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

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.