ubuntu@manager1:~$ cat /etc/resolv.conf 
# Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)
# DO NOT EDIT THIS FILE BY HAND — YOUR CHANGES WILL BE OVERWRITTEN
nameserver 172.100.0.21
search eu-west-1.compute.internal

if I change resolv.conf to ^ example and restart docker service, I have this in logs:

2016/08/25 18:53:24 [WARN] agent: http request failed ‘http://6ad1e83e5d62:8080/health': Get http://6ad1e83e5d62:8080/health: dial tcp: lookup 6ad1e83e5d62 on 172.100.0.21:53: read udp 172.100.0.21:42621->172.100.0.21:53: read: connection refused