Kubernetes

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

Apache Druid Extension to enable using Kubernetes API Server for node discovery and leader election. This extension allows Druid cluster deployment on Kubernetes without Zookeeper. It allows running multiple Druid clusters within same Kubernetes Cluster, See clusterIdentifier config below.

Configuration

To use this extension please make sure to include druid-kubernetes-extensions in the extensions load list.

This extension works together with HTTP-based segment and task management in Druid. Consequently, following configurations must be set on all Druid nodes.

druid.zk.service.enabled=false druid.serverview.type=http druid.indexer.runner.type=httpRemote druid.discovery.type=k8s

For Node Discovery, Each Druid process running inside a pod "announces" itself by adding few "labels" and "annotations" in the pod spec. Druid process needs to be aware of pod name and namespace which it reads from environment variables POD_NAME and POD_NAMESPACE. These variable names can be changed, see configuration below. But in the end, each pod needs to have self pod name and namespace added as environment variables.

Additionally, this extension has following configuration.

Properties

Property	Possible Values	Description	Default	required
druid.discovery.k8s.clusterIdentifier	string that matches [a-z0-9][a-z0-9-]*[a-z0-9]	Unique identifier for this Druid cluster in Kubernetes e.g. us-west-prod-druid.	None	Yes
druid.discovery.k8s.podNameEnvKey	Pod Env Variable	Pod Env variable whose value is that pod's name.	POD_NAME	No
druid.discovery.k8s.podNamespaceEnvKey	Pod Env Variable	Pod Env variable whose value is that pod's kubernetes namespace.	POD_NAMESPACE	No
druid.discovery.k8s.leaseDuration	Duration	Lease duration used by Leader Election algorithm. Candidates wait for this time before taking over previous Leader.	PT60S	No
druid.discovery.k8s.renewDeadline	Duration	Lease renewal period used by Leader.	PT17S	No
druid.discovery.k8s.retryPeriod	Duration	Retry wait used by Leader Election algorithm on failed operations.	PT5S	No

Gotchas

• Label/Annotation path in each pod spec MUST EXIST, which is easily satisfied if there is at least one label/annotation in the pod spec already. This limitation may be removed in future.
• All Druid Pods belonging to one Druid cluster must be inside same kubernetes namespace.
• All Druid Pods need permissions to be able to add labels to self-pod, List and Watch other Pods, create and read ConfigMap for leader election. Assuming, "default" service account is used by Druid pods, you might need to add following or something similar Kubernetes Role and Role Binding.

apiVersion: rbac.authorization.k8s.io/v1
kind: Role
metadata:
  name: druid-cluster
rules:
- apiGroups:
  - ""
  resources:
  - pods
  - configmaps
  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