Comment 4 for bug 1822541

Have confirmed this is related to this bug:

https://bugs.launchpad.net/oslo.cache/+bug/1812935

If cache is disabled this is potentially a more suitable workaround, allowing HA to function, but I do not know the full impact of doing this.

/etc/nova/nova.conf has [cache] section with enabled = true, this can be changed to false and nova-conductor restarted - instances can then be created successfully.