Whenever the topic of instance migration comes up, it normally ends in a spirited conversation among my OpenStack peers for various reasons. So as a responsible adult, I will go on record and say instance migration is not perfect.
It has its flaws and can be quirky at best. Migration, whether live or not, has a practical use case in your OpenStack cloud. Within OpenStack, you have the capability of migrating instances from one compute node to another. You may do this for maintenance purposes and/or to rebalance the resource utilization across the cloud. Also, keep in mind that there are multiple ways to clear out a compute node for maintenance and we will cover this in more detail in Chapter 8, Deploying OpenStack Features.
Note
As mentioned earlier, the OpenStack Compute service (Nova) has the functionality to migrate instances in a traditional method and the ability to live-migrate an instance as well.
We will first examine the traditional migration method and its properties...