Project: MongoDB configure cacheSizeGB based on memory requests/limits

[runningman84]

According to the docs the cacheSizeGB should be based on the resource limits of the container:
```
If you run mongod in a container (e.g. lxc, cgroups, Docker, etc.) that does not have access to all of the RAM available in a system, you must set storage.wiredTiger.engineConfig.cacheSizeGB to a value less than the amount of RAM available in the container. The exact amount depends on the other processes running in the container.
````
https://docs.mongodb.com/manual/reference/configuration-options/

Right now if you run mongodb instances using kubedb in a "shared" kubernetes cluser, multiple containers take about 50% of the available memory of the system for cache. This will lead to container crashes or oom problems.

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[runningman84]

this is my current workaround
https://github.com/arvatoaws/graylog-helm-chart/blob/master/graylog/templates/mongodb-config.yaml