Can't create ipv4 clusters if ipv6 is disabled at kernel level

[marcosnils]

What happened:
Due to #1526, docker network create will constantly fail if ipv6.disable=1 is set in boot time at kernel level.

What you expected to happen:

Kind cluster to be created

How to reproduce it (as minimally and precisely as possible):

Set ipv6.disable=1 in grub, and try to create a cluster

Anything else we need to know?:

Nope, this issue has been identified already

Environment:
All

[BenTheElder]

/assign
/priority critical-urgent

workaround for now is:

docker network rm kind
docker network create -d=bridge kind

we'll fix this and cut 0.8.1

[BenTheElder]

/lifecycle active

[BenTheElder]

OK, set to repro and check exactly what behavior we can expect I think:

$ cat /proc/cmdline
BOOT_IMAGE=/boot/vmlinuz-5.4.0-28-generic root=UUID=<snip> ro quiet splash vt.handoff=7 ipv6.disable=1

[BenTheElder]

$ kind create cluster
Creating cluster "kind" ...
ERROR: failed to create cluster: failed to ensure docker network: command "docker network create -d=bridge --ipv6 --subnet fc00:f853:ccd:e793::/64 kind" failed with error: exit status 1
Command Output: Error response from daemon: Cannot read IPv6 setup for bridge br-bc6b11ad1b57: open /proc/sys/net/ipv6/conf/br-bc6b11ad1b57/disable_ipv6: no such file or directory

I think we can detect this error and abort out of trying to do an IPv6 enabled network based on that.

@marcosnils is this what you see (presumably with a different bridge name)

[marcosnils]

@marcosnils is this what you see (presumably with a different bridge name)

Exactly!

[BenTheElder]

in theory if you install (go install . or make build && cp bin/kind /somewhere/kind) this is fixed in HEAD (to confirm you'll want to delete the clusters and network first and see what happens creating a cluster)

[BenTheElder]

https://github.com/kubernetes-sigs/kind/releases/tag/v0.8.1 contains the fix