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Version: 1.2.0

Configuration V2

Introduction​

Over time the YuniKorn configuration has increased in complexity. The current configuration for YuniKorn is split over a number of different options, file and command line, and formats. There is a requirement now to define an overall configuration approach that can be used for all components.

Goals​

  • Define a configuration format
  • Define an update and modification strategy
  • Provide consistency between configuration of YuniKorn components
  • Legacy migration strategy

Non-Goals​

  • Redefine the queue configuration
  • Migration timeline for the old configuration options

References​

Implementation JIRA​

YUNIKORN-1221 - [Umbrella] Configuration V2

Other relevant JIRAs​

Services to cover​

  • Scheduler (Standard) - K8Shim + Core
  • Scheduler (Plugin) - K8Shim + Core
  • Admission controller

Services excluded​

Configuration format​

Currently only Kubernetes is a supported deployment pattern. Future shims may need an alternative configuration syntax. To enable this, we will update the scheduler interface to support passing the core configuration (the content of the queues.yaml ConfigMap entry) to the core on startup and refresh. The existing config watcher functionality in the core will be removed and the shim will gain the responsibility for watching for ConfigMap changes. The shim actually already has this ability now, it is just not used.

We will use two ConfigMaps to configure YuniKorn:

  • yunikorn-defaults
    • This will be a new ConfigMap written by Helm; it will contain only values explicitly configured by an administrator via Helm variables.
  • yunikorn-configs
    • This ConfigMap will contain overrides for yunikorn-defaults. It was previously a Helm hook in previous YuniKorn releases; it will no longer be managed by Helm and may be updated freely by third-party tools.

The effective configuration will be the combination of both yunikorn-defaults and yunikorn-configs, with yunikorn-configs taking precedence.

Neither ConfigMap (even the existing one) is required for proper functionality. In the case where a ConfigMap does not exist, we will use compiled-in defaults for all options. This enables bootstrapping in a variety of environments, including local development mode, as the ConfigMap need not exist to bring the scheduler components up. Future configuration options should be set via the ConfigMap exclusively.

Mutability of configuration values​

We should strive for hot-reload of all configuration values where possible. Where hot-reload is not implemented, this should be clearly documented. For the initial release, the core config and admission controller will be hot-reloadable but many items in the shim will likely not be. The shim was not designed to hot-reload anything so this will be a large future task. Some items may never be reloadable due to architectural limitations.

Update handling​

Given the security issues involved with updates, the default Kubernetes access control alone should be used for ConfigMap updates. We can still syntax-check the core side of the configuration in the admission controller as before. Partial updates are allowed as Kubernetes supports patching of ConfigMaps.

Legacy configuration handling​

Helm will be updated to render all existing legacy options into the yunikorn-defaults ConfigMap for easier transition to the new configuration format. Consequently, it is not necessary for YuniKorn components to parse the old environment and command-line arguments.

Environment variables​

All environment variables for all services will be removed, with the exception of:

  • NAMESPACE
    • Default value: default
    • Will be auto-populated from Helm and resolve to the pod's running namespace
    • Needed so that YuniKorn can determine what namespace it was launched in
    • Should only be provided explicitly at development time
  • KUBECONFIG
    • Default value: $HOME/.kube/config
    • Will be ignored if running inside Kubernetes; in-cluster configuration will be used in that case
    • Needed so that we can bootstrap to K8s and load the YuniKorn ConfigMap at runtime
    • Should only be provided explicitly at development time

Helm considerations​

All configuration options which have moved into the ConfigMap will be marked as deprecated in the Helm chart documentation. Their replacement is the more generic yunikornDefaults dictionary. If the legacy values are present but the associated yunikornDefaults entry is missing, the legacy configuration value will be used. This will allow users some time to migrate to the new configuration style. The legacy attributes will be removed in a future release.

Core Configuration​

The core scheduler configuration is loaded from the queues.yaml section of the ConfigMap, assuming service.policyGroup is set to the default value queues. If the policy group has been customized, core scheduler configuration will be read from {service.policyGroup}.yaml. This section is special as its contents are passed directly to the core for evaluation and update and is not read directly by the shim. The content of this section is unchanged from prior releases.

Appendix​

Default ConfigMap​

If not present, the default ConfigMap will resolve to these defaults. Additionally, individual options will resolve to those listed here if not specified. Note that these values are subject to change in future releases.

apiVersion: v1 kind: ConfigMap metadata: name: yunikorn-configs data: service.clusterId: "mycluster" service.policyGroup: "queues" service.schedulingInterval: "1s" service.volumeBindTimeout: "10s" service.eventChannelCapacity: "1048576" service.dispatchTimeout: "5m" service.operatorPlugins: "general" service.disableGangScheduling: "false" service.enableConfigHotRefresh: "true" service.placeholderImage: "registry.k8s.io/pause:3.7" health.checkInterval: "30s" log.level: "0" kubernetes.qps: "1000" kubernetes.burst: "1000" admissionController.webHook.amServiceName: "yunikorn-admission-controller-service" admissionController.webHook.schedulerServiceAddress: "yunikorn-service:9080" admissionController.filtering.processNamespaces: "" admissionController.filtering.bypassNamespaces: "^kube-system$" admissionController.filtering.labelNamespaces: "" admissionController.filtering.noLabelNamespaces: "" admissionController.accessControl.bypassAuth: "false" admissionController.accessControl.trustControllers: "true" admissionController.accessControl.systemUsers: "^system:serviceaccount:kube-system:" admissionController.accessControl.externalUsers: "" admissionController.accessControl.externalGroups: "" queues.yaml: | partitions:

