---
title: Advanced Elasticsearch node scheduling
description: Elastic Cloud on Kubernetes (ECK) offers full control over Elasticsearch cluster nodes scheduling by combining Elasticsearch configuration with Kubernetes...
url: https://www.elastic.co/elastic/docs-builder/docs/3065/deploy-manage/deploy/cloud-on-k8s/advanced-elasticsearch-node-scheduling
products:
- Elastic Cloud on Kubernetes
applies_to:
- Elastic Cloud on Kubernetes: Generally available
---
# Advanced Elasticsearch node scheduling
Elastic Cloud on Kubernetes (ECK) offers full control over Elasticsearch cluster nodes scheduling by combining Elasticsearch configuration with Kubernetes scheduling options:
- [Define Elasticsearch nodes roles](#k8s-define-elasticsearch-nodes-roles)
- [Pod affinity and anti-affinity](#k8s-affinity-options)
- [Topology spread constraints and availability zone awareness](#k8s-availability-zone-awareness)
- [Hot-warm topologies](#k8s-hot-warm-topologies)
You can combine these features to deploy a production-grade Elasticsearch cluster.
## Define Elasticsearch nodes roles
You can configure Elasticsearch nodes with [one or multiple roles](https://docs-v3-preview.elastic.dev/elastic/docs-builder/docs/3065/reference/elasticsearch/configuration-reference/node-settings).
You can use [YAML anchors](https://yaml.org/spec/1.2/spec.html#id2765878) to declare the configuration change once and reuse it across all the node sets.
This allows you to describe an Elasticsearch cluster with 3 dedicated master nodes, for example:
```yaml
apiVersion: elasticsearch.k8s.elastic.co/v1
kind: Elasticsearch
metadata:
name: quickstart
spec:
version: 9.3.3
nodeSets:
# 3 dedicated master nodes
- name: master
count: 3
config:
node.roles: ["master"]
# 3 ingest-data nodes
- name: ingest-data
count: 3
config:
node.roles: ["data", "ingest"]
```
## Affinity options
You can set up various [affinity and anti-affinity options](https://kubernetes.io/docs/concepts/configuration/assign-pod-node/#affinity-and-anti-affinity) through the `podTemplate` section of the Elasticsearch resource specification.
### A single Elasticsearch node per Kubernetes host (default)
To avoid scheduling several Elasticsearch nodes from the same cluster on the same host, use a `podAntiAffinity` rule based on the hostname and the cluster name label:
```yaml
apiVersion: elasticsearch.k8s.elastic.co/v1
kind: Elasticsearch
metadata:
name: quickstart
spec:
version: 9.3.3
nodeSets:
- name: default
count: 3
podTemplate:
spec:
affinity:
podAntiAffinity:
preferredDuringSchedulingIgnoredDuringExecution:
- weight: 100
podAffinityTerm:
labelSelector:
matchLabels:
elasticsearch.k8s.elastic.co/cluster-name: quickstart
topologyKey: kubernetes.io/hostname
```
This is ECK default behavior if you don’t specify any `affinity` option. To explicitly disable the default behavior, set an empty affinity object:
```yaml
apiVersion: elasticsearch.k8s.elastic.co/v1
kind: Elasticsearch
metadata:
name: quickstart
spec:
version: 9.3.3
nodeSets:
- name: default
count: 3
podTemplate:
spec:
affinity: {}
```
The default affinity is using `preferredDuringSchedulingIgnoredDuringExecution`, which acts as best effort and won’t prevent an Elasticsearch node from being scheduled on a host if there are no other hosts available. Scheduling a 4-nodes Elasticsearch cluster on a 3-host Kubernetes cluster would then successfully schedule 2 Elasticsearch nodes on the same host. To enforce a strict single node per host, specify `requiredDuringSchedulingIgnoredDuringExecution` instead:
```yaml
apiVersion: elasticsearch.k8s.elastic.co/v1
kind: Elasticsearch
metadata:
name: quickstart
spec:
version: 9.3.3
nodeSets:
- name: default
count: 3
podTemplate:
spec:
affinity:
podAntiAffinity:
requiredDuringSchedulingIgnoredDuringExecution:
- labelSelector:
matchLabels:
elasticsearch.k8s.elastic.co/cluster-name: quickstart
topologyKey: kubernetes.io/hostname
```
### Local Persistent Volume constraints
By default, volumes can be bound to a Pod before the Pod gets scheduled to a particular Kubernetes node. This can be a problem if the PersistentVolume can only be accessed from a particular host or set of hosts. Local persistent volumes are a good example: they are accessible from a single host. If the Pod gets scheduled to a different host based on any affinity or anti-affinity rule, the volume may not be available.
To solve this problem, you can [set the Volume Binding Mode](https://kubernetes.io/docs/concepts/storage/storage-classes/#volume-binding-mode) of the `StorageClass` you are using. Make sure `volumeBindingMode: WaitForFirstConsumer` is set, [especially if you are using local persistent volumes](https://kubernetes.io/docs/concepts/storage/volumes/#local).
