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 for each task using the specified pod adapter. 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.

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 druid.indexer.runner.capacity to limit the number of k8s jobs in flight. A good initial value for this would be the sum of the total task slots of all the middle managers you were running before switching to K8s based ingestion. The K8s task runner uses one thread per Job that is created, so setting this number too large can cause memory issues on the overlord. 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

Dynamic config

Druid operators can dynamically tune certain features within this extension. You don't need to restart the Overlord service for these changes to take effect.

Druid can dynamically tune pod template selection, which allows you to configure the pod template based on the task to be run. To enable dynamic pod template selection, first configure the custom template pod adapter.

Use the following APIs to view and update the dynamic configuration for the Kubernetes task runner.

To use these APIs, ensure you have read and write permissions for the CONFIG resource type with the resource name "CONFIG". For more information on permissions, see User authentication and authorization.

Get dynamic configuration

Retrieves the current dynamic execution config for the Kubernetes task runner. Returns a JSON object with the dynamic configuration properties.

URL

GET /druid/indexer/v1/k8s/taskrunner/executionconfig

Responses

Successfully retrieved dynamic configuration

Sample request

curl "http://ROUTER_IP:ROUTER_PORT/druid/indexer/v1/k8s/taskrunner/executionconfig"

GET /druid/indexer/v1/k8s/taskrunner/executionconfig HTTP/1.1
Host: http://ROUTER_IP:ROUTER_PORT

Sample response

View the response

{
  "type": "default",
  "podTemplateSelectStrategy":
  {
    "type": "selectorBased",
    "selectors": [
      {
        "selectionKey": "podSpec1",
        "context.tags": {
          "userProvidedTag": ["tag1", "tag2"]
        },
        "dataSource": ["wikipedia"]
      },
      {
        "selectionKey": "podSpec2",
        "type": ["index_kafka"]
      }
    ]
  }
}

Update dynamic configuration

Updates the dynamic configuration for the Kubernetes Task Runner

URL

POST /druid/indexer/v1/k8s/taskrunner/executionconfig

Header parameters

The endpoint supports the following optional header parameters to populate the author and comment fields in the configuration history.

X-Druid-Author
- Type: String
- Author of the configuration change.
X-Druid-Comment
- Type: String
- Description for the update.

Responses

Successfully updated dynamic configuration

Sample request

curl "http://ROUTER_IP:ROUTER_PORT/druid/indexer/v1/k8s/taskrunner/executionconfig" \
--header 'Content-Type: application/json' \
--data '{
  "type": "default",
  "podTemplateSelectStrategy":
  {
    "type": "selectorBased",
    "selectors": [
      {
        "selectionKey": "podSpec1",
        "context.tags":
        {
          "userProvidedTag": ["tag1", "tag2"]
        },
        "dataSource": ["wikipedia"]
      },
      {
        "selectionKey": "podSpec2",
        "type": ["index_kafka"]
      }
    ]
  }
}'

POST /druid/indexer/v1/k8s/taskrunner/executionconfig HTTP/1.1
Host: http://ROUTER_IP:ROUTER_PORT
Content-Type: application/json

{
  "type": "default",
  "podTemplateSelectStrategy":
  {
    "type": "selectorBased",
    "selectors": [
      {
        "selectionKey": "podSpec1",
        "context.tags":
        {
          "userProvidedTag": ["tag1", "tag2"]
        },
        "dataSource": ["wikipedia"]
      },
      {
        "selectionKey": "podSpec2",
        "type": ["index_kafka"]
      }
    ]
  }
}

Sample response

A successful request returns an HTTP 200 OK message code and an empty response body.

Get dynamic configuration history

Retrieves the history of changes to Kubernetes task runner's dynamic execution config over an interval of time. Returns an empty array if there are no history records available.

URL

GET /druid/indexer/v1/k8s/taskrunner/executionconfig/history

Query parameters

The endpoint supports the following optional query parameters to filter results.

interval
- Type: String
- Limit the results to the specified time interval in ISO 8601 format delimited with /. For example, 2023-07-13/2023-07-19. The default interval is one week. You can change this period by setting druid.audit.manager.auditHistoryMillis in the runtime.properties file for the Coordinator.
count
- Type: Integer
- Limit the number of results to the last n entries.

