How to assign IPv6 address with docker-compose

Question

I am using docker 1.12.1 on Ubuntu 16.04, and docker-compose 1.8.1. I am trying to get the Compose file from https://docs.docker.com/compose/compose-file/#ipv4-address-ipv6-address to run. For reference, I created docker-compose.yml with the following content:

version: '2'

services:
  app:
    image: busybox
    command: ifconfig
    networks:
      app_net:
        ipv4_address: 172.16.238.10
        ipv6_address: 2001:3984:3989::10

networks:
  app_net:
    driver: bridge
    driver_opts:
      com.docker.network.enable_ipv6: "true"
    ipam:
      driver: default
      config:
      - subnet: 172.16.238.0/24
        gateway: 172.16.238.1
      - subnet: 2001:3984:3989::/64
        gateway: 2001:3984:3989::1

Now, running docker-compose up produces

Creating network "tmp_app_net" with driver "bridge"
Creating tmp_app_1
Attaching to tmp_app_1
app_1  | eth0      Link encap:Ethernet  HWaddr 02:42:AC:10:EE:0A  
app_1  |           inet addr:172.16.238.10  Bcast:0.0.0.0  Mask:255.255.255.0
app_1  |           inet6 addr: fe80::42:acff:fe10:ee0a/64 Scope:Link
app_1  |           UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
app_1  |           RX packets:4 errors:0 dropped:0 overruns:0 frame:0
app_1  |           TX packets:1 errors:0 dropped:0 overruns:0 carrier:0
app_1  |           collisions:0 txqueuelen:0 
app_1  |           RX bytes:520 (520.0 B)  TX bytes:90 (90.0 B)
app_1  | 
app_1  | lo        Link encap:Local Loopback  
app_1  |           inet addr:127.0.0.1  Mask:255.0.0.0
app_1  |           inet6 addr: ::1/128 Scope:Host
app_1  |           UP LOOPBACK RUNNING  MTU:65536  Metric:1
app_1  |           RX packets:0 errors:0 dropped:0 overruns:0 frame:0
app_1  |           TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
app_1  |           collisions:0 txqueuelen:1 
app_1  |           RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)
app_1  | 
tmp_app_1 exited with code 0

The IPv6 address is not assigned.

I already tried:

1. Starting the docker daemon with --ipv6
2. Starting the docker daemon with --ipv6 --fixed-cidr-v6="2001:3984:3989::/64"
   • Note that docker run -it busybox ifconfig actually gives me an IPv6 address here (from the --fixed-cidr subnet which is assigned to the default bridge network)
3. Using my actual IPv6 subnet instead of the one from the code example, and repeating 2. with this subnet

No success. Any ideas?

Answer 1

It turns out this is indeed a docker-compose bug that is going to be fixed in 1.9.0.

Meanwhile, there is a workaround by creating a custom network with the docker network command:

docker network create --subnet=172.16.2.0/24 --gateway=172.16.2.1 --ipv6 --subnet=<myV6Network/subnet> dockerbridge

... which can then be made available inside docker-composed.yml by writing

networks:
  dockerbridge:
    external:
      name: dockerbridge