Apache YuniKorn - A Universal Scheduler

Apache YuniKorn is a light-weight, universal resource scheduler for container orchestrator systems. It was created to achieve fine-grained resource sharing for various workloads efficiently on a large scale, multi-tenant, and cloud-native environment. YuniKorn brings a unified, cross-platform, scheduling experience for mixed workloads that consist of stateless batch workloads and stateful services.

YuniKorn now supports K8s and can be deployed as a custom K8s scheduler. YuniKorn's architecture design also allows adding different shim layer and adopt to different ResourceManager implementation including Apache Hadoop YARN, or any other systems.

Feature highlights

Features to support both batch jobs and long-running/stateful services.
Hierarchy queues with min/max resource quotas.
Resource fairness between queues, users and apps.
Cross-queue preemption based on fairness.
Automatically map incoming container requests to queues by policies.
Node partition: partition cluster to sub-clusters with dedicated quota/ACL management.
Fully compatible with K8s predicates, events, PV/PVC and admin commands.
Supports to work with Cluster AutoScaler to drive cluster scales up and down.

Deployment model

YuniKorn can be deployed with helm-charts on an existing K8s cluster. It can be deployed with or without the admission controller. When the admission controller is enabled, YuniKorn will be the primary scheduler that takes over the resource scheduling (the admission controller runs a mutation webhook that automatically mutates pod spec's schedulerName to yunikorn); when it is disabled, user needs to manually change the schedulerName to yunikorn in order to get apps scheduled by YuniKorn.

Supported K8s versions

K8s Version	Support?
1.20.x (or earlier)	X
1.21.x	√
1.22.x	√
1.23.x	√
1.24.x	√
1.25.x	√
1.26.x	√

Installing the chart

helm repo add yunikorn  https://apache.github.io/yunikorn-release
helm repo update 
helm install yunikorn yunikorn/yunikorn

Configuration

The following table lists the configurable parameters of the YuniKorn chart and their default values:

Parameter	Description	Default
`imagePullSecrets`	Docker repository secrets	`[]`
`replicaCount`	Scheduler replicas to be deployed	`1`
`serviceAccount`	Service account name	`yunikorn-admin`
`hostNetwork`	Whether scheduler should run in the host network	`false`
`image.repository`	Scheduler image repository	`apache/yunikorn`
`image.tag`	Scheduler image tag	`scheduler-latest`
`image.pullPolicy`	Scheduler image pull policy	`Always`
`pluginImage.repository`	Scheduler plugin image repository	`apache/yunikorn`
`pluginImage.tag`	Scheduler plugin image tag	`scheduler-plugin-latest`
`pluginImage.pullPolicy`	Scheduler plugin image pull policy	`Always`
`podLabels`	Scheduler pod labels	`{}`
`admissionController.podLabels`	Admission controller pod labels	`{}`
`admissionController.replicaCount`	Admission controller replicas to be deployed	`1`
`admissionController.serviceAccount`	Admission controller service account name	`yunikorn-admission-controller`
`admissionController.image.repository`	Admission controller image repository	`apache/yunikorn`
`admissionController.image.tag`	Admission controller image tag	`admission-latest`
`admissionController.image.pullPolicy`	Admission controller image pull policy	`Always`
`admissionController.hostNetwork`	Whether admission controller should run in the host network	`true`
`admissionController.resources.requests.cpu`	Admission controller CPU resource requests	`100m`
`admissionController.resources.requests.memory`	Admission controller memory resource requests	`500Mi`
`admissionController.resources.limits.cpu`	Admission controller CPU resource limit	`500m`
`admissionController.resources.limits.memory`	Admission controller memory resource limit	`500Mi`
`admissionController.nodeSelector`	Admission controller deployment nodeSelector(s)	`{}`
`admissionController.tolerations`	Admission controller deployment tolerations	`[]`
`admissionController.affinity`	Admission controller deployment affinity	`{}`
`admissionController.service.type`	Admission controller service type	`ClusterIP`
`admissionController.priorityClassName`	Admission controller pod priority	`""`
`priorityClassName`	Scheduler pod priority	`""`
`service.type`	Scheduler service type	`ClusterIP`
`service.port`	Port of the scheduler service	`9080`
`service.portWeb`	Port of the web application service	`9889`
`resources.requests.cpu`	CPU resource requests	`200m`
`resources.requests.memory`	Memory resource requests	`1Gi`
`resources.limits.cpu`	CPU resource limit	`4`
`resources.limits.memory`	Memory resource limit	`2Gi`
`web.image.repository`	Web app image repository	`apache/yunikorn`
`web.image.tag`	Web app image tag	`web-latest`
`web.image.pullPolicy`	Web app image pull policy	`Always`
`web.resources.requests.cpu`	Web app CPU resource requests	`100m`
`web.resources.requests.memory`	Web app memory resource requests	`100Mi`
`web.resources.limits.cpu`	Web app CPU resource limit	`200m`
`web.resources.limits.memory`	Web app memory resource limit	`500Mi`
`embedAdmissionController`	Flag for enabling/disabling the admission controller	`true`
`enableSchedulerPlugin`	Flag for enabling/disabling scheduler plugin mode	`false`
`nodeSelector`	Scheduler deployment nodeSelector(s)	`{}`
`tolerations`	Scheduler deployment tolerations	`[]`
`affinity`	Scheduler deployment affinity	`{}`
`yunikornDefaults`	Data for the `yunikorn-defaults` ConfigMap	`{}`

These parameters can be passed in via helm's --set and --values (-f) options, such as --set resources.requests.cpu=2000m or -f myvalues.yaml.

In addition to these parameters, YuniKorn supports reading most of its runtime configuration directly from two ConfigMaps in the installed namespace: yunikorn-defaults and yunikorn-configs. The yunikorn-defaults ConfigMap is rendered by Helm based on the contents of the yunikornDefaults parameter. The yunikorn-configs ConfigMap is entirely ignored by Helm, and can be populated (or not) using external mechanisms. At runtime, YuniKorn will evaluate both ConfigMaps, using the contents of yunikorn-configs as an override to yunikorn-defaults.

Deprecated Configuration

The following configuration parameters are deprecated and will be ignored in a future release of YuniKorn:

Parameter	Description	Replacement
`operatorPlugins`	Scheduler operator plugins	`service.operatorPlugins` ConfigMap entry
`placeholderImage`	Docker image of the placeholder pods	`service.placeholderImage` ConfigMap entry
`admissionController.processNamespaces`	List of namespace regexes to process (empty=ALL)	`admissionController.filtering.processNamespaces` ConfigMap entry
`admissionController.bypassNamespaces`	List of namespace regexes to bypass (empty=NONE)	`admissionController.filtering.bypassNamespaces` ConfigMap entry
`admissionController.labelNamespaces`	List of namespace regexes to label (empty=ALL)	`admissionController.filtering.labelNamespaces` ConfigMap entry
`admissionController.noLabelNamespaces`	List of namespace regexes not to label (empty=NONE)	`admissionController.filtering.noLabelNamespaces` ConfigMap entry
`configuration`	YAML-formatted queue configuration	`queues.yaml` ConfigMap entry

Currently, if both the deprecated parameter and the replacement ConfigMap entry are specified, the ConfigMap entry will take precedence.