Applications with high availability requirements must be deployed to multiple clusters to ensure reliability. Historically, this has been done by pulling nodes from other availability zones into the same cluster. However, if the cluster failed, the application would still become unavailable. Rancher’s support for multi-cluster applications is a significant step forward, solving this problem by allowing users to select the application and the target clusters, providing cluster specific data. Rancher then initiates deployment to those clusters.
Source: DevOps Journal