HPA support design

hpa-support-design.md

HPA design

Feature/enhancement description

Support to Configure HorizontalPodAutoscaler in Rancher UI. And Support to configure HPA rules for deployment when we creating them.

Requirements

API and object model changes

TypeMeta

APIGroup	autoscaling
Version	v2beta2
Kind	HorizontalPodAutoscaler

There are 3 versions for HorizontalPodAutoscaler.

• v1 - only support cpu average for scaling metric. Since k8s 1.1
• v2beta1 - support multiple metric type including cpu, memory and custom metrics. Only value and average value of target metric are supported. Since k8s 1.6
• v2beta2 - Including v2beta1 and support Utilization metric type. Since k8s 1.12

So the best api verison for the HPA object is v2beta1

Rancher API Schema for HPA

HorizontalPodAutoscaler:

Name	Type	Create	Update	Null	Required	Remark
id	dnsLabel
name	string	*	*	*		(set id if null)
namespaceId	dnsLabel
description	string	*	*	*		annotation field
workloadId	dnsLabel	*	*		*	workloadId will be translated into CrossVersionObjectReference
minReplicas	int	*	*	*
maxReplicas	int	*	*		*
metrics	array[metricSpec]	*	*	*
observedGeneration	int64					from embed status field
lastScaleTime	time					from embed status field
currentReplicas	int32					from embed status field
desiredReplicas	int32					from embed status field
currentMetrics	array[metricStatus]					from embed status field
conditions	array[condition]					from embed status field, ScalingActive/AbleToScale/ScalingLimited

MetricSpec:

Name	Type	Create	Update	Null	Required	Remark
type	enum					Object,Pods,Resource,External
name	dnsLabel					use for type Object, Pods and External
selector	labelSelector					use for type Object, Pods and External
describedObject	crossVersionObjectReference					use for type Object
metricType	enum					metrics quantity type, value, averageValue and averageUtilization, if value or averageValue is set, the value should be in quantity format. If averageUtilization is set, value should be in number format
value	string					value for the metric
resourceName	enum					cpu, memory, storage and ephemeral-storage only used when type is Resource

MetricStatus:

Name	Type	Create	Update	Null	Required	Remark
type	enum					Object,Pods,Resource,External
name	dnsLabel					use for type Object, Pods and External
selector	labelSelector					use for type Object, Pods and External
describedObject	crossVersionObjectReference					use for type Object
metricType	enum					metrics quantity type, value, averageValue and averageUtilization
value	quantity					current value for the metric
resourceName	enum					cpu, memory, storage and ephemeral-storage only used when type is Resource

New field for deployment/replicaController for autoscaling.

Name	Type	Create	Update	Null	Required	Remark
scaling	scaling	*	*	*		annotation field of deployment and replicaController

Scaling:

One scaling object will repect to one HPA object with several metrics in it.

Name	Type	Create	Update	Null	Required	Remark
minReplicas	int	*	*	*
maxReplicas	int	*	*		*
metrics	array[scalingMetric]	*	*	*

ScalingMetric:

Name	Type	Create	Update	Null	Required	Remark
name	string					only support cpu,memory
valueType	enum					only support averageUtilization, averageValue
value	quantity					the value to trigger scaling

Custom API logic

For HorizontalPodAutoscaler

• Embed spec and status
• Add description for resource object

For HorizontalPodAutoscalerSpec

• Transform workloadId to scaleTargetRef. And only deployment and replicaController should be allowed to be set.

For MetricSpec

• Embed objectMetricSource, podsMetricSource, resourceMetricSource and externalMetricStatus. Create new mapper to assign different value with different type.

For MetricStatus

• Embed objectMetricStatus, podsMetricStatus, resourceMetricStatus and externalMetricStatus. Create new mapper to assign different value with different type.

Business logic changes

Adding new logic for workload.

• Add new controllers for deployment and replicaController to handle the new autoscaling field.

RBAC

HorizontalPodAutoscaler is a namespaced resource. It has the same RBAC rules as other namespaced resources.

Other important design or architecture changes

Testing

Three aspect should be test when adding HPA object

• For the deployment and replicaController, we should test the new annotation field. Each scaling should create a HPA object accordingly.
• For the HPA resource, It should test the API translation from Rancher API to Kubernetes object is ok or not.
• For the HPA, we should test the rules we set for scaling will work as expected.

Changelog

Review action items and notes