In docker containers, once the process that is set to run at the start shutdowns itself, the container will also be terminated.
preStop hook helps with this: it tells mongod to shutdown itself, it does so gracefully (unless timed out), and once mongod is stopped the container also shuts down itself.
Though I hoped to be wrong, as you too mentioned in your github follow up post, it seems container’s network is cut off early. This might be a bug in k8s, or it might be set somewhere else in it so pod resources stay up until main container process exits/dies.
Please keep us updated.