Service loses connection to Etcd DB when pod restarts
Keeping application and database in one pod is one of the worst practices in Kubernetes. If you update application code - you have to restart pod to apply changes. So you restart database also just for nothing.
Solution is very simple - you should run application in one deployment and database - in another. That way you can update application without restarting database. In that case you can also scale app and DB separately, like add more replicas to app while keeping DB at 1 replicas or vice versa.