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4.8.2. Private clusters

If your environment does not require an external Internet connection, you can deploy a private OpenShift Container Platform cluster that does not expose external endpoints. Private clusters are accessible from only an internal network and are not visible to the Internet.

By default, OpenShift Container Platform is provisioned to use publicly-accessible DNS and endpoints. A private cluster sets the DNS, Ingress Controller, and API server to private when you deploy your cluster. This means that the cluster resources are only accessible from your internal network and are not visible to the internet.

To deploy a private cluster, you must use existing networking that meets your requirements. Your cluster resources might be shared between other clusters on the network.

Additionally, you must deploy a private cluster from a machine that has access the API services for the cloud you provision to, the hosts on the network that you provision, and to the internet to obtain installation media. You can use any machine that meets these access requirements and follows your company’s guidelines. For example, this machine can be a bastion host on your cloud network or a machine that has access to the network through a VPN.

4.8.2.1. Private clusters in GCP

To create a private cluster on Google Cloud Platform (GCP), you must provide an existing private VPC and subnets to host the cluster. The installation program must also be able to resolve the DNS records that the cluster requires. The installation program configures the Ingress Operator and API server for only internal traffic.

The cluster still requires access to Internet to access the GCP APIs.

The following items are not required or created when you install a private cluster:

  • Public subnets
  • Public network load balancers, which support public ingress
  • A public DNS zone that matches the baseDomain for the cluster

The installation program does use the baseDomain that you specify to create a private DNS zone and the required records for the cluster. The cluster is configured so that the Operators do not create public records for the cluster and all cluster machines are placed in the private subnets that you specify.

Because it is not possible to limit access to external load balancers based on source tags, the private cluster uses only internal load balancers to allow access to internal instances.

The internal load balancer relies on instance groups rather than the target pools that the network load balancers use. The installation program creates instance groups for each zone, even if there is no instance in that group.

  • The cluster IP address is internal only.
  • One forwarding rule manages both the Kubernetes API and machine config server ports.
  • The backend service is comprised of each zone’s instance group and, while it exists, the bootstrap instance group.
  • The firewall uses a single rule that is based on only internal source ranges.
4.8.2.1.1. Limitations

No health check for the Machine config server, /healthz, runs because of a difference in load balancer functionality. Two internal load balancers cannot share a single IP address, but two network load balancers can share a single external IP address. Instead, the health of an instance is determined entirely by the /readyz check on port 6443.