Creating infrastructure nodes - Working with nodes | Nodes

OpenShift Container Platform infrastructure components
- Creating an infrastructure node

You can use the advanced machine management and scaling capabilities only in clusters where the Machine API is operational. Clusters with user-provisioned infrastructure require additional validation and configuration to use the Machine API.

Clusters with the infrastructure platform type none cannot use the Machine API. This limitation applies even if the compute machines that are attached to the cluster are installed on a platform that supports the feature. This parameter cannot be changed after installation.

To view the platform type for your cluster, run the following command:

$ oc get infrastructure cluster -o jsonpath='{.status.platform}'

You can use infrastructure machine sets to create machines that host only infrastructure components, such as the default router, the integrated container image registry, and the components for cluster metrics and monitoring. These infrastructure machines are not counted toward the total number of subscriptions that are required to run the environment.

In a production deployment, it is recommended that you deploy at least three machine sets to hold infrastructure components. Both OpenShift Logging and Red Hat OpenShift Service Mesh deploy Elasticsearch, which requires three instances to be installed on different nodes. Each of these nodes can be deployed to different availability zones for high availability. This configuration requires three different machine sets, one for each availability zone. In global Azure regions that do not have multiple availability zones, you can use availability sets to ensure high availability.

After adding the NoSchedule taint on the infrastructure node, existing DNS pods running on that node are marked as misscheduled. You must either delete or add toleration on misscheduled DNS pods.

OpenShift Container Platform infrastructure components

Each self-managed Red Hat OpenShift subscription includes entitlements for OpenShift Container Platform and other OpenShift-related components. These entitlements are included for running OpenShift Container Platform control plane and infrastructure workloads and do not need to be accounted for during sizing.

To qualify as an infrastructure node and use the included entitlement, only components that are supporting the cluster, and not part of an end-user application, can run on those instances. Examples include the following components:

Kubernetes and OpenShift Container Platform control plane services
The default router
The integrated container image registry
The HAProxy-based ingress Controller
The cluster metrics collection, or monitoring service, including components for monitoring user-defined projects
Cluster aggregated logging
Red Hat Quay
Red Hat OpenShift Data Foundation
Red Hat Advanced Cluster Management for Kubernetes
Red Hat Advanced Cluster Security for Kubernetes
Red Hat OpenShift GitOps
Red Hat OpenShift Pipelines
Red Hat OpenShift Service Mesh

Any node that runs any other container, pod, or component is a worker node that your subscription must cover.

For information about infrastructure nodes and which components can run on infrastructure nodes, see the "Red Hat OpenShift control plane and infrastructure nodes" section in the OpenShift sizing and subscription guide for enterprise Kubernetes document.

To create an infrastructure node, you can use a machine set, label the node, or use a machine config pool.

Creating an infrastructure node

See Creating infrastructure machine sets for installer-provisioned infrastructure environments or for any cluster where the control plane nodes are managed by the machine API.

Requirements of the cluster dictate that infrastructure, also called infra nodes, be provisioned. The installer only provides provisions for control plane and worker nodes. Worker nodes can be designated as infrastructure nodes or application, also called app, nodes through labeling.

Procedure

Add a label to the worker node that you want to act as application node:
```
$ oc label node <node-name> node-role.kubernetes.io/app=""
```
Add a label to the worker nodes that you want to act as infrastructure nodes:
```
$ oc label node <node-name> node-role.kubernetes.io/infra=""
```
Check to see if applicable nodes now have the infra role and app roles:
```
$ oc get nodes
```

Create a default cluster-wide node selector. The default node selector is applied to pods created in all namespaces. This creates an intersection with any existing node selectors on a pod, which additionally constrains the pod’s selector.

If the default node selector key conflicts with the key of a pod’s label, then the default node selector is not applied.

However, do not set a default node selector that might cause a pod to become unschedulable. For example, setting the default node selector to a specific node role, such as node-role.kubernetes.io/infra="", when a pod’s label is set to a different node role, such as node-role.kubernetes.io/master="", can cause the pod to become unschedulable. For this reason, use caution when setting the default node selector to specific node roles.

You can alternatively use a project node selector to avoid cluster-wide node selector key conflicts.

Edit the Scheduler object:
```
$ oc edit scheduler cluster
```

Add the defaultNodeSelector field with the appropriate node selector:

apiVersion: config.openshift.io/v1
kind: Scheduler
metadata:
  name: cluster
spec:
  defaultNodeSelector: node-role.kubernetes.io/infra="" (1)
# ...

1	This example node selector deploys pods on infrastructure nodes by default.

Save the file to apply the changes.

You can now move infrastructure resources to the newly labeled infra nodes.

Additional resources

Moving resources to infrastructure machine sets