Configuring a private cluster | Post-installation configuration

About private clusters
Setting DNS to private
Setting the ingress Controller to private
Restricting the API server to private

After you install an OpenShift Container Platform version 4.9 cluster, you can set some of its core components to be private.

About private clusters

By default, OpenShift Container Platform is provisioned using publicly-accessible DNS and endpoints. You can set the DNS, ingress Controller, and API server to private after you deploy your private cluster.

If the cluster has any public subnets, load balancer services created by administrators might be publicly accessible. To ensure cluster security, verify that these services are explicitly annotated as private.

DNS

If you install OpenShift Container Platform on installer-provisioned infrastructure, the installation program creates records in a pre-existing public zone and, where possible, creates a private zone for the cluster’s own DNS resolution. In both the public zone and the private zone, the installation program or cluster creates DNS entries for *.apps, for the ingress object, and api, for the API server.

The *.apps records in the public and private zone are identical, so when you delete the public zone, the private zone seamlessly provides all DNS resolution for the cluster.

ingress Controller

Because the default ingress object is created as public, the load balancer is internet-facing and in the public subnets. You can replace the default ingress Controller with an internal one.

API server

By default, the installation program creates appropriate network load balancers for the API server to use for both internal and external traffic.

On Amazon Web Services (AWS), separate public and private load balancers are created. The load balancers are identical except that an additional port is available on the internal one for use within the cluster. Although the installation program automatically creates or destroys the load balancer based on API server requirements, the cluster does not manage or maintain them. As long as you preserve the cluster’s access to the API server, you can manually modify or move the load balancers. For the public load balancer, port 6443 is open and the health check is configured for HTTPS against the /readyz path.

On Google Cloud Platform, a single load balancer is created to manage both internal and external API traffic, so you do not need to modify the load balancer.

On Microsoft Azure, both public and private load balancers are created. However, because of limitations in current implementation, you just retain both load balancers in a private cluster.

Setting DNS to private

After you deploy a cluster, you can modify its DNS to use only a private zone.

Procedure

Review the DNS custom resource for your cluster:

$ oc get dnses.config.openshift.io/cluster -o yaml

Example output

apiVersion: config.openshift.io/v1
kind: DNS
metadata:
  creationTimestamp: "2019-10-25T18:27:09Z"
  generation: 2
  name: cluster
  resourceVersion: "37966"
  selfLink: /apis/config.openshift.io/v1/dnses/cluster
  uid: 0e714746-f755-11f9-9cb1-02ff55d8f976
spec:
  baseDomain: <base_domain>
  privateZone:
    tags:
      Name: <infrastructure_id>-int
      kubernetes.io/cluster/<infrastructure_id>: owned
  publicZone:
    id: Z2XXXXXXXXXXA4
status: {}

Note that the spec section contains both a private and a public zone.

Patch the DNS custom resource to remove the public zone:
```
$ oc patch dnses.config.openshift.io/cluster --type=merge --patch='{"spec": {"publicZone": null}}'
dns.config.openshift.io/cluster patched
```
Because the ingress Controller consults the DNS definition when it creates ingress objects, when you create or modify ingress objects, only private records are created.

DNS records for the existing ingress objects are not modified when you remove the public zone.

Optional: Review the DNS custom resource for your cluster and confirm that the public zone was removed:

$ oc get dnses.config.openshift.io/cluster -o yaml

Example output

apiVersion: config.openshift.io/v1
kind: DNS
metadata:
  creationTimestamp: "2019-10-25T18:27:09Z"
  generation: 2
  name: cluster
  resourceVersion: "37966"
  selfLink: /apis/config.openshift.io/v1/dnses/cluster
  uid: 0e714746-f755-11f9-9cb1-02ff55d8f976
spec:
  baseDomain: <base_domain>
  privateZone:
    tags:
      Name: <infrastructure_id>-int
      kubernetes.io/cluster/<infrastructure_id>-wfpg4: owned
status: {}

Setting the ingress Controller to private

After you deploy a cluster, you can modify its ingress Controller to use only a private zone.

Procedure

Modify the default ingress Controller to use only an internal endpoint:

$ oc replace --force --wait --filename - <<EOF
apiVersion: operator.openshift.io/v1
kind: ingressController
metadata:
  namespace: openshift-ingress-operator
  name: default
spec:
  endpointPublishingStrategy:
    type: LoadBalancerService
    loadBalancer:
      scope: Internal
EOF

Example output

ingresscontroller.operator.openshift.io "default" deleted
ingresscontroller.operator.openshift.io/default replaced

The public DNS entry is removed, and the private zone entry is updated.

Restricting the API server to private

After you deploy a cluster to Amazon Web Services (AWS) or Microsoft Azure, you can reconfigure the API server to use only the private zone.

Prerequisites

Install the OpenShift CLI (oc).
Have access to the web console as a user with admin privileges.

Procedure

In the web portal or console for AWS or Azure, take the following actions:
1. Locate and delete appropriate load balancer component.
  - For AWS, delete the external load balancer. The API DNS entry in the private zone already points to the internal load balancer, which uses an identical configuration, so you do not need to modify the internal load balancer.
  - For Azure, delete the api-internal rule for the load balancer.
2. Delete the api.$clustername.$yourdomain DNS entry in the public zone.

Remove the external load balancers:

You can run the following steps only for an installer-provisioned infrastructure (IPI) cluster. For a user-provisioned infrastructure (UPI) cluster, you must manually remove or disable the external load balancers.

From your terminal, list the cluster machines:

$ oc get machine -n openshift-machine-api

Example output

NAME                            STATE     TYPE        REGION      ZONE         AGE
lk4pj-master-0                  running   m4.xlarge   us-east-1   us-east-1a   17m
lk4pj-master-1                  running   m4.xlarge   us-east-1   us-east-1b   17m
lk4pj-master-2                  running   m4.xlarge   us-east-1   us-east-1a   17m
lk4pj-worker-us-east-1a-5fzfj   running   m4.xlarge   us-east-1   us-east-1a   15m
lk4pj-worker-us-east-1a-vbghs   running   m4.xlarge   us-east-1   us-east-1a   15m
lk4pj-worker-us-east-1b-zgpzg   running   m4.xlarge   us-east-1   us-east-1b   15m

You modify the control plane machines, which contain master in the name, in the following step.

Remove the external load balancer from each control plane machine.
1. Edit a control plane Machine object to remove the reference to the external load balancer:
  $ oc edit machines -n openshift-machine-api <master_name> (1)
  1 Specify the name of the control plane, or master, Machine object to modify.
2. Remove the lines that describe the external load balancer, which are marked in the following example, and save and exit the object specification:
  ... spec: providerSpec: value: ... loadBalancers: - name: lk4pj-ext (1) type: network (1) - name: lk4pj-int type: network
  1 Delete this line.
3. Repeat this process for each of the machines that contains master in the name.