title: Docker stack deploy using overlay network - inconsistent behavior
body: <p>I am deploying 2 containers (application and SQL) to the same network using a docker-compose.yml file (Swarm stack deploy).
  Most of the time, the application has no problems talking to the SQL via its host name as a datasource in the connection string.</p>
  
  <p>However, there are times where it simply can't find it. In order to debug it, I have verified that the overlay network is indeed created in each node, and when inspecting the network on each node, I see that the container does belong to this network.</p>
  
  <p>Moreover, when I run <code>docker exec</code> command to enter the application container, I try to send a ping to the SQL container, and the host name does resolves to the correct IP, but still there is no response back.</p>
  
  <p>This is extremely frustrating, as it only occurs from time to time.
  Any suggestions of how to debug the issue ?</p>
  
  <pre><code>version: '3.2'
  services:
    sqlserver:
     image: xxxx:5000/sql_image
     hostname: sqlserver
     deploy: 
       endpoint_mode: dnsrr
     networks:
        devnetwork:
          aliases:
              - sqlserver
  
    test:
      image: xxxx:5000/test
      deploy: 
       endpoint_mode: dnsrr
      deploy:
       restart_policy:
          condition: none
       resources:
          reservations:
            memory: 2048M
      networks:
        - devnetwork
  
  networks:
      devnetwork:
          driver: overlay
  </code></pre>