Fix nginx configuration syntax errors

- Move proxy_set_header directives inside location blocks
- Add DNS resolver for dynamic upstream resolution
- Improve fallback configuration in docker-compose
- Add config validation before starting nginx

This should resolve the nginx startup failures.

docker-compose.zero-downtime-fixed.yml

@@ -31,8 +31,11 @@ services:
         # Remove default nginx configuration files to prevent conflicts
         rm -rf /etc/nginx/conf.d/*
         
-        if [ ! -f /etc/nginx/nginx.conf ]; then
-          echo 'Creating fallback nginx configuration...'
+        # Test the main config first
+        if nginx -t -c /etc/nginx/nginx.conf 2>/dev/null; then
+          echo 'Using main nginx configuration'
+        else
+          echo 'Main config failed, creating fallback nginx configuration...'
           cat > /etc/nginx/nginx.conf << 'EOF'
       events {
           worker_connections 1024;
@@ -56,6 +59,9 @@ services:
                   proxy_set_header X-Real-IP \$remote_addr;
                   proxy_set_header X-Forwarded-For \$proxy_add_x_forwarded_for;
                   proxy_set_header X-Forwarded-Proto \$scheme;
+                  proxy_connect_timeout 5s;
+                  proxy_send_timeout 60s;
+                  proxy_read_timeout 60s;
               }
           }
       }