OpenStack Essex Design Summit

In this session we would like to discuss the introduction of the concept of aggregate. An aggregate is a collection of compute hosts that have access to shared capabilities (e.g. Storage, network, etc.) and allow things like hosts' zero-downtime upgrades (for example, via live migration of instances from one member of the aggregate to another), thus causing no disruption to guest instances. The concept of hierarchy of aggregates could also be explored for scalability reasons. We propose to expose such a concept to the admin of the cloud, and at the same time to keep this transparent to the end-user. In fact, the OSAPI already provide some capabilities for host management via admin extensions, but this is very crude at the moment. Further extending the concept means that putting a host into 'maintenance mode' implies that all the instances running on it can migrate onto an available host in the aggregate, thus causing no disruptions to guest instances. Bringing such capability in the API (and consequently in the orchestration infrastructure) also means that the admin can intervene on the plaform, and at the same time be agnostic of the kind of hypervisor that the host is running, which is very beneficial.