Container on swarm not able to connect to the internet (when ports published)

Docker Engine Swarm
1

Hi,
I deploy services through docker stack deploy in a yaml file where each service is on an overlay network, as below:

services:
  a:
    image: org/a:latest
    networks:
      - network_overlay
  b:
    image: org/b:latest
    ports:
      - "8000:8000"
   networks:
      - network_overlay

networks:
  network_overlay:
      driver: overlay
      attachable: true

When I do curl on a it works, on b I get: curl: (6) Could not resolve host:

As seen above the difference between a and b is only some ports published.
Is there a way where a service has a published port but can also access the internet?

2

Since you quoted compose file has an indentation error, I’m surprised it works at all. Maybe Swarm ignores it somehow. Try to fix the indentaion of the network keyword .

3

When copied the indentation got corrupt, obviously original yaml file is not.

4

What you experience is not caused by published ports. There must be an underlying problem that causes this behavior.

Is this a multi node setup, and are both containers running on different nodes? Does it happen if both run on the same node? It might be a problem with the overlay network.

5

It is a multi node setup, however:

  • both services are deployed to the same node, one works the other doesn’t
  • in the above example even on the same service b, if I remove port statement I can do curl
  • I tried:
    docker run --rm --network network_overlay nginx:alpine ping google.com,
    to rule out network issue.
6

The last point seems not consistent, earlier you write the expose ports breaks Internet access. Here no port is used.

And you don’t write if the test was successful or a failure. Does only service b have the problem?

7

The teat is successful meaning that i successfully can curl so I was able to rule out network isn’t the issue.
When ports are not exposed on service b it is able to access the internet. The only difference is expose or not.