HH-833: fence gateway generations across replicas (#22)

cmd/docker-gateway/proxy.go

@@ -53,7 +53,11 @@ func (registry *memoryProxyRegistry) configure(alias string, bindingVersion int6
 			(port == 0 || proxy.listener.Addr().(*net.TCPAddr).Port == port) && proxy.exit == exit && proxy.networkID == networkID {
 			return proxy.url, func() { registry.removeObject(alias, proxy) }, nil
 		}
-		return "", nil, errGenerationConflict
+		delete(registry.proxies, alias)
+		// A gateway replica may still hold the previous runtime generation. Close
+		// it before rebinding a restored listener, while removeObject's identity
+		// check keeps old cleanup callbacks from deleting the replacement.
+		closeMemoryProxy(proxy)
 	}
 	listener, err := net.Listen("tcp4", net.JoinHostPort(bindHost, strconv.Itoa(port)))
 	if err != nil {
@@ -80,10 +84,15 @@ func (registry *memoryProxyRegistry) removeObject(alias string, proxy *memoryPro
 	}
 	registry.mu.Unlock()
 	if proxy != nil {
-		_ = proxy.server.Close()
+		closeMemoryProxy(proxy)
 	}
 }
 
+func closeMemoryProxy(proxy *memoryProxy) {
+	_ = proxy.listener.Close()
+	_ = proxy.server.Close()
+}
+
 func (registry *memoryProxyRegistry) ready(alias string, port int, runtimeID string, networkIDs ...string) bool {
 	registry.mu.Lock()
 	defer registry.mu.Unlock()
@@ -120,7 +129,7 @@ func (registry *memoryProxyRegistry) remove(alias string, bindingVersion int64,
 	}
 	registry.mu.Unlock()
 	if proxy != nil {
-		_ = proxy.server.Close()
+		closeMemoryProxy(proxy)
 	}
 	return true
 }