  • name: default placementrules:
    • name: tag value: namespace create: true queues:
    • name: root submitacl: '*'`

Admission Controller Configuration​

Removed Environment Variables​

  • POLICY_GROUP
    • Use ConfigMap: service.policyGroup
  • ENABLE_CONFIG_HOT_REFRESH
    • Use ConfigMap: service.enableConfigHotRefresh
  • SCHEDULER_SERVICE_ADDRESS
    • Use ConfigMap: admissionController.webHook.schedulerServiceAddress
  • ADMISSION_CONTROLLER_SERVICE
    • Use ConfigMap: admissionController.webHook.amServiceName
  • ADMISSION_CONTROLLER_NAMESPACE
    • Use Environment variable: NAMESPACE
  • ADMISSION_CONTROLLER_PROCESS_NAMESPACES
    • Use ConfigMap: admissionController.filtering.processNamespaces
  • ADMISSION_CONTROLLER_BYPASS_NAMESPACES
    • Use ConfigMap: admissionController.filtering.bypassNamespaces
  • ADMISSON_CONTROLLER_LABEL_NAMESPACES
    • Use ConfigMap: admissionController.filtering.labelNamespaces
  • ADMISSION_CONTROLLER_NO_LABEL_NAMESPACES
    • Use ConfigMap: admissionController.filtering.noLabelNamespaces

Removed CLI Options​

None

Scheduler (Standard) Configuration​

Removed Environment Variables​

  • USER_LABEL_KEY
    • No replacement
  • OPERATOR_PLUGINS
    • Use ConfigMap: service.operatorPlugins
  • PLACEHOLDER_IMAGE
    • Use ConfigMap: service.placeholderImage

Removed CLI Options​

  • -clusterId
    • Use ConfigMap: service.clusterId
  • -clusterVersion
    • No replacement
  • -policyGroup
    • Use ConfigMap: service.policyGroup
  • -interval
    • Use ConfigMap: service.schedulingInterval
  • -logLevel
    • Use ConfigMap: log.level
  • -logEncoding
    • No replacement
  • -logFile
    • No replacement
  • -volumeBindTimeout
    • Use ConfigMap: service.volumeBindTimeout
  • -eventChannelCapacity
    • Use ConfigMap: service.eventChannelCapacity
  • -dispatchTimeout
    • Use ConfigMap: service.dispatchTimeout
  • -kubeQPS
    • Use ConfigMap: kubernetes.qps
  • -kubeBurst
    • Use ConfigMap: kubernetes.burst
  • -operatorPlugins
    • Use ConfigMap: service.operatorPlugins
  • -enableConfigHotRefresh
    • Use ConfigMap: service.enableConfigHotRefresh
  • -disableGangScheduling
    • Use ConfigMap: service.disableGangScheduling
  • -userLabelKey
    • No replacement
  • -placeHolderImage Use ConfigMap: service.placeholderImage

Scheduler (Plugin) Configuration​

Removed Environment Variables​

  • USER_LABEL_KEY
    • No replacement
  • OPERATOR_PLUGINS
    • Use ConfigMap: service.operatorPlugins
  • PLACEHOLDER_IMAGE
    • Use ConfigMap: service.placeholderImage

Removed CLI Options​

  • --yk-scheduler-name
    • No replacement
  • --yk-cluster-id
    • Use ConfigMap: service.clusterId
  • --yk-cluster-version
    • No replacement
  • --yk-policy-group
    • Use ConfigMap: service.policyGroup
  • `--yk-scheduling-interval
    • Use ConfigMap: service.schedulingInterval
  • --yk-kube-config
    • Use environment: KUBECONFIG
  • --yk-log-level
    • Use ConfigMap: log.level
  • --yk-log-encoding
    • No replacement
  • --yk-log-file
    • No replacement
  • --yk-event-channel-capacity
    • Use ConfigMap: service.eventChannelCapacity
  • --yk-dispatcher-timeout
    • Use ConfigMap: service.dispatchTimeout
  • --yk-kube-qps
    • Use ConfigMap: kubernetes.qps
  • --yk-kube-burst
    • Use ConfigMap: kubernetes.burst
  • --yk-operator-plugins
    • Use ConfigMap: service.operatorPlugins
  • --yk-enable-config-hot-refresh
    • Use ConfigMap: service.enableConfigHotRefresh
  • --yk-disable-gang-scheduling
    • Use ConfigMap: service.disableGangScheduling
  • --yk-user-label-key
    • No replacement
  • --yk-placeholder-image
    • Use ConfigMap: service.placeholderImage

Helm Configuration​

Removed Options​

  • userLabelKey
    • No replacement

Deprecated Options​

  • operatorPlugins
    • Use ConfigMap: service.operatorPlugins
  • placeHolderImage
    • Use ConfigMap: service.placeholderImage
  • admissionController.processNamespaces
    • Use ConfigMap: admissionController.filtering.processNamespaces
  • admissionController.bypassNamespaces
    • Use ConfigMap: admissionController.filtering.bypassNamespaces
  • admissionController.labelNamespaces
    • Use ConfigMap: admissionController.filtering.labelNamespaces
  • admissionController.noLabelNamespaces
    • Use ConfigMap: admissionController.filtering.noLabelNamespaces
  • configuration
    • Use ConfigMap: queues.yaml