I always assumed ubuntu was brought down to prevent ubuntu servers from patching copy.fail, so that hacking group could exploit as many targets during that time as possible
There may be some processes that use this functionality ("lsof | grep AF_ALG"), but it is not that widespread AIUI, and so disabling it should not be an issue for the vast majority of systems.
copy.fail patches can be applied with minimum downtime, and a VM reboots in 30 seconds, tops, regardless of size. I believe all the apex servers are configured as HA to keep the load distributed, so normal users won't feel anything when copy.fail is patched.
Our users didn't feel a thing when we rolled out the patches.
But the Ubuntu update servers are necessary to serve the update. Taking them down prevents the users from downloading the update. I don't know whether the update servers were affected though.
On Ubuntu copy.fail could be mitigated against with some modprobe(8) config tweaks:
There may be some processes that use this functionality ("lsof | grep AF_ALG"), but it is not that widespread AIUI, and so disabling it should not be an issue for the vast majority of systems.