ubuntu - Make docker use IPv4 for port binding

Question

I have docker host and inside I have one container.

The docker host is binding the port on IPv6 interface only, not on IPv4.

This is the output

tcp        0      0 0.0.0.0:22              0.0.0.0:*               LISTEN      -
tcp        0      0 0.0.0.0:55082           0.0.0.0:*               LISTEN      -
tcp        0      0 0.0.0.0:111             0.0.0.0:*               LISTEN      -
tcp6       0      0 :::80                   :::*                    LISTEN      -
tcp6       0      0 :::22                   :::*                    LISTEN      -
tcp6       0      0 :::40280                :::*                    LISTEN      -
tcp6       0      0 :::5432                 :::*                    LISTEN      -
tcp6       0      0 :::40122                :::*                    LISTEN      -
tcp6       0      0 :::36378                :::*                    LISTEN      -
tcp6       0      0 :::40543                :::*                    LISTEN      -
tcp6       0      0 :::111                  :::*                    LISTEN      -

Now I have 40122 port on host to link with port 22 on container.

I want to SSH into that container but I am not able to as its only bound to IPv6

This is my docker version Docker version 1.5.0, build a8a31ef

docker ps

201bde6c839a        myapp:latest   "supervisord -n"    3 weeks ago         Up 2 hours          0.0.0.0:40122->22/tcp, 0.0.0.0:40280->80/tcp, 0.0.0.0:40543->443/tcp   myapp

I ran using docker run -d -P -p 40122:22

netstat -tlna

tcp        0      0 0.0.0.0:80              0.0.0.0:*               LISTEN
tcp        0      0 0.0.0.0:22              0.0.0.0:*               LISTEN
tcp        0      0 127.0.0.1:3031          0.0.0.0:*               LISTEN
tcp        0      0 0.0.0.0:6379            0.0.0.0:*               LISTEN
tcp6       0      0 :::22                   :::*                    LISTEN
tcp6       0      0 :::6379                 :::*                    LISTEN

ps aux

root         1  0.0  0.8  52440 16668 ?        Ss   00:53   0:03 /usr/bin/python /usr/bin/supervisord -n
root        49  0.0  0.1  17980  3048 ?        S    01:32   0:00 bash
root        64  0.0  0.1  46632  2712 ?        S    01:32   0:00 su -l vagrant
vagrant     65  0.0  0.1  21308  3760 ?        S    01:32   0:00 -su
root       288  0.0  0.1  17980  3088 ?        S    02:01   0:00 bash
root       304  0.0  0.1  46632  2720 ?        S    02:01   0:00 su -l vagrant
vagrant    305  0.0  0.1  21304  3804 ?        S    02:01   0:00 -su
vagrant    308  0.0  3.7 429616 75840 ?        Sl+  02:01   0:05 python ./manage.py shell_plus
root       654  0.0  0.4  47596  9848 ?        S    03:12   0:01 /usr/local/bin/uwsgi --die-on-term --ini /var/www/conf/uwsgi.ini
root       655  0.0  0.3  90280  7732 ?        S    03:12   0:00 nginx: master process /usr/sbin/nginx
www-data   656  0.0  0.1  90600  3624 ?        S    03:12   0:00 nginx: worker process
www-data   657  0.0  0.1  90600  3624 ?        S    03:12   0:00 nginx: worker process
www-data   658  0.0  0.1  90600  3624 ?        S    03:12   0:00 nginx: worker process
www-data   659  0.0  0.2  90940  4500 ?        S    03:12   0:00 nginx: worker process
root       660  0.0  0.2  61372  5332 ?        S    03:12   0:00 /usr/sbin/sshd -D
root       669  0.0  0.4  37004  8892 ?        Sl   03:12   0:01 redis-server *:6379
root       856  8.0  2.8 388720 57792 ?        Sl   04:07   0:18 /usr/local/bin/uwsgi --die-on-term --ini /var/www/conf/uwsgi.ini
root       857  8.0  2.8 388720 57792 ?        Sl   04:07   0:18 /usr/local/bin/uwsgi --die-on-term --ini /var/www/conf/uwsgi.ini
root       858  8.0  2.8 388720 57792 ?        Sl   04:07   0:18 /usr/local/bin/uwsgi --die-on-term --ini /var/www/conf/uwsgi.ini
root       859  8.0  2.8 388720 57792 ?        Sl   04:07   0:18 /usr/local/bin/uwsgi --die-on-term --ini /var/www/conf/uwsgi.ini
vagrant    889  0.0  0.1  18692  2508 ?        R+   04:11   0:00 ps aux

Answer 1

As @daniel-t points out in the comment: github.com/docker/docker/issues/2174 is about showing binding only to IPv6 in netstat, but that is not an issue. As that github issues states:

When setting up the proxy, Docker requests the loopback address '127.0.0.1', Linux realises this is an address that exists in IPv6 (as ::0) and opens on both (but it is formally an IPv6 socket). When you run netstat it sees this and tells you it is an IPv6 - but it is still listening on IPv4. If you have played with your settings a little, you may have disabled this trick Linux does - by setting net.ipv6.bindv6only = 1.

In other words, just because you see it as IPv6 only, it is still able to communicate on IPv4 unless you have IPv6 set to only bind on IPv6 with the net.ipv6.bindv6only setting. To be clear, net.ipv6.bindv6only should be 0 - you can run sysctl net.ipv6.bindv6only to verify.