Using node selectors to move logging resources - Scheduling resources | Logging

About node selectors
Moving logging resources
Additional resources

A node selector specifies a map of key/value pairs that are defined using custom labels on nodes and selectors specified in pods.

For the pod to be eligible to run on a node, the pod must have the same key/value node selector as the label on the node.

About node selectors

You can use node selectors on pods and labels on nodes to control where the pod is scheduled. With node selectors, OKD schedules the pods on nodes that contain matching labels.

You can use a node selector to place specific pods on specific nodes, cluster-wide node selectors to place new pods on specific nodes anywhere in the cluster, and project node selectors to place new pods in a project on specific nodes.

For example, as a cluster administrator, you can create an infrastructure where application developers can deploy pods only onto the nodes closest to their geographical location by including a node selector in every pod they create. In this example, the cluster consists of five data centers spread across two regions. In the U.S., label the nodes as us-east, us-central, or us-west. In the Asia-Pacific region (APAC), label the nodes as apac-east or apac-west. The developers can add a node selector to the pods they create to ensure the pods get scheduled on those nodes.

A pod is not scheduled if the Pod object contains a node selector, but no node has a matching label.

If you are using node selectors and node affinity in the same pod configuration, the following rules control pod placement onto nodes:

If you configure both nodeSelector and nodeAffinity, both conditions must be satisfied for the pod to be scheduled onto a candidate node.
If you specify multiple nodeSelectorTerms associated with nodeAffinity types, then the pod can be scheduled onto a node if one of the nodeSelectorTerms is satisfied.
If you specify multiple matchExpressions associated with nodeSelectorTerms, then the pod can be scheduled onto a node only if all matchExpressions are satisfied.

Node selectors on specific pods and nodes

You can control which node a specific pod is scheduled on by using node selectors and labels.

To use node selectors and labels, first label the node to avoid pods being descheduled, then add the node selector to the pod.

You cannot add a node selector directly to an existing scheduled pod. You must label the object that controls the pod, such as deployment config.

For example, the following Node object has the region: east label:

Sample Node object with a label

kind: Node
apiVersion: v1
metadata:
  name: s1
  selfLink: /api/v1/nodes/ip-10-0-131-14.ec2.internal
  uid: 7bc2580a-8b8e-11e9-8e01-021ab4174c74
  resourceVersion: '478704'
  creationTimestamp: '2019-06-10T14:46:08Z'
  labels:
    kubernetes.io/os: linux
    failure-domain.beta.kubernetes.io/zone: us-east-1a
    node.openshift.io/os_version: '4.5'
    node-role.kubernetes.io/worker: ''
    failure-domain.beta.kubernetes.io/region: us-east-1
    node.openshift.io/os_id: fedora
    beta.kubernetes.io/instance-type: m4.large
    kubernetes.io/hostname: ip-10-0-131-14
    beta.kubernetes.io/arch: amd64
    region: east (1)
    type: user-node
#...

1	Labels to match the pod node selector.

A pod has the type: user-node,region: east node selector:

Sample Pod object with node selectors

apiVersion: v1
kind: Pod
metadata:
  name: s1
#...
spec:
  nodeSelector: (1)
    region: east
    type: user-node
#...

1	Node selectors to match the node label. The node must have a label for each node selector.

When you create the pod using the example pod spec, it can be scheduled on the example node.

Default cluster-wide node selectors

With default cluster-wide node selectors, when you create a pod in that cluster, OKD adds the default node selectors to the pod and schedules the pod on nodes with matching labels.

For example, the following Scheduler object has the default cluster-wide region=east and type=user-node node selectors:

Example Scheduler Operator Custom Resource

apiVersion: config.openshift.io/v1
kind: Scheduler
metadata:
  name: cluster
#...
spec:
  defaultNodeSelector: type=user-node,region=east
#...

A node in that cluster has the type=user-node,region=east labels:

Example Node object

apiVersion: v1
kind: Node
metadata:
  name: ci-ln-qg1il3k-f76d1-hlmhl-worker-b-df2s4
#...
  labels:
    region: east
    type: user-node
#...

Example Pod object with a node selector

apiVersion: v1
kind: Pod
metadata:
  name: s1
#...
spec:
  nodeSelector:
    region: east
#...

