I started to report on this in https://bugs.archlinux.org/task/45316 but it seems that these are two separate issues, hence the new report.

After upgrading zeromq (4.0.5-1 -> 4.1.1-1) and python2-pyzmq (14.6.0-1 -> 14.6.0-2) salt-zmq does not work anymore. The client gets stuck in an infinite loop with the uninformative error message »invalid argument«. Downgrading both packages makes the same setup work again instantly.

I've tried with the just-released zeromq 4.1.2-1 and python2-pyzmq 14.6.0-3, but no dice.

I've narrowed it down to the problem only occurring if IPv6 support is enabled and used. Otherwise salt-zmq seems to work just fine.

Here's a minimal test case which I've just verified produces the problem:

1. pacstrap a minimal installation, e.g. »mkdir ~/tmp/salt-zeromq-test && pacstrap -c -d ~/tmp/salt-zeromq-test base«
2. set a password for root in side the container
3. start a container with that installation: »systemd-nspawn -bD ~/tmp/salt-zeromq-test«
4. Login in as root
5. Install salt-zmq, don't start salt just yet
6. make sure »localhost« resolves to both IPv4 and IPv6 addresses
7. configure salt-master to use IPv6, e.g. create /etc/salt/master.d/test.conf with the following content:

ipv6: true
listen: "::"

8. Start salt-master
9. configure salt-minion to use »localhost« as the master, but no IPv6 yet, e.g. create /etc/salt/minion.d/test.conf with the following content:

master: localhost

10. Start the minion; accept the minion's key with »salt-key -A«
11. Stop the minion and configure it to use IPv6 by adjusting the content of /etc/salt/minion.d/test.conf to the following content:

master: localhost
ipv6: true

12. start the minion and observe the aforementioned »invalid argument« message

If you want to verify that the downgrade fixes things: stop the master and the minion, downgrade zeromq to 4.0.5-x and python2-pyzmq to 14.6.0-1, start the master, start the minion.