How to access a container/service port in swarm without publishing the port to the outside world?

Question

It is possible to docker-compose to forward a port to the container from localhost only, by writing the desired ports configure in docker-compose.yml, e.g. 127.0.0.1:8080:80.

In docker swarm this does not work and the published port is visible from the internet.

How then can I access the container port only from localhost without opening the port to the internet?

I tried configuring iptables to deny connection to port iptables -A INPUT -p tcp --dport 5432 -j DROP, but because of the settings from docker for iptables, that didn't work.

Answer 1

The container can be accessed via the ip which belongs to the docker_gwbridge interface.

I was able to find out the ip address of the container on the docker_gwbridge interface by running the ifconfig command in the container itself:

$ docker exec <container-id> ifconfig

This way the container can be accessed from host machine for example by 172.18.0.2:5432, without having to publish port 5432.

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Trying to find out the ip address via docker inspect <container-id> (or <service-name> or <network-id>) in swarm services did not lead to the desired result, because the ip from the docker_gwbridge interface was not displayed there. And the "internal" ip (something like 10.0.4.6) was not available from host machine.