Arch Linux

lapsio

Member

From: Warsaw

Registered: 2015-09-30

Posts: 50

Predictable interface names became not-so-predictable?

I'm using 2 Arch NGINX servers in HA cluster using VRRP. Initially it was one machine, then I created second machine by installing clean Arch, installing the same packages and copying config files. It seemed a little bit suspicious to me from very beginning that original machine used "ens3" interface and new machine got "enp3s0" even though they were almost identical machines on hardware level (KVM guests with nearly identical qemu command line, only different hard drives config)

Today after Arch update on BACKUP machine, of course I performed standard test procedure (interface down) to make sure that failover works however when after around 5 seconds NGINX still didn't come back online I knew something wasn't right.

It turns out Arch after update changed interface naming scheme from enp3s0 to ens3 like on original server and It made me REALLY, REALLY worried about predictability and reliability of this setup. In fact I thought that both of those schemes are "Predictable interface names" they're just selected basing on some specific hardware config but it seems they're not really the same category.

So when systemd or whatever uses following naming schemes? How can I enforce uniform naming scheme to be sure that it won't get screwed  after update?

Last edited by lapsio (2018-03-28 18:15:02)

progandy

Member

Registered: 2012-05-17

Posts: 5,196

Re: Predictable interface names became not-so-predictable?

This was a bug in systemd. It should be fixed now with 238.51-1
https://bbs.archlinux.org/viewtopic.php?id=235307

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amish

Member

Registered: 2014-05-10

Posts: 470

Re: Predictable interface names became not-so-predictable?

@lapsio - when u installed fresh version of arch linux, it came with buggy version of systemd.

so instead of predicted ens3 it named it as enp3s0

But after updating systemd, bug was fixed and the predictable name was back.

Last edited by amish (2018-03-29 02:58:16)