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As Florian Haas has pointed out in my previous post’s comment, our shared storage configuration requires special precautions to avoid corruption of data when two hosts connected via DRBD try to manage LVM volumes simultaneously. Generally, these precautions concern locking LVM metadata operations while running DRBD in ‘dual-primary’ mode. Let’s examine it in detail. The [...]

Today, I want to take a look at some possible issues that may be encountered while using OpenStack. The purpose of this topic is to share our experience dealing with the hardware or software failures which definitely would be faced by anyone who attempts to run OpenStack in production.

Software issue
Let’s look at the simplest, but possibly the most frequent issue. For example, if we need to upgrade the kernel or software that will require a host reboot on one of the compute nodes, the best decision in this case is to migrate all virtual machines running on this server to other compute nodes. Unfortunately, sometimes it may be impossible due to several reasons, such as lack of shared storage to perform migration or cpu/memory resources to allocate all VMs. The only option is to shut down virtual machines for the maintenance period. But how should they be started correctly after being rebooted? Of course, you may set the special flag in nova.conf and instances will start automatically on the host system boot: