This container gets containers info from rancher-metada by using rancher-gen and generates a dnsmasq configuration addressing containers.
There is a small diference from native DNS service. Instead do a round-robin when there are multiples containers for a single name, this service deliver an IP for a container in the same host.
I got annoyed when running services on 3 different hosts. The Wordpress container sometimes tries to reach Percona node running on different server, instead using the Percona node on same server.
This should not be a problem if servers are close to each other, but I had to deal with 2 servers on Canada and another one on Germany. Also, the main audience comes from Brazil.
So, to make Wordpress access Percona node close to it, I wrote this small services, copying some pieces from Rancher-Active-Proxy.
The rancher-dns-gen should run in all environment's hosts and to achieve this easily, a label io.rancher.scheduler.global: 'true' must be created. Also, this container should run in bridge mode and a fallback DNS resolver should be provided, propably falling back to 169.254.169.250.
After that, containers you want resolve by using rancher-dns-gen must be configured to use IP address of rancher-dns-gen container.
The docker-compose.yml below creates rancher-dns-gen container in all hosts of an environment.
version: '2'
services:
rancher-dns-gen:
privileged: true
image: montefuscolo/rancher-dns-gen
network_mode: bridge
dns:
- 169.254.169.250
tty: true
labels:
io.rancher.container.pull_image: always
io.rancher.scheduler.global: 'true'That is all!