By default, when you install an Operator, Red Hat OpenShift service on AWS installs the Operator pod to one of your worker nodes randomly. However, there might be situations where you want that pod scheduled on a specific node or set of nodes.
The following examples describe situations where you might want to schedule an Operator pod to a specific node or set of nodes:
-
If you want Operators that work together scheduled on the same host or on hosts located on the same rack
-
If you want Operators dispersed throughout the infrastructure to avoid downtime due to network or hardware issues
You can control where an Operator pod is installed by adding node affinity, pod affinity, or pod anti-affinity constraints to the Operator’s Subscription
object. Node affinity is a set of rules used by the scheduler to determine where a pod can be placed. Pod affinity enables you to ensure that related pods are scheduled to the same node. Pod anti-affinity allows you to prevent a pod from being scheduled on a node.
The following examples show how to use node affinity or pod anti-affinity to install an instance of the Custom Metrics Autoscaler Operator to a specific node in the cluster:
Node affinity example that places the Operator pod on a specific node
apiVersion: operators.coreos.com/v1alpha1
kind: Subscription
metadata:
name: openshift-custom-metrics-autoscaler-operator
namespace: openshift-keda
spec:
name: my-package
source: my-operators
sourceNamespace: operator-registries
config:
affinity:
nodeAffinity: (1)
requiredDuringSchedulingIgnoredDuringExecution:
nodeSelectorTerms:
- matchExpressions:
- key: kubernetes.io/hostname
operator: In
values:
- ip-10-0-163-94.us-west-2.compute.internal
#...
1 |
A node affinity that requires the Operator’s pod to be scheduled on a node named ip-10-0-163-94.us-west-2.compute.internal . |
Node affinity example that places the Operator pod on a node with a specific platform
apiVersion: operators.coreos.com/v1alpha1
kind: Subscription
metadata:
name: openshift-custom-metrics-autoscaler-operator
namespace: openshift-keda
spec:
name: my-package
source: my-operators
sourceNamespace: operator-registries
config:
affinity:
nodeAffinity: (1)
requiredDuringSchedulingIgnoredDuringExecution:
nodeSelectorTerms:
- matchExpressions:
- key: kubernetes.io/arch
operator: In
values:
- arm64
- key: kubernetes.io/os
operator: In
values:
- linux
#...
1 |
A node affinity that requires the Operator’s pod to be scheduled on a node with the kubernetes.io/arch=arm64 and kubernetes.io/os=linux labels. |
Pod affinity example that places the Operator pod on one or more specific nodes
apiVersion: operators.coreos.com/v1alpha1
kind: Subscription
metadata:
name: openshift-custom-metrics-autoscaler-operator
namespace: openshift-keda
spec:
name: my-package
source: my-operators
sourceNamespace: operator-registries
config:
affinity:
podAffinity: (1)
requiredDuringSchedulingIgnoredDuringExecution:
- labelSelector:
matchExpressions:
- key: app
operator: In
values:
- test
topologyKey: kubernetes.io/hostname
#...
1 |
A pod affinity that places the Operator’s pod on a node that has pods with the app=test label. |
Pod anti-affinity example that prevents the Operator pod from one or more specific nodes
apiVersion: operators.coreos.com/v1alpha1
kind: Subscription
metadata:
name: openshift-custom-metrics-autoscaler-operator
namespace: openshift-keda
spec:
name: my-package
source: my-operators
sourceNamespace: operator-registries
config:
affinity:
podAntiAffinity: (1)
requiredDuringSchedulingIgnoredDuringExecution:
- labelSelector:
matchExpressions:
- key: cpu
operator: In
values:
- high
topologyKey: kubernetes.io/hostname
#...
1 |
A pod anti-affinity that prevents the Operator’s pod from being scheduled on a node that has pods with the cpu=high label. |
Procedure
To control the placement of an Operator pod, complete the following steps:
-
Install the Operator as usual.
-
If needed, ensure that your nodes are labeled to properly respond to the affinity.
-
Edit the Operator Subscription
object to add an affinity:
apiVersion: operators.coreos.com/v1alpha1
kind: Subscription
metadata:
name: openshift-custom-metrics-autoscaler-operator
namespace: openshift-keda
spec:
name: my-package
source: my-operators
sourceNamespace: operator-registries
config:
affinity: (1)
nodeAffinity:
requiredDuringSchedulingIgnoredDuringExecution:
nodeSelectorTerms:
- matchExpressions:
- key: kubernetes.io/hostname
operator: In
values:
- ip-10-0-185-229.ec2.internal
#...
1 |
Add a nodeAffinity , podAffinity , or podAntiAffinity . See the Additional resources section that follows for information about creating the affinity. |