Apart from local clusters, Pacemaker also supports multi-site clusters. That means you can have multiple, geographically dispersed sites, each with a local cluster. Failover between these clusters can be coordinated manually by the administrator, or automatically by a higher-level entity called a Cluster Ticket Registry (CTR).
15.1. Challenges for Multi-Site Clusters
Typically, multi-site environments are too far apart to support synchronous communication and data replication between the sites. That leads to significant challenges:
How do we make sure that a cluster site is up and running?
How do we make sure that resources are only started once?
How do we make sure that quorum can be reached between the different sites and a split-brain scenario avoided?
How do we manage failover between sites?
How do we deal with high latency in case of resources that need to be stopped?
In the following sections, learn how to meet these challenges.
