A common way of dealing with the recovery from a full system failure, such as a power outage of a data center, is to assign each service a priority, and restore in order. Table. Example service restoration priority list shows an example.
|1||Internal network connectivity|
|2||Backing storage services|
|3||Public network connectivity for user virtual machines|
|5||User virtual machines|
|10||Message queue and database services|
|21||Image Catalog and Delivery services|
Use this example priority list to ensure that user-affected services are restored as soon as possible, but not before a stable environment is in place. Of course, despite being listed as a single-line item, each step requires significant work. For example, just after starting the database, you should check its integrity, or, after starting the nova services, you should verify that the hypervisor matches the database and fix any mismatches.