why can't the first container "see" the later containers - apache-zookeeper

Question

I have a series of containers that are started by docker-compose. Specifically they are multiple zookeeper containers:
zk1:
image: seven10/zookeeper:3.4.6
container_name: zk1
hostname: zk1
restart: always
ports:
- "2181:2181"
- "2888:2888"
- "3888:3888"
environment:
- ZOOKEEPER_ID=1
net: ${MY_NETWORK_NAME}
volumes:
- /seven10/zk/zk1/data:/opt/zookeeper-3.4.6/data
zk2:
image: seven10/zookeeper:3.4.6
container_name: zk2
restart: always
hostname: zk2
ports:
- "2182:2181"
- "2889:2888"
- "3889:3888"
environment:
- ZOOKEEPER_ID=2
net: ${MY_NETWORK_NAME}
volumes:
- /seven10/zk/zk2/data:/opt/zookeeper-3.4.6/data
zk3:
image: seven10/zookeeper:3.4.6
container_name: zk3
hostname: zk3
restart: always
ports:
- "2183:2181"
- "2890:2888"
- "3890:3888"
environment:
- ZOOKEEPER_ID=3
net: ${MY_NETWORK_NAME}
volumes:
- /seven10/zk/zk3/data:/opt/zookeeper-3.4.6/data
So when I go to start the containers, zk1 gives me this warning at the start:
WARN [WorkerSender[myid=1]:QuorumCnxManager#382] - Cannot open channel to 3 at
election address zk3:3888
java.net.UnknownHostException: zk3
but then doesn't say anything else about zk3 after a couple of seconds.
However, zk1 gives the following error for zk2 continuously:
2016-02-18 15:28:57,384 [myid:1] - WARN [QuorumPeer[myid=1]/0:0:0:0:0:0:0:0:2181:Learner#233] - Unexpected exception, tries=0, connecting to zk2:2888
java.net.UnknownHostException: zk2
zk2 doesn't say ANYTHING ever about zk1, but briefly complains with the "cannot open channel" error for zk3.
zk3 doesn't every mention zk1 or zk2.
So the big problem is that zk1 can't find zk2 ever. It just spams the logs and refuses connections from kafka. Why is this so and how should I go about solving this problem?
My dev box is using docker version 1.9.1 and docker-compose version 1.5.1 on ubuntu 14.04 (Mint Rafello I think?), although the target environment will be ubuntu 15.10.

Answer 1

Does your host system know how to link zk1/2/3 to an IP address? If you're launching all three servers on the same node, you should use localhost as the host name (the server name should still be unique)