I would like to run 1 single pod of mongo db in my k8s cluster. I would be using node selector to get the pod scheduled on a specific node.

Since mongo is a database and I am using node selector, Is there any reason for me not to use k8s deployment over StatefulSet? Elaborate more on this if we should never use Deployment.

CodePudding user response：

Since mongo is a database and I am using node selector, Is there any reason for me not to use k8s deployment over StatefulSet? Elaborate more on this if we should never use Deployment.

You should not run a database (or other stateful workload) as Deployment, use StatefulSet for those.

They have different semantics while updating or when the pod becomes unreachable. StatefulSet use at-most-X semantics and Deployments use at-least-X semantics, where X is number of replicas.

E.g. if the node becomes unreachable (e.g. network issue), for Deployment, a new Pod will be created on a different node (to follow your desired 1 replica), but for StatefulSet it will make sure to terminate the existing Pod before creating a new, so that there are never more than 1 (when you have 1 as desired number of replicas).

If you run a database, I assume that you want the data consistent, so you don't want duplicate instances with different data - (but should probably run a distributed database instead).