Since a while I am using nftables for my firewalling needs. My nftables.conf has some prerouting settings. After playing with docker, I had the issue that I was no longer able to reload my nftables:
/etc/nftables.conf:12:9-18: Error: Could not process rule: Device or resource busy
chain prerouting {
^^^^^^^^^^
Also disabling the Docker service did not help. It seems that the kernel module iptable_nat needs to be removed, but this is currently in use:
# rmmod iptable_nat rmmod: ERROR: Module iptable_nat is in use
There are some iptable rules/chains active which prevent the module from unloading. By clearing the iptable configuration, especially the nat table, it is possible to remove iptable_nat and then using nftables again.
iptables -F iptables -X iptables -t nat -F iptables -t nat -X iptables -t mangle -F iptables -t mangle -X