generate only one upstream per worker

lib.nix

@@ -29,6 +29,7 @@ rec {
       # Subindex by resource names, listener types, and convert to upstreams
       (lib.mapAttrs (_: workers: lib.pipe workers [
         (lib.concatMap (worker: worker.settings.worker_listeners))
+        lib.lists.head # only select one listener for the worker to avoid cache thrashing
         lib.flatten
         mapListenersToUpstreamsByType
       ]))

tests/nginx-pipeline/default.nix

@@ -20,6 +20,20 @@ let
             normalSyncers = 1;
             eventPersisters = 1;
             useUserDirectoryWorker = true;
+
+            instances.auto-fed-receiver1.settings.worker_listeners = [
+              {
+                bind_addresses = [
+                  "127.0.0.2"
+                ];
+                port = 1337;
+                resources = [
+                  { compress = false;
+                    names = [ "federation" ];
+                  }
+                ];
+              }
+            ];
           };
 
           settings.server_name = "example.com";