A single Kubernetes cluster provides an extremely flexible platform to design any complex distributed system. This also includes statefull workloads such as databases.

For many scenarios a single cluster is enough.

• scaleability achieved by increasing number of nodes from a node pool

  Kubernetes 1.24 supports clusters up to 5000 nodes

• workload isolation using namespaces

When are multiple clusters needed.

• there are already existing clusters that need to talk to each other
• strict security and workload isolation rules
• cost factors

Good comparison

• Submariner
• Skupper
• KubeCarrier
• Linkerd
• Cilium Cluster Mesh
• Multi-Cluster Service APIs
• Consul Connect
• Liqo
• Yggdrasil
• KEP-1645