如何从docker容器中获取外部主机ip地址

Question

We are transitioning (we hope) from CoreOS to CentOS, from fleet to swarm. I need to determine the ip address of the machine running docker from inside the container.

The problem is that we use nginx to determine which of the machines in our docker cluster runs which service. To make this work we need the container to be able to post to our etcd repository the ip address of the machine upon which it is located. Everything I have seen so far has been able to get me to a 172.17.0.1 ip address for the external machine, but ALL of our containers on ALL of our dockers will have that private address. I need an EXTERNAL address that nginx may use to get to the service.

I could use the '--hostname ip ... ' option or the '-e EXT_HOST_IP= ip ... ' option to set an ip address, but if I include these in the 'docker run' command, the shell processing the docker command will expand the 'ip...' and return the ip address of the current machine -- NOT the machine upon which swarm will eventually run the container.

The best I have come up with so far is to create a file/directory on the host machine that contains the ip address of the host machine. I can then use the docker '-v' option to mount the directory inside the container, and get the ip address from that. It just seems like there should be an easier way to do this.

Answer 1

Swarm issue 1106 mentions in a recent answer

inside swarm I can get the ip of the host machine like so

ip route | awk '/default/ { print $3 }' 

Which is fine for many purposes.

But when I talk to that IP I need to use the proper dns name for TLS to work.