Node Affinity & Cluster Topology

M3DB was built with failure tolerance as a core feature. M3DB’s isolation groups allow shards to be placed across failure domains such that the loss of no single domain can cause the cluster to lose quorum. More details on M3DB’s resiliency can be found in the .

By leveraging Kubernetes’ node affinity and M3DB’s isolation groups, the operator can guarantee that M3DB pods are distributed across failure domains. For example, in a Kubernetes cluster spread across 3 zones in a cloud region, the configuration below would guarantee that no single zone failure could degrade the M3DB cluster.

In addition to allowing pods to be assigned to certain nodes via node affinity, Kubernetes allows pods to be repelled from nodes through taints if they don’t tolerate the taint. For example, the following config would ensure:

1. Pods are spread across zones.

The examples so far have focused on multi-zone Kubernetes clusters. Some users may only have a cluster in a single zone and accept the reduced fault tolerance. The following configuration shows how to configure the operator in a zonal cluster.

If there are no failure domains available, one can have a cluster with no affinity where the pods will be scheduled however Kubernetes would place them by default: