Depends on what kind of redundancy you want. You can achieve quite a decent uptime for a single instance with local redundancy, process health watchdogs to rest

Depends on what kind of redundancy you want. You can achieve quite a decent uptime for a single instance with local redundancy, process health watchdogs to restart things, crash isolation… Yes, some people will need a cluster with no downtime on failure events, but the clustering itself adds complexity and can even increase downtime if it causes problems. For example, a single machine can’t have load balancer issues, or replication errors. Also, you’re assuming an active-active redundancy scheme, which might not be always necessary, and not counting the cost of the elements required to support the cluster.