_version 1.1;
     proxy_set_header Host $host;
     proxy_set_header X-Real-IP $remote_addr;