When you create the pod using the example pod spec in the example cluster, the pod is created with the cluster-wide node selector and is scheduled on the labeled node:

Example pod list with the pod on the labeled node

NAME     READY   STATUS    RESTARTS   AGE   IP           NODE                                       NOMINATED NODE   READINESS GATES
pod-s1   1/1     Running   0          20s   10.131.2.6   ci-ln-qg1il3k-f76d1-hlmhl-worker-b-df2s4   <none>           <none>

If the project where you create the pod has a project node selector, that selector takes preference over a cluster-wide node selector. Your pod is not created or scheduled if the pod does not have the project node selector.

Project node selectors

With project node selectors, when you create a pod in this project, OKD adds the node selectors to the pod and schedules the pods on a node with matching labels. If there is a cluster-wide default node selector, a project node selector takes preference.

For example, the following project has the region=east node selector:

Example Namespace object

apiVersion: v1
kind: Namespace
metadata:
  name: east-region
  annotations:
    openshift.io/node-selector: "region=east"
#...

The following node has the type=user-node,region=east labels:

Example Node object

apiVersion: v1
kind: Node
metadata:
  name: ci-ln-qg1il3k-f76d1-hlmhl-worker-b-df2s4
#...
  labels:
    region: east
    type: user-node
#...

When you create the pod using the example pod spec in this example project, the pod is created with the project node selectors and is scheduled on the labeled node:

Example Pod object

apiVersion: v1
kind: Pod
metadata:
  namespace: east-region
#...
spec:
  nodeSelector:
    region: east
    type: user-node
#...

Example pod list with the pod on the labeled node

NAME     READY   STATUS    RESTARTS   AGE   IP           NODE                                       NOMINATED NODE   READINESS GATES
pod-s1   1/1     Running   0          20s   10.131.2.6   ci-ln-qg1il3k-f76d1-hlmhl-worker-b-df2s4   <none>           <none>

A pod in the project is not created or scheduled if the pod contains different node selectors. For example, if you deploy the following pod into the example project, it is not be created:

Example Pod object with an invalid node selector

apiVersion: v1
kind: Pod
metadata:
  name: west-region
#...
spec:
  nodeSelector:
    region: west
#...

Moving logging resources

You can configure the Red Hat OpenShift Logging Operator to deploy the pods for logging components, such as Elasticsearch and Kibana, to different nodes. You cannot move the Red Hat OpenShift Logging Operator pod from its installed location.

For example, you can move the Elasticsearch pods to a separate node because of high CPU, memory, and disk requirements.

Prerequisites

You have installed the Red Hat OpenShift Logging Operator and the OpenShift Elasticsearch Operator.

Procedure

Edit the ClusterLogging custom resource (CR) in the openshift-logging project:

$ oc edit ClusterLogging instance

Example ClusterLogging CR

apiVersion: logging.openshift.io/v1
kind: ClusterLogging
# ...
spec:
  logStore:
    elasticsearch:
      nodeCount: 3
      nodeSelector: (1)
        node-role.kubernetes.io/infra: ''
      tolerations:
      - effect: NoSchedule
        key: node-role.kubernetes.io/infra
        value: reserved
      - effect: NoExecute
        key: node-role.kubernetes.io/infra
        value: reserved
      redundancyPolicy: SingleRedundancy
      resources:
        limits:
          cpu: 500m
          memory: 16Gi
        requests:
          cpu: 500m
          memory: 16Gi
      storage: {}
    type: elasticsearch
  managementState: Managed
  visualization:
    kibana:
      nodeSelector: (1)
        node-role.kubernetes.io/infra: ''
      tolerations:
      - effect: NoSchedule
        key: node-role.kubernetes.io/infra
        value: reserved
      - effect: NoExecute
        key: node-role.kubernetes.io/infra
        value: reserved
      proxy:
        resources: null
      replicas: 1
      resources: null
    type: kibana
# ...

1	Add a `nodeSelector` parameter with the appropriate value to the component you want to move. You can use a `nodeSelector` in the format shown or use `<key>: <value>` pairs, based on the value specified for the node. If you added a taint to the infrasructure node, also add a matching toleration.

Verification

To verify that a component has moved, you can use the oc get pod -o wide command.

