OpenStack infrastructure high availability relies on the Pacemaker cluster stack, the state-of-the-art high availability and load balancing stack for the Linux platform. Pacemaker is storage and application-agnostic, and is in no way specific to OpenStack.
Pacemaker relies on the Corosync messaging layer for reliable cluster communications. Corosync implements the Totem single-ring ordering and membership protocol. It also provides UDP and InfiniBand based messaging, quorum, and cluster membership to Pacemaker.
Pacemaker interacts with applications through resource agents (RAs), of which it supports over 70 natively. Pacemaker can also easily use third-party RAs. An OpenStack high-availability configuration uses existing native Pacemaker RAs (such as those managing MySQL databases or virtual IP addresses), existing third-party RAs (such as for RabbitMQ), and native OpenStack RAs (such as those managing the OpenStack Identity and Image Services).