Responses

Successfully retrieved dynamic configuration

Sample request

curl "http://ROUTER_IP:ROUTER_PORT/druid/indexer/v1/k8s/taskrunner/executionconfig/history"

GET /druid/indexer/v1/k8s/taskrunner/executionconfig/history HTTP/1.1
Host: http://ROUTER_IP:ROUTER_PORT

Sample response

View the response

[
  {
    "key": "k8s.taskrunner.config",
    "type": "k8s.taskrunner.config",
    "auditInfo": {
      "author": "",
      "comment": "",
      "ip": "127.0.0.1"
    },
    "payload": "{\"type\": \"default\",\"podTemplateSelectStrategy\":{\"type\": \"taskType\"}",
    "auditTime": "2024-06-13T20:59:51.622Z"
  }
]

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/Overlord Multi 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

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. Thus if you have sidecars such as Splunk or Istio it will be able to handle them. To enable this pod adapter you can specify the runtime property druid.indexer.runner.k8s.adapter.type: overlordMultiContainer

For the sidecar support to work for the multi container pod adapter, 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 

For both of these adapters, 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

Custom Template Pod Adapter

The custom template pod adapter allows you to specify a pod template file per task type for more flexibility on how to define your pods. This adapter expects a Pod Template to be available on the overlord's file system. This pod template is used as the base of the pod spec for the Kubernetes Job. You can override things like labels, environment variables, resources, annotation, or even the base image with this template. 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

Example Pod Template that uses the regular druid docker image

apiVersion: "v1"
kind: "PodTemplate"
template:
  metadata:
    annotations:
      sidecar.istio.io/proxyCPU: "512m" # to handle a injected istio sidecar
    labels:
      app.kubernetes.io/name: "druid-realtime-backend"
  spec:
    affinity: {}
    containers:
    - command:
        - sh
        - -c
        - |
          /peon.sh /druid/data 1
      env:
      - name: CUSTOM_ENV_VARIABLE
        value: "hello"
      image: apache/druid:31.0.0
      name: main
      ports:
      - containerPort: 8091
        name: druid-tls-port
        protocol: TCP
      - containerPort: 8100
        name: druid-port
        protocol: TCP
      resources:
        limits:
          cpu: "1"
          memory: 2400M
        requests:
          cpu: "1"
          memory: 2400M
      volumeMounts:
      - mountPath: /opt/druid/conf/druid/cluster/master/coordinator-overlord # runtime props are still mounted in this location because that's where peon.sh looks for configs
        name: nodetype-config-volume
        readOnly: true
      - mountPath: /druid/data
        name: data-volume
      - mountPath: /druid/deepstorage
        name: deepstorage-volume
    restartPolicy: "Never"
    securityContext:
      fsGroup: 1000
      runAsGroup: 1000
      runAsUser: 1000
    tolerations:
    - effect: NoExecute
      key: node.kubernetes.io/not-ready
      operator: Exists
      tolerationSeconds: 300
    - effect: NoExecute
      key: node.kubernetes.io/unreachable
      operator: Exists
      tolerationSeconds: 300
    volumes:
    - configMap:
        defaultMode: 420
        name: druid-tiny-cluster-peons-config
      name: nodetype-config-volume
    - emptyDir: {}
      name: data-volume
    - emptyDir: {}
      name: deepstorage-volume

The below runtime properties need to be passed to the Job's peon process.

druid.port=8100 (what port the peon should run on)
druid.peon.mode=remote
druid.service=druid/peon (for metrics reporting)
druid.indexer.task.baseTaskDir=/druid/data (this should match the argument to the ./peon.sh run command in the PodTemplate)
druid.indexer.runner.type=k8s
druid.indexer.task.encapsulatedTask=true

Any runtime property or JVM config used by the peon process can also be passed. E.G. below is a example of a ConfigMap that can be used to generate the nodetype-config-volume mount in the above template.

Example ConfigMap

kind: ConfigMap
metadata:
    name: druid-tiny-cluster-peons-config
    namespace: default
apiVersion: v1
data:
    jvm.config: |-
        -server
        -XX:MaxDirectMemorySize=1000M
        -Duser.timezone=UTC
        -Dfile.encoding=UTF-8
        -Dlog4j.debug
        -Djava.util.logging.manager=org.apache.logging.log4j.jul.LogManager
        -Djava.io.tmpdir=/druid/data
        -Xmx1024M
        -Xms1024M
    log4j2.xml: |-
        <?xml version="1.0" encoding="UTF-8" ?>
        <Configuration status="WARN">
            <Appenders>
                <Console name="Console" target="SYSTEM_OUT">
                    <PatternLayout pattern="%d{ISO8601} %p [%t] %c - %m%n"/>
                </Console>
            </Appenders>
            <Loggers>
                <Root level="info">
                    <AppenderRef ref="Console"/>
                </Root>
            </Loggers>
        </Configuration>
    runtime.properties: |
        druid.port=8100
        druid.service=druid/peon
        druid.server.http.numThreads=5
        druid.indexer.task.baseTaskDir=/druid/data
        druid.indexer.runner.type=k8s
        druid.peon.mode=remote
        druid.indexer.task.encapsulatedTask=true

Pod template selection

The pod template adapter can select which pod template should be used for a task using the task runner execution config

Select based on task type

The TaskTypePodTemplateSelectStrategy strategy selects pod templates based on task type for execution purposes, implementing the behavior that maps templates to specific task types. This is the default pod template selection strategy. To explicitly select this strategy, set the podTemplateSelectStrategy in the dynamic execution config to

{ "type": "default" }

Task specific pod templates can 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. For example, index_parallel.

If you are trying to use the default image's environment variable parsing feature to set runtime properties, you need to add a extra escape underscore when specifying pod templates. For example, set the environment variable druid_indexer_runner_k8s_podTemplate_index__kafka when you set the runtime property druid.indexer.runner.k8s.podTemplate.index_kafka

The following example shows a configuration for task-based pod template selection:

druid.indexer.runner.k8s.podTemplate.base=/path/to/basePodSpec.yaml
druid.indexer.runner.k8s.podTemplate.index_kafka=/path/to/kafkaPodSpec.yaml

Select based on one or more conditions

The SelectorBasedPodTemplateSelectStrategy strategy evaluates a series of criteria within selectors to determine which pod template to use to run the task. Pod templates are configured in the runtime properties like druid.indexer.runner.k8s.podTemplate.<selectionKey>=....

{
  "type": "selectorBased",
  "selectors": [
    {
      "selectionKey": "podSpec1", 
      "context.tags":
      {
        "userProvidedTag": ["tag1", "tag2"]
      },
      "dataSource": ["wikipedia"]
    },
    {
      "selectionKey": "podSpec2",
      "type": ["index_kafka"]
    }
  ]
}

Selectors are processed in order. Druid selects the template based on the first matching selector. If a task does not match any selector in the list, it will use the base pod template.

For a task to match a selector, all the conditions within the selector must match. A selector can match on

type: Type of the task
dataSource: Destination datasource of the task.
context.tags: Tags passed in the task's context.

Example

Set the following runtime properties to define the pod specs that can be used by Druid.

druid.indexer.runner.k8s.podTemplate.base=/path/to/basePodSpec.yaml
druid.indexer.runner.k8s.podTemplate.podSpec1=/path/to/podSpecWithHighMemRequests.yaml
druid.indexer.runner.k8s.podTemplate.podSpec2=/path/to/podSpecWithLowCpuRequests.yaml

Set the dynamic execution config to define the pod template selection strategy.

{
  "type": "default",
  "podTemplateSelectStrategy": {
    "type": "selectorBased",
    "selectors": [
      {
        "selectionKey": "podSpec1",
        "context.tags": { "userProvidedTag": ["tag1", "tag2"] },
        "dataSource": ["wikipedia"]
      },
      {
        "selectionKey": "podSpec2",
        "type": ["index_kafka"]
      }
    ]
  }
}

Druid selects the pod templates as follows:

Use podSpecWithHighMemRequests.yaml when both of the following conditions are met:
1. The task context contains a tag with the key userProvidedTag that has the value tag1 or tag2.
2. The task targets the wikipedia datasource.
Use podSpecWithLowCpuRequests.yaml when the task type is index_kafka.
Use the basePodSpec.yaml for all other tasks.

In this example, if there is an index_kafka task for the wikipedia datasource with the tag userProvidedTag: tag1, Druid selects the pod template podSpecWithHighMemRequests.yaml.

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
`druid.indexer.runner.capacity`	`Integer`	Number of concurrent jobs that can be sent to Kubernetes.	`2147483647`	No
`druid.indexer.runner.cpuCoreInMicro`	`Integer`	Number of CPU micro core for the task.	`1000`	No

Metrics added

Metric	Description	Dimensions	Normal value
`k8s/peon/startup/time`	Metric indicating the milliseconds for peon pod to startup.	`dataSource`, `taskId`, `taskType`, `groupId`, `taskStatus`, `tags`	Varies

Gotchas

All Druid Pods belonging to one Druid cluster must be inside the same Kubernetes namespace.
You must have a role binding for the overlord's service account that provides the needed permissions for interacting with Kubernetes. An example spec could be:

kind: Role
apiVersion: rbac.authorization.k8s.io/v1
metadata:
  namespace: <druid-namespace>
  name: druid-k8s-task-scheduler
rules:
  - apiGroups: ["batch"]
    resources: ["jobs"]
    verbs: ["get", "watch", "list", "delete", "create"]
  - apiGroups: [""]
    resources: ["pods", "pods/log"]
    verbs: ["get", "watch", "list", "delete", "create"]
---
kind: RoleBinding
apiVersion: rbac.authorization.k8s.io/v1
metadata:
  name: druid-k8s-binding
  namespace: <druid-namespace>
subjects:
  - kind: ServiceAccount
    name: <druid-overlord-k8s-service-account>
    namespace: <druid-namespace>
roleRef:
  kind: Role
  name: druid-k8s-task-scheduler
  apiGroup: rbac.authorization.k8s.io

Migration/Kubernetes and Worker Task Runner

If you are running a cluster with tasks running on middle managers or indexers and want to do a zero downtime migration to mm-less ingestion, the mm-less ingestion system is capable of running in migration mode by reading tasks from middle managers/indexers and Kubernetes and writing tasks to either middle managers or to Kubernetes.

To do this, set the following property. druid.indexer.runner.type: k8sAndWorker (instead of druid.indexer.runner.type: k8s)

Additional Configurations

Property	Possible Values	Description	Default	required
`druid.indexer.runner.k8sAndWorker.runnerStrategy.type`	`String` (e.g., `k8s`, `worker`, `taskType`)	Defines the strategy for task runner selection.	`k8s`	No
`druid.indexer.runner.k8sAndWorker.runnerStrategy.workerType`	`String` (e.g., `httpRemote`, `remote`)	Specifies the variant of the worker task runner to be utilized.	`httpRemote`	No
For `taskType` runner strategy:
`druid.indexer.runner.k8sAndWorker.runnerStrategy.taskType.default`	`String` (e.g., `k8s`, `worker`)	Specifies the default runner to use if no overrides apply. This setting ensures there is always a fallback runner available.	None	No
`druid.indexer.runner.k8sAndWorker.runnerStrategy.taskType.overrides`	`JsonObject`(e.g., `{"index_kafka": "worker"}`)	Defines task-specific overrides for runner types. Each entry sets a task type to a specific runner, allowing fine control.	`{}`	No

How it works​

Configuration​

Dynamic config​

Get dynamic configuration​

URL​

Responses​

Sample request​

Sample response​

Update dynamic configuration​

URL​

Header parameters​

Responses​

Sample request​

Sample response​

Get dynamic configuration history​

URL​

Query parameters​

Responses​

Sample request​

Sample response​

Pod adapters​

Overlord Single Container Pod Adapter/Overlord Multi Container Pod Adapter​

Custom Template Pod Adapter​

Pod template selection​

Select based on task type​

Select based on one or more conditions​

Example​

Properties​

Metrics added​

Gotchas​

Migration/Kubernetes and Worker Task Runner​

Additional Configurations​

How it works

Configuration

Dynamic config

Get dynamic configuration

URL

Responses

Sample request

Sample response

Update dynamic configuration

URL

Header parameters

Responses

Sample request

Sample response

Get dynamic configuration history

URL

Query parameters

Responses

Sample request

Sample response

Pod adapters

Overlord Single Container Pod Adapter/Overlord Multi Container Pod Adapter

Custom Template Pod Adapter

Pod template selection

Select based on task type

Select based on one or more conditions

Example

Properties

Metrics added

Gotchas

Migration/Kubernetes and Worker Task Runner

Additional Configurations