For example:

You want to move the Kibana pod from the ip-10-0-147-79.us-east-2.compute.internal node:

$ oc get pod kibana-5b8bdf44f9-ccpq9 -o wide

Example output

NAME                      READY   STATUS    RESTARTS   AGE   IP            NODE                                        NOMINATED NODE   READINESS GATES
kibana-5b8bdf44f9-ccpq9   2/2     Running   0          27s   10.129.2.18   ip-10-0-147-79.us-east-2.compute.internal   <none>           <none>

You want to move the Kibana pod to the ip-10-0-139-48.us-east-2.compute.internal node, a dedicated infrastructure node:

$ oc get nodes

Example output

NAME                                         STATUS   ROLES          AGE   VERSION
ip-10-0-133-216.us-east-2.compute.internal   Ready    master         60m   v1.24.0
ip-10-0-139-146.us-east-2.compute.internal   Ready    master         60m   v1.24.0
ip-10-0-139-192.us-east-2.compute.internal   Ready    worker         51m   v1.24.0
ip-10-0-139-241.us-east-2.compute.internal   Ready    worker         51m   v1.24.0
ip-10-0-147-79.us-east-2.compute.internal    Ready    worker         51m   v1.24.0
ip-10-0-152-241.us-east-2.compute.internal   Ready    master         60m   v1.24.0
ip-10-0-139-48.us-east-2.compute.internal    Ready    infra          51m   v1.24.0

Note that the node has a node-role.kubernetes.io/infra: '' label:

$ oc get node ip-10-0-139-48.us-east-2.compute.internal -o yaml

Example output

kind: Node
apiVersion: v1
metadata:
  name: ip-10-0-139-48.us-east-2.compute.internal
  selfLink: /api/v1/nodes/ip-10-0-139-48.us-east-2.compute.internal
  uid: 62038aa9-661f-41d7-ba93-b5f1b6ef8751
  resourceVersion: '39083'
  creationTimestamp: '2020-04-13T19:07:55Z'
  labels:
    node-role.kubernetes.io/infra: ''
...

To move the Kibana pod, edit the ClusterLogging CR to add a node selector:

apiVersion: logging.openshift.io/v1
kind: ClusterLogging
# ...
spec:
# ...
  visualization:
    kibana:
      nodeSelector: (1)
        node-role.kubernetes.io/infra: ''
      proxy:
        resources: null
      replicas: 1
      resources: null
    type: kibana

1	Add a node selector to match the label in the node specification.

After you save the CR, the current Kibana pod is terminated and new pod is deployed:

$ oc get pods

Example output

NAME                                            READY   STATUS        RESTARTS   AGE
cluster-logging-operator-84d98649c4-zb9g7       1/1     Running       0          29m
elasticsearch-cdm-hwv01pf7-1-56588f554f-kpmlg   2/2     Running       0          28m
elasticsearch-cdm-hwv01pf7-2-84c877d75d-75wqj   2/2     Running       0          28m
elasticsearch-cdm-hwv01pf7-3-f5d95b87b-4nx78    2/2     Running       0          28m
collector-42dzz                                 1/1     Running       0          28m
collector-d74rq                                 1/1     Running       0          28m
collector-m5vr9                                 1/1     Running       0          28m
collector-nkxl7                                 1/1     Running       0          28m
collector-pdvqb                                 1/1     Running       0          28m
collector-tflh6                                 1/1     Running       0          28m
kibana-5b8bdf44f9-ccpq9                         2/2     Terminating   0          4m11s
kibana-7d85dcffc8-bfpfp                         2/2     Running       0          33s

The new pod is on the ip-10-0-139-48.us-east-2.compute.internal node:

$ oc get pod kibana-7d85dcffc8-bfpfp -o wide

Example output

NAME                      READY   STATUS        RESTARTS   AGE   IP            NODE                                        NOMINATED NODE   READINESS GATES
kibana-7d85dcffc8-bfpfp   2/2     Running       0          43s   10.131.0.22   ip-10-0-139-48.us-east-2.compute.internal   <none>           <none>

After a few moments, the original Kibana pod is removed.

$ oc get pods

Example output

NAME                                            READY   STATUS    RESTARTS   AGE
cluster-logging-operator-84d98649c4-zb9g7       1/1     Running   0          30m
elasticsearch-cdm-hwv01pf7-1-56588f554f-kpmlg   2/2     Running   0          29m
elasticsearch-cdm-hwv01pf7-2-84c877d75d-75wqj   2/2     Running   0          29m
elasticsearch-cdm-hwv01pf7-3-f5d95b87b-4nx78    2/2     Running   0          29m
collector-42dzz                                 1/1     Running   0          29m
collector-d74rq                                 1/1     Running   0          29m
collector-m5vr9                                 1/1     Running   0          29m
collector-nkxl7                                 1/1     Running   0          29m
collector-pdvqb                                 1/1     Running   0          29m
collector-tflh6                                 1/1     Running   0          29m
kibana-7d85dcffc8-bfpfp                         2/2     Running   0          62s

Additional resources

Placing pods on specific nodes using node selectors