7

how is it possible to resolve names defined in Docker host's /etc/hosts in containers? Containers running in my Docker host can resolve public names (e.g. www.ibm.com) so Docker dns is working fine. I would like to resolve names from Docker hosts's (e.g. 127.17.0.1 smtp) from containers.

My final goal is to connect to services running in Docker host (e.g. smtp server) from containers. I know I can use the Docker Host IP (127.17.0.1) from containers, but I thought that Docker would have used the Docker host /etc/hosts to build containers's resolve files as well.

I am even quite sure I have seen this working a while ago... but I could be wrong.

Any thoughts?

Giovanni

gxvigo
  • 787
  • 4
  • 10
  • 20
  • Here [How can you make the docker container use the host machine /etc/hosts file](http://stackoverflow.com/questions/32079364/how-can-you-make-the-docker-container-use-the-host-machines-etc-hosts-file) is similar problem, with accepted resolution. – itiic Mar 28 '17 at 10:59

2 Answers2

12

Check out the --add-host flag for the docker command: https://docs.docker.com/engine/reference/run/#managing-etchosts

$ docker run --add-host="smtp:127.17.0.1" container command

In Docker, /etc/hosts cannot be overwritten or modified at runtime (security feature). You need to use Docker's API, in this case --add-host to modify the file.

For docker-compose, use the extra_hosts option.

For the whole "connect to services running in host" problem, see the discussion in this GitHub issue: https://github.com/docker/docker/issues/1143.

The common approach for this problem is to use --add-host with Docker's gateway address for the host, e.g. --add-host="dockerhost:172.17.42.1". Check the issue above for some scripts that find the correct IP and start your containers.

jdno
  • 4,104
  • 1
  • 22
  • 27
0

You can setup on host simple DNS server, and in container setup /etc/resolve.conf to Docker host DNS server.

For example in dnsmasq you can add addn-hosts=/etc/hosts to config file. So container, by using Docker host DNS server, will be able to resolve hosts /etc/hosts.

komar
  • 861
  • 5
  • 8