adding a placement constraint on visualizer so it runs on a manager node

docker-stack.yml

@@ -77,6 +77,9 @@ services:
     stop_grace_period: 1m30s
     volumes:
       - "/var/run/docker.sock:/var/run/docker.sock"
+    deploy:
+      placement:
+        constraints: [node.role == manager]
 
 networks:
   frontend: