This document discusses building a fault tolerant and high availability architecture for OpenStack. It proposes using master-master clustering for MySQL, disk-level replication for databases using DBRD, session-level replication for RabbitMQ, and high availability for networking, Horizon dashboard, and all components. Pacemaker relies on Corosync for reliable cluster communications to provide high availability. Required packages include pacemaker, corosync, cluster-glue, and resource-agents. Architectures show implementing DBRD and Pacemaker/Corosync for MySQL and RabbitMQ high availability between cloud controllers. Nova and cloud controllers would have recovery modes to handle failures.