Federating Clusters for Zero-Downtime Kubernetes
a month ago
- Linkerd's multicluster extension enables three modes: federated, flat mirroring, and gateway mirroring, which can coexist on the same set of linked clusters.
- Federated mode allows services with the same name across clusters to be unioned into a single load-balanced endpoint, providing automatic failover with no application changes.
- Flat mirroring enables explicit routing to remote services by name, with traffic going directly to remote pods, requiring a flat network with pod IPs routable.
- Gateway mirroring routes traffic through a gateway IP, allowing cross-cluster connectivity without requiring pod-to-pod network reachability.
- A demo setup across three GKE clusters demonstrates all three modes, with VPC peering for flat networking and a shared trust anchor for cross-cluster mTLS.
- Chaos testing shows that federated services automatically redistribute traffic when a cluster fails, while mirrored services require client-side failover handling.
- Key operational considerations include non-overlapping CIDRs, proper VPC peering route exchange, controller count per link, and careful cluster node configuration to control costs.
- A decision framework helps choose the appropriate mode based on client needs, network constraints, and failover requirements.