fix(nginx): re-resolve upstreams so a container restart cannot break ingest

docker-compose.yml

@@ -601,11 +601,19 @@ services:
     ports:
       - "$SENTRY_BIND:80/tcp"
     image: "nginx:1.31.4-alpine"
+    environment:
+      # nginx.conf needs the container engine's DNS address, which differs per engine.
+      # The image reads it from /etc/resolv.conf into NGINX_LOCAL_RESOLVERS and substitutes
+      # it into templates, so nginx.conf is mounted as one and rendered over the image default.
+      # The filter keeps envsubst away from the nginx runtime variables in the config.
+      NGINX_ENTRYPOINT_LOCAL_RESOLVERS: 1
+      NGINX_ENVSUBST_OUTPUT_DIR: /etc/nginx
+      NGINX_ENVSUBST_FILTER: "^NGINX_LOCAL_RESOLVERS$$"
     volumes:
       - type: bind
         read_only: true
         source: ./nginx.conf
-        target: /etc/nginx/nginx.conf
+        target: /etc/nginx/templates/nginx.conf.template
       - sentry-nginx-cache:/var/cache/nginx
       - sentry-nginx-www:/var/www
     healthcheck:

nginx.conf

@@ -65,13 +65,27 @@ http {
 	proxy_read_timeout 90s;
 	proxy_send_timeout 5s;
 
+	# Without "resolve", nginx looks the service names up once at startup and keeps that address
+	# for the life of the worker process. Docker does not guarantee a container the same address
+	# across starts, so nginx can end up proxying to a container that no longer owns it and
+	# answer every request with 502 until someone restarts nginx by hand.
+	# "resolve" needs a resolver, and the container engine's own DNS is the only thing on a Compose
+	# network that knows the service names. Its address differs per engine -- 127.0.0.11 on Docker,
+	# the network gateway on Podman -- so it is read from /etc/resolv.conf at startup by
+	# /docker-entrypoint.d/15-local-resolvers.envsh, which is why this file is a template.
+	# There are no AAAA records worth waiting for on a Compose network.
+	resolver ${NGINX_LOCAL_RESOLVERS} valid=10s ipv6=off;
+
 	upstream relay {
-		server relay:3000;
+		# "resolve" requires the upstream group in shared memory, hence "zone".
+		zone relay 64k;
+		server relay:3000 resolve;
 		keepalive 2;
 	}
 
 	upstream sentry {
-		server web:9000;
+		zone sentry 64k;
+		server web:9000 resolve;
 		keepalive 2;
 	}