docker / kubernetes breaks Proxmox QEMU KVM Bridge VMs

It's best not to mix the two technologies. Here is how to fix things but break Docker.

If you do an iptables -L you will notice even if you deleted all the Docker chains that the iptables FORWARD policy is enabled and is set to drop, this causes your VMs to not have networking, at least not outside the host machine.

`Chain FORWARD (policy DROP) target prot opt source destination`

Here is how to fix everything:

If your bridge interface is not br0 like below change it (eg. if it's vmbr0 then change it to that).

iptables -A FORWARD -p all -i br0 -j ACCEPT

or for blanket all

iptables --policy FORWARD ACCEPT

Now you'll see it has policy ACCEPT so the VM traffic will work:

Chain FORWARD (policy ACCEPT) target prot opt source destination

Delete the Docker chains

iptables -X DOCKER-ISOLATION-STAGE-1

iptables -X DOCKER-ISOLATION-STAGE-2

iptables -X DOCKER

iptables -X DOCKER-USER

What Docker did to our machine with iptables:

root@nfs01:# iptables -L Chain INPUT (policy ACCEPT) target prot opt source destination Chain FORWARD (policy DROP) target prot opt source destination Chain OUTPUT (policy ACCEPT) target prot opt source destination Chain DOCKER (0 references) target prot opt source destination Chain DOCKER-ISOLATION-STAGE-1 (0 references) target prot opt source destination Chain DOCKER-ISOLATION-STAGE-2 (0 references) target prot opt source destination Chain DOCKER-USER (0 references) target prot opt source destination

root@nfs01:# iptables -X DOCKER
root@nfs01:# iptables -X DOCKER-ISOLATION-STAGE-1
root@nfs01:# iptables -L^C
root@nfs01:# ping 192.168.11.240^C
root@nfs01:# iptables -X DOCKER-ISOLATION-STAGE-2
root@nfs01:# iptables -L
Chain INPUT (policy ACCEPT)
target     prot opt source               destination

Chain FORWARD (policy DROP)
target     prot opt source               destination

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination

Chain DOCKER-USER (0 references)
target     prot opt source               destination
root@nfs01:# iptables -X DOCKER-USER
root@nfs01:# iptables -L
Chain INPUT (policy ACCEPT)
target     prot opt source               destination

Chain FORWARD (policy DROP)
target     prot opt source               destination

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination