We’ve created a third availability zone named eu-west-1c in our region for you to use. Why should I use three zones? Using three zones is recommended to create an optimal multi-site failover cluster. Network problems can cause serious issues between cluster nodes. When a subset of nodes is unable to communicate with one another but continue to operate independently, data can become out of sync. To prevent this “split brain” situation a quorum, majority vote, is established authorising only one subset of nodes to continue operations, providing safe automatic failover.