I would like to run a single pod of Mongo db in my Kubernetes 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 Kubernetes Deployment over StatefulSet? Elaborate more on this if we should never use Deployment.
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).