link docker containers and use wildcard subdomains

Question

I have two docker containers (container_one and container_two), one is linked to the other container_one >>link>> container_two.

when i run a curl command from within container_one using the address: http://container_two/index.php the curl command executes successfully as expected.

however, i would like to introduce a wildcard subdomain so that i can attach any number of subdomains to container_two (eg: site1.container_two, site2.container_two, *.container_two, etc). Obviously, calling a curl command from container_one: http://site1.container_two/index.php does not work with linking alone.

Does anyone know how this would be possible with a docker run command or perhaps some other way?

Answer 1

Basically, you cannot do this with just --link flags, because --link adds an entry to the /etc/hosts file to facilitate this inter-container communication, and /etc/hosts files do not support wildcard entries.

However, you could set up a DNS server on your container_one, and set up your wildcard host (or subdomain records) on that DNS server to point to your container_two (and forward all other requests to your actual DNS for all other hostnames), and then specify --dns=127.0.0.1 in your docker run command for container_one. This seems a bit hacky, but what happens is that container_one will then use 127.0.0.1 (localhost) when it encounters a hostname it does not recognize in /etc/hosts, and the DNS on container_one will point to container_two for subdomains (and all other requests forwarding to your external DNS infrastructure).

You can find more information about this in the documentation. Good luck!