Comment 1 for bug 1856411

I'm facing exact same problem, which seems to be intermittent. I have noticed, that /dev/shm directory inside mistral containers is not writable (even by root on the container). I believe that's because it is mounted incorrectly to system partition (and blocked by SELinux).

On undercloud with the bug:
(inside mistral_executor) df -h
...
dev/vda10 219G 42G 177G 20% /dev/shm
...

On undercloud without the bug:
(inside mistral_executor) df -h
...
shm 63M 0 63M 0% /dev/shm
...