Problem

I have a project to do, it consists on the following: I need to have a containerized Database. When the load to the database goes up and the database gets overloaded, I need to pull up another container(pod) with the database. The problem is that the new pod needs to have some data preloaded (for reading purposes to the users) and when the load goes down, the new pod will get terminated and the data stored in there needs to be stored in a central database (to avoid loosing it).

I'm using a Kubernetes cluster (Google Kubernetes Engine) for the pods and Mongo db. It kind of looks like this

DB Diagram

I know that the problem described above is probably not the recommended approach, but that's what they are asking us to do.

Now, the problem is that MongoDB does not allow to do that (merge content from several databases into one database). A script that is controlling the pods (that need to be handled dinamically) and pulling the data from them and pushing it to the central database is complicated and things like having control of the data that was already pulled need to be taking care of.

My Idea of Solution

So, my idea was that all the containers point to the same volume. That means that the files in the directory '/data/db' (where mongo stores it files) of every pod are the same for all the pods because the same volume is mounted for all the pods. It kind of looks like this

Same Volume Mounted for each Pod

Kubernetes allows you to use several volumes. The ones that allow ReadWriteMany are NFS and Cephfs among others. I tried the example of this NFS link but it did not worked. The first pod started successfully but the others got stucked in "Starting Container". I assume that the volume could not be mounted for the other pods because the WriteMany was not allowed.

I tried creating a Cephfs cluster manually, but I am having some trouble to use the cluster from the Kubernetes Cluster. My Question is: will cephfs do the job? Can cephfs handle several writers in the same file? If it can, will the Mongo pods go up successfully? NFS was supposed to work, but it didn't.