druid/docs/development/extensions-contrib/k8s-jobs.md

id	title
k8s-jobs	MM-less Druid in K8s

Apache Druid Extension to enable using Kubernetes for launching and managing tasks instead of the Middle Managers. This extension allows you to launch tasks as kubernetes jobs removing the need for your middle manager.

Consider this an EXPERIMENTAL feature mostly because it has not been tested yet on a wide variety of long-running Druid clusters.

How it works

The K8s extension builds a pod spec using the specified pod adapter, the default implementation takes the podSpec of your Overlord pod and creates a kubernetes job from this podSpec. Thus if you have sidecars such as Splunk or Istio it can optionally launch a task as a K8s job. All jobs are natively restorable, they are decoupled from the druid deployment, thus restarting pods or doing upgrades has no affect on tasks in flight. They will continue to run and when the overlord comes back up it will start tracking them again.

Pod Adapters

The logic defining how the pod template is built for your kubernetes job depends on which pod adapter you have specified.

Overlord Single Container Pod Adapter

The overlord single container pod adapter takes the podSpec of your Overlord pod and creates a kubernetes job from this podSpec. This is the default pod adapter implementation, to explicitly enable it you can specify the runtime property druid.indexer.runner.k8s.adapter.type: overlordSingleContainer

Overlord Multi Container Pod Adapter

The overlord multi container pod adapter takes the podSpec of your Overlord pod and creates a kubernetes job from this podSpec. It uses kubexit to manage dependency ordering between the main container that runs your druid peon and other sidecars defined in the Overlord pod spec. To enable this pod adapter you can specify the runtime property druid.indexer.runner.k8s.adapter.type: overlordMultiContainer

Custom Template Pod Adapter

The custom template pod adapter allows you to specify a pod template file per task type. This adapter requires you to specify a base pod spec which will be used in the case that a task specific pod spec has not been defined. To enable this pod adapter you can specify the runtime property druid.indexer.runner.k8s.adapter.type: customTemplateAdapter

The base pod template must be specified as the runtime property druid.indexer.runner.k8s.podTemplate.base: /path/to/basePodSpec.yaml Task specific pod templates must be specified as the runtime property druid.indexer.runner.k8s.podTemplate.{taskType}: /path/to/taskSpecificPodSpec.yaml where {taskType} is the name of the task type i.e index_parallel

Configuration

To use this extension please make sure to includedruid-kubernetes-overlord-extensions in the extensions load list for your overlord process.

The extension uses the task queue to limit how many concurrent tasks (K8s jobs) are in flight so it is required you have a reasonable value for druid.indexer.queue.maxSize. Additionally set the variable druid.indexer.runner.namespace to the namespace in which you are running druid.

Other configurations required are: druid.indexer.runner.type: k8s and druid.indexer.task.encapsulatedTask: true

You can add optional labels to your K8s jobs / pods if you need them by using the following configuration: druid.indexer.runner.labels: '{"key":"value"}' Annotations are the same with: druid.indexer.runner.annotations: '{"key":"value"}'

All other configurations you had for the middle manager tasks must be moved under the overlord with one caveat, you must specify javaOpts as an array: druid.indexer.runner.javaOptsArray, druid.indexer.runner.javaOpts is no longer supported.

If you are running without a middle manager you need to also use druid.processing.intermediaryData.storage.type=deepstore

Additional Configuration

Properties

Property	Possible Values	Description	Default	required
druid.indexer.runner.debugJobs	boolean	Clean up K8s jobs after tasks complete.	False	No
druid.indexer.runner.sidecarSupport	boolean	Deprecated, specify adapter type as runtime property druid.indexer.runner.k8s.adapter.type: overlordMultiContainer instead. If your overlord pod has sidecars, this will attempt to start the task with the same sidecars as the overlord pod.	False	No
druid.indexer.runner.primaryContainerName	String	If running with sidecars, the primaryContainerName should be that of your druid container like druid-overlord.	First container in podSpec list	No
druid.indexer.runner.kubexitImage	String	Used kubexit project to help shutdown sidecars when the main pod completes. Otherwise jobs with sidecars never terminate.	karlkfi/kubexit:latest	No
druid.indexer.runner.disableClientProxy	boolean	Use this if you have a global http(s) proxy and you wish to bypass it.	false	No
druid.indexer.runner.maxTaskDuration	Duration	Max time a task is allowed to run for before getting killed	PT4H	No
druid.indexer.runner.taskCleanupDelay	Duration	How long do jobs stay around before getting reaped from K8s	P2D	No
druid.indexer.runner.taskCleanupInterval	Duration	How often to check for jobs to be reaped	PT10M	No
druid.indexer.runner.K8sjobLaunchTimeout	Duration	How long to wait to launch a K8s task before marking it as failed, on a resource constrained cluster it may take some time.	PT1H	No
druid.indexer.runner.javaOptsArray	JsonArray	java opts for the task.	-Xmx1g	No
druid.indexer.runner.labels	JsonObject	Additional labels you want to add to peon pod	{}	No
druid.indexer.runner.annotations	JsonObject	Additional annotations you want to add to peon pod	{}	No
druid.indexer.runner.peonMonitors	JsonArray	Overrides druid.monitoring.monitors. Use this property if you don't want to inherit monitors from the Overlord.	[]	No
druid.indexer.runner.graceTerminationPeriodSeconds	Long	Number of seconds you want to wait after a sigterm for container lifecycle hooks to complete. Keep at a smaller value if you want tasks to hold locks for shorter periods.	PT30S (K8s default)	No

Gotchas

• You must have in your role the ability to launch jobs.
• All Druid Pods belonging to one Druid cluster must be inside same kubernetes namespace.
• For the sidecar support to work, your entry point / command in docker must be explicitly defined your spec.

You can't have something like this: Dockerfile: ENTRYPOINT: ["foo.sh"]

and in your sidecar specs:

        name: foo
        args: 
           - arg1
           - arg2 

That will not work, because we cannot decipher what your command is, the extension needs to know it explicitly. *Even for sidecars like Istio which are dynamically created by the service mesh, this needs to happen.

Instead do the following: You can keep your Dockerfile the same but you must have a sidecar spec like so:

        name: foo
        command: foo.sh
        args: 
           - arg1
           - arg2 

The following roles must also be accessible. An example spec could be:

apiVersion: rbac.authorization.k8s.io/v1
kind: Role
metadata:
  name: druid-cluster
rules:
- apiGroups:
  - ""
  resources:
  - pods
  - configmaps
  - jobs
  verbs:
  - '*'
---
kind: RoleBinding
apiVersion: rbac.authorization.k8s.io/v1
metadata:
  name: druid-cluster
subjects:
- kind: ServiceAccount
  name: default
roleRef:
  kind: Role
  name: druid-cluster
  apiGroup: rbac.authorization.k8s.io