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It is not always possible to exactly identify the CPU and RAM requirements at the time of deploying a VM. But for various reasons it may be required to scale up these resources later on. At that time there is no other way but to restart the VM with increased resources. Dynamic scaling for CPU and RAM feature would allow to change these resources for a running VM avoiding any downtime.

Currently CS allows updating CPU/RAM by changing to a different compute offering for stopped VMs. This feature will enable the same for running VMs.

Purpose

This document describes the specifications and design of the feature.

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• Ability to scale up CPU and/or RAM for running user VMs based on predefined compute offerings
• Ability to scale up CPU and/or RAM for running system VMs based on predefined system compute offerings
• If scaling up requires a migration it will be limited within the cluster only - if the current host where VM is running has capacity then simply the resources will be scaled up, if not live migration will be done within the cluster and then resources will be scaled up. If no suitable host is found operation will fail. In future if live migration across across clusters is possible then this constraint can be relaxed.
• Ability to mark the VM for scale up at creation time (see open issue#1)
• Ability to scale down CPU and RAM (see open issue#2)
• No check for guest OS compatibility (can be considered only if there is a concise document/API listing for supported guest OS's for each hypervisor)
• Only supported for newly created VMs, existing VMs (from prior CS releases) won't have the capability to scale up*- ability to scale up CPU and/or RAM for running system VMs based on predefined system compute offerings

Hypervisor support

- Currently planning to do it for Vmware. Support for other HVs can also be added based on HV capabilities.

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Allocation logic: Refer to flow chart below

Web Services APIs

list changes to existing web services APIs and new APIs introduced with signatures and throughout documentation

UI flow

• either demonstrate it visually here or link to relevant mockups

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Following APIs needs to be changed:

upgradeVirtualMachine - This is an existing API and take vm_id and compute_offering_id as inputs. This is a sync call currently and will be modified to async (breaking change but I feel should be fine). For system VMs the same API can be used but proper access checks would be done.

createServiceOffering - boolean flag indicating if dynamic scale up of CPU/RAM is allowed (see open issue# 1)

UI flow

TBD

Open Issues

1. Should VMs be always marked for dynamic scaling? If so should this be a VM property or part of compute offering? Should dynamic scaling be treated as premium service, in that case having it in compute offering makes more sense from usage/billing perspective?

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2. Should scale down be allowed? It can be explicitly prevented since none of the HVs/guest OS supports it.

3. There is also an option of having a custom compute offering where user can specify values for CPU

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and RAM during deployment or scaling up. But am not sure if this option can be misused

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since this is a user level API. Another complexity is to capture usage.

Test cases

TBD

Appendix

Appendix A:

Appendix B: