Auto-scale Compute based on Consumption of Resources¶
As a user of OpenStack I want to define a logical group of compute resources which are increased or decreased automatically based on the consumption of discrete physical resources within my instances, for example CPU or Memory utilization; Disk IOPS, etc.
Problem description¶
In many ways, this is the basic use case for Auto-Scaling in OpenStack.
An OpenStack user, whether admin or operator, defines logic for triggering the auto-scaling based on the consumption of resources in the cloud. The resources could be CPU cycles, storage, memory, network, or a combination. The logic will typically define both scale up and scale down thresholds, and include an upper and lower bound for scaling. An orchestration engine for the cloud will be instructed to perform the scale up or scale down operations as specified.
This use case was called out in the Denver 2019 PTG - https://etherpad.openstack.org/p/DEN-auto-scaling-SIG
OpenStack projects used¶
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Inputs and decision-making¶
The resources monitoring used to determine auto scaling can be any monitored metric.
A few classic examples of metrics are:
Overall CPU percentage on a host of Virtual Machines
CPU percentabe utilization averaged across a group of Virtual Machines See https://github.com/sjamgade/monasca-autoscaling/blob/master/autoscaling.yaml for an example.
System memory average utilization percentage
Storage or disk space utilization percentage
In most cases, a high and a low threshold for the metric are determined to correspond with scale up or scale down actions.
Auto-scaling¶
Existing implementation(s)¶
Monasca and Heat
Monasca can monitor the physical resources and generate alarms if a resource usage exceeds a threshold. The alarm notification can then trigger a Heat template and scale the topology appropriately.
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