CPU and RAM Overcommit

Introduction:

This document describes the Cpu/Ram overcommit feature.

In the current implementation the cpu overcommit is global configuration value. This needs to be changed to provide a more granular control over the overcommit parameters. Currently there is no provision for ram overcommit.

This feature implements the ram overcommit and allows the ram and cpu overcommit ratios to be specified on a per cluster basis.

Use case:

change the vm density on all the hosts in a given cluster. This can be done by specifying the cpu and ram overcommit ratios.

Design description:

Admin can give the cpu and ram overcommit ratios at the time of creating a cluster or update the values after creating.

Cloudstack will deploy the vms based the overcommit ratios. If the overcommit ratio of a particular cluster is updated, only the vms deployed hereafter will be deployed based on the updated overcommit ratios.

supported Hypervisors.

XenServer
KVM
VMware

APIs:

AddCluster Will be modified to include the cpu and ram overcommit values in the cluster parameters.

UpdateOvercommitRatio Updates the overcommit ratios of a cluster.

*All the perameters are optional but of the two parameters in bold atleast one is required.
If value is not provided we default it to 1, meaning no overcommiting of resources by default.

DB changes:

Adding new colums to table cluster to store the cpu and ram overcommit ratios.

Upgrade scenario:

On upgrade the existing cluster tables will be upadated with above new columns.