dockerdiscovery: use Compose project name for service name (which might be used for ACL)

this is to provide more stable identifiers so if we use ACL rules the identifiers don't
change all the time.
(for example Docker's newer Go-based Compose generation changed how the container names are formatted)

Author: joonas-fi

pkg/erdiscovery/dockerdiscovery/docker.go

@@ -296,11 +296,22 @@ func discoverDockerContainers(
 			continue
 		}
 
+		// service name is kind of important as it might be used in different kinds of identifiers.
+		// maybe in ACLs, to query logs etc.
+		//
+		// let's try to use the most stable thing. the container name is not great, as Compose laid the names like:
+		// - /calendarserver_baikal_1
+		// then they arbitrarily changed it from underscores to dashes:
+		// - /calendarserver-baikal-1
+		//
+		// so looks like the compose project name is more stable and reliable, only after that prefer the container name.
+		//
 		// use swarm service name if defined, so we get stable names ("baikal_baikal") instead of
 		// "/baikal_baikal.1.mifsjkoi93gwh9yg89c51va0t" for Swarm-based containers. normally we don't
-		// use this discoverDockerContainers() but Swarm, but if we use docker_gwbridge this is how
+		// use this discoverDockerContainers() for Swarm, but if we use docker_gwbridge this is how
 		// we discover conainers outside of Swarm network contexts
 		serviceName := coalesce(
+			container.Labels["com.docker.compose.project"],
 			container.Labels["com.docker.swarm.service.name"],
 			container.Names[0])