```yaml
kind: StorageClass
apiVersion: storage.k8s.io/v1
metadata:
name: local-storage
provisioner: kubernetes.io/no-provisioner
volumeBindingMode: WaitForFirstConsumer
```
### Node affinity
To restrict the scheduling to a particular set of Kubernetes nodes based on labels, use a [NodeSelector](https://kubernetes.io/docs/concepts/configuration/assign-pod-node/#nodeselector). The following example schedules Elasticsearch Pods on Kubernetes nodes tagged with both labels `diskType: ssd` and `environment: production`.
```yaml
apiVersion: elasticsearch.k8s.elastic.co/v1
kind: Elasticsearch
metadata:
name: quickstart
spec:
version: 9.3.3
nodeSets:
- name: default
count: 3
podTemplate:
spec:
nodeSelector:
diskType: ssd
environment: production
```
You can achieve the same (and more) with [node affinity](https://kubernetes.io/docs/concepts/configuration/assign-pod-node/#node-affinity-beta-feature):
```yaml
apiVersion: elasticsearch.k8s.elastic.co/v1
kind: Elasticsearch
metadata:
name: quickstart
spec:
version: 9.3.3
nodeSets:
- name: default
count: 3
podTemplate:
spec:
affinity:
nodeAffinity:
requiredDuringSchedulingIgnoredDuringExecution:
nodeSelectorTerms:
- matchExpressions:
- key: environment
operator: In
values:
- e2e
- production
preferredDuringSchedulingIgnoredDuringExecution:
- weight: 1
preference:
matchExpressions:
- key: diskType
operator: In
values:
- ssd
```
This example restricts Elasticsearch nodes so they are only scheduled on Kubernetes hosts tagged with `environment: e2e` or `environment: production`. It favors nodes tagged with `diskType: ssd`.
## Topology spread constraints and availability zone awareness
Starting with ECK 2.0 the operator can make Kubernetes Node labels available as Pod annotations. It can be used to make information, such as logical failure domains, available in a running Pod. Combined with [Elasticsearch shard allocation awareness](https://docs-v3-preview.elastic.dev/elastic/docs-builder/docs/3065/reference/elasticsearch/configuration-reference/cluster-level-shard-allocation-routing-settings) and [Kubernetes topology spread constraints](https://kubernetes.io/docs/concepts/workloads/pods/pod-topology-spread-constraints/), you can create an availability zone-aware Elasticsearch cluster.
### Exposing Kubernetes node topology labels in Pods
Starting with Kubernetes 1.35 and later, the `PodTopologyLabelsAdmission` feature is enabled by default. As a result, the labels `topology.kubernetes.io/region` and `topology.kubernetes.io/zone` from the node are automatically propagated as labels on Pods. This means that you can skip using the `eck.k8s.elastic.co/downward-node-labels` annotation and avoid making additional configuration changes to expose these topology labels in your Pods. In this situation, you can skip the first two steps described below. Additionally, in this scenario, node labels appear as Pod labels rather than annotations.
1. First, ensure that the operator’s flag `exposed-node-labels` contains the list of the Kubernetes node labels that should be exposed in the Elasticsearch Pods. If you are using the provided installation manifest, or the Helm chart, then this flag is already preset with two wildcard patterns for well-known node labels that describe Kubernetes cluster topology, like `topology.kubernetes.io/.*` and `failure-domain.beta.kubernetes.io/.*`.
2. On the Elasticsearch resources set the `eck.k8s.elastic.co/downward-node-labels` annotations with the list of the Kubernetes node labels that should be copied as Pod annotations.
3. Use the [Kubernetes downward API](https://kubernetes.io/docs/tasks/inject-data-application/downward-api-volume-expose-pod-information/) in the `podTemplate` to make those annotations available as environment variables in Elasticsearch Pods.
Refer to the next section or to the [Elasticsearch sample resource in the ECK source repository](https://github.com/elastic/cloud-on-k8s/tree/3.3/config/samples/elasticsearch/elasticsearch.yaml) for a complete example.
### Using node topology labels, Kubernetes topology spread constraints, and Elasticsearch shard allocation awareness
The following example demonstrates how to use the `topology.kubernetes.io/zone` node labels to spread a NodeSet across the availability zones of a Kubernetes cluster.
Note that by default ECK creates a `k8s_node_name` attribute with the name of the Kubernetes node running the Pod, and configures Elasticsearch to use this attribute. This ensures that Elasticsearch allocates primary and replica shards to Pods running on different Kubernetes nodes and never to Pods that are scheduled onto the same Kubernetes node. To preserve this behavior while making Elasticsearch aware of the availability zone, include the `k8s_node_name` attribute in the comma-separated `cluster.routing.allocation.awareness.attributes` list.
```yaml
apiVersion: elasticsearch.k8s.elastic.co/v1
kind: Elasticsearch
metadata:
annotations:
eck.k8s.elastic.co/downward-node-labels: "topology.kubernetes.io/zone"
name: quickstart
spec:
version: 9.3.3
nodeSets:
- name: default
count: 3
config:
node.attr.zone: ${ZONE}
cluster.routing.allocation.awareness.attributes: k8s_node_name,zone
podTemplate:
spec:
containers:
- name: elasticsearch
env:
- name: ZONE
valueFrom:
fieldRef:
fieldPath: metadata.annotations['topology.kubernetes.io/zone']
topologySpreadConstraints:
- maxSkew: 1
topologyKey: topology.kubernetes.io/zone
whenUnsatisfiable: DoNotSchedule
labelSelector:
matchLabels:
elasticsearch.k8s.elastic.co/cluster-name: quickstart
elasticsearch.k8s.elastic.co/statefulset-name: quickstart-es-default
```
This example relies on:
- Kubernetes nodes in each zone being labeled accordingly. `topology.kubernetes.io/zone` [is standard](https://kubernetes.io/docs/concepts/configuration/assign-pod-node/#interlude-built-in-node-labels), but any label can be used.
- [Pod topology spread constraints](https://kubernetes.io/docs/concepts/workloads/pods/pod-topology-spread-constraints/) to spread the Pods across availability zones in the Kubernetes cluster.
- Elasticsearch configured to [allocate shards based on node attributes](https://docs-v3-preview.elastic.dev/elastic/docs-builder/docs/3065/reference/elasticsearch/configuration-reference/cluster-level-shard-allocation-routing-settings). Here we specified `node.attr.zone`, but any attribute name can be used. `node.attr.rack_id` is another common example.
## Hot-warm topologies
By combining [Elasticsearch shard allocation awareness](https://docs-v3-preview.elastic.dev/elastic/docs-builder/docs/3065/reference/elasticsearch/configuration-reference/cluster-level-shard-allocation-routing-settings) with [Kubernetes node affinity](https://kubernetes.io/docs/concepts/configuration/assign-pod-node/#node-affinity-beta-feature), you can set up an Elasticsearch cluster with hot-warm topology:
```yaml
apiVersion: elasticsearch.k8s.elastic.co/v1
kind: Elasticsearch
metadata:
name: quickstart
spec:
version: 9.3.3
nodeSets:
# hot nodes, with high CPU and fast IO
- name: hot
count: 3
config:
node.roles: ["data_hot", "ingest", "master"]
podTemplate:
spec:
containers:
- name: elasticsearch
resources:
limits:
memory: 16Gi
cpu: 4
affinity:
nodeAffinity:
requiredDuringSchedulingIgnoredDuringExecution:
nodeSelectorTerms:
- matchExpressions:
- key: beta.kubernetes.io/instance-type
operator: In
values:
- highio
volumeClaimTemplates:
- metadata:
name: elasticsearch-data
spec:
accessModes:
- ReadWriteOnce
resources:
requests:
storage: 1Ti
storageClassName: local-storage
# warm nodes, with high storage
- name: warm
count: 3
config:
node.roles: ["data_warm"]
podTemplate:
spec:
containers:
- name: elasticsearch
resources:
limits:
memory: 16Gi
cpu: 2
affinity:
nodeAffinity:
requiredDuringSchedulingIgnoredDuringExecution:
nodeSelectorTerms:
- matchExpressions:
- key: beta.kubernetes.io/instance-type
operator: In
values:
- highstorage
volumeClaimTemplates:
- metadata:
name: elasticsearch-data
spec:
accessModes:
- ReadWriteOnce
resources:
requests:
storage: 10Ti
storageClassName: local-storage
```
In this example, we configure two groups of Elasticsearch nodes:
- The first group has the `data` attribute set to `hot`. It is intended to run on hosts with high CPU resources and fast IO (SSD). Pods can only be scheduled on Kubernetes nodes labeled with `beta.kubernetes.io/instance-type: highio` (to adapt to the labels of your Kubernetes nodes).
- The second group has the `data` attribute set to `warm`. It is intended to run on hosts with larger but maybe slower storage. Pods can only be scheduled on nodes labeled with `beta.kubernetes.io/instance-type: highstorage`.
This example uses [Local Persistent Volumes](https://kubernetes.io/docs/concepts/storage/volumes/#local) for both groups, but can be adapted to use high-performance volumes for `hot` Elasticsearch nodes and high-storage volumes for `warm` Elasticsearch nodes.
Finally, set up [Index Lifecycle Management](https://www.elastic.co/elastic/docs-builder/docs/3065/manage-data/lifecycle/index-lifecycle-management) policies on your indices, [optimizing for hot-warm architectures](https://www.elastic.co/blog/implementing-hot-warm-cold-in-elasticsearch-with-index-lifecycle-management).