Comment 12 for bug 1887589

Waiting submitter to help reproduce the issue manually, and give more info about the issue.
BTW, for the mariadb error log message, it also show in normal log. The reason is that, when do host-swact or controller reboot, there will be some time for mariadb to switch between nodes, and cause mariadb service not available. In my test, nova scheduler will retry and always success to create VM at the end.
So I cannot determine what cause the VM failure yet from log files.