Restarting the cluster gracefully

You can restart your OpenShift Container Platform cluster after a graceful shutdown by powering on nodes and verifying cluster health. The cluster returns to normal operations when nodes and Operators are healthy.

Even though the cluster is expected to be functional after the restart, the cluster might not recover due to unexpected conditions:

etcd data corruption during shutdown
Node failure due to hardware
Network connectivity issues

If your cluster fails to recover, follow the steps in "Restoring to an earlier cluster state".

Restarting the cluster

You can restart the cluster after a graceful shutdown by powering on nodes, uncordoning schedulable nodes, and approving pending certificate signing requests (CSRs) if nodes are not ready. The cluster returns to normal operations after all nodes and Operators are healthy.

Prerequisites

You have access to the cluster as a user with the cluster-admin role.
You have gracefully shut down your cluster.

If your cluster fails to recover, follow the steps in "Restoring to an earlier cluster state".

Procedure

Turn on the control plane nodes.
- If you are using the admin.kubeconfig from the cluster installation and the API virtual IP address (VIP) is up, complete the following steps:
  1. Set the KUBECONFIG environment variable to the admin.kubeconfig path.
  2. Uncordon each control plane node in the cluster by running the following command:
    $ oc adm uncordon <node>
- If you do not have access to your admin.kubeconfig credentials, complete the following steps:
  1. Use SSH to connect to a control plane node.
  2. Copy the localhost-recovery.kubeconfig file to the /root directory.
  3. Use that file to uncordon each control plane node in the cluster by running the following command:
    $ oc adm uncordon <node>
Power on any cluster dependencies, such as external storage or a Lightweight Directory Access Protocol (LDAP) server.
Start all cluster machines. Use the appropriate method for your cloud environment to start the machines, for example, from the web console for your cloud provider.

Wait approximately 10 minutes before continuing to check the status of control plane nodes.

Verify that all control plane nodes are ready by running the following command:

$ oc get nodes -l node-role.kubernetes.io/master

The control plane nodes are ready if the status is Ready, as shown in the following output:

NAME                           STATUS   ROLES                  AGE   VERSION
ip-10-0-168-251.ec2.internal   Ready    control-plane,master   75m   v1.35.0
ip-10-0-170-223.ec2.internal   Ready    control-plane,master   75m   v1.35.0
ip-10-0-211-16.ec2.internal    Ready    control-plane,master   75m   v1.35.0

If the control plane nodes are not ready, then check whether there are any pending CSRs that must be approved.
1. Get the list of current CSRs by running the following command:
```
$ oc get csr
```
2. Review the details of each CSR to verify that it is valid by running the following command:
```
$ oc get csr <csr_name> -o jsonpath='{.spec.request}' | base64 -d | openssl req -text -noout
```
  When validating the CSR, verify that the following fields match your infrastructure expectations:
  - Subject / Common Name (CN): Must follow the format system:node:<node_name>, such as system:node:control-plane-0.example.com.
  - Organization (O): Must be exactly system:nodes.
  - Requested Extensions (Extended Key Usage): Must list TLS Web Client Authentication.
    Example output
    Certificate Request: Data: Version: 1 (0x0) Subject: O = system:nodes, CN = system:node:control-plane-0.example.com Subject Public Key Info: Public Key Algorithm: id-ecPublicKey Public-Key: (256 bit) Attributes: Requested Extensions: X509v3 Extended Key Usage: TLS Web Client Authentication
    The process verifies that the certificate is allowed to be used as a client credential for the node.
3. Approve each valid CSR by running the following command:
```
$ oc adm certificate approve <csr_name>
```

After the control plane nodes are ready, verify that all compute nodes are ready by running the following command:

$ oc get nodes -l node-role.kubernetes.io/worker

The compute nodes are ready if the status is Ready, as shown in the following output:

NAME                           STATUS   ROLES    AGE   VERSION
ip-10-0-179-95.ec2.internal    Ready    worker   64m   v1.35.0
ip-10-0-182-134.ec2.internal   Ready    worker   64m   v1.35.0
ip-10-0-250-100.ec2.internal   Ready    worker   64m   v1.35.0

If the compute nodes are not ready, then check whether there are any pending CSRs that must be approved.
1. Get the list of current CSRs by running the following command:
```
$ oc get csr
```
2. Review the details of each CSR to verify the validity of the CSR by running the following command:
```
$ oc get csr <csr_name> -o jsonpath='{.spec.request}' | base64 -d | openssl req -text -noout
```
  Compute node CSRs can be for client certificates (kubelet to API) or serving certificates (API to kubelet). Verify that the following fields match your infrastructure expectations:
  - Subject / Common Name (CN): Must follow the format system:node:<compute_node_name>.
  - Organization (O): Must be exactly system:nodes.
  - Extended Key Usage (EKU): Must list TLS Web Client Authentication (for client requests) or TLS Web Server Authentication (for serving requests).
  - Subject Alternative Name (SAN): For serving certificates, this field must contain the correct internal DNS hostname and the internal IP address of the respective compute node.
    Example output
    Certificate Request: Data: Version: 1 (0x0) Subject: O = system:nodes, CN = system:node:worker-0.example.com Subject Public Key Info: Public Key Algorithm: rsaEncryption Public-Key: (2048 bit) Attributes: Requested Extensions: X509v3 Extended Key Usage: TLS Web Server Authentication X509v3 Subject Alternative Name: DNS:worker-0.example.com, IP Address:10.0.12.34
    This process verifies the validity of the certificate as a server credential for cluster communication.
3. Approve each valid CSR by running the following command:
```
$ oc adm certificate approve <csr_name>
```
After the control plane and compute nodes are ready, mark all the nodes in the cluster as schedulable by running the following command:
```
$ for node in $(oc get nodes -o jsonpath='{.items[*].metadata.name}'); do echo ${node} ; oc adm uncordon ${node} ; done
```

Verification

Check that there are no degraded cluster Operators by running the following command:

$ oc get clusteroperators

Example output
NAME                                       VERSION   AVAILABLE   PROGRESSING   DEGRADED   SINCE
authentication                             4.22.0    True        False         False      59m
cloud-credential                           4.22.0    True        False         False      85m
cluster-autoscaler                         4.22.0    True        False         False      73m
config-operator                            4.22.0    True        False         False      73m
console                                    4.22.0    True        False         False      62m
csi-snapshot-controller                    4.22.0    True        False         False      66m
dns                                        4.22.0    True        False         False      76m
etcd                                       4.22.0    True        False         False      76m
...

Check that all nodes are in the Ready state by running the following command:

$ oc get nodes

Example output
NAME                           STATUS   ROLES                  AGE   VERSION
ip-10-0-168-251.ec2.internal   Ready    control-plane,master   82m   v1.35.0
ip-10-0-170-223.ec2.internal   Ready    control-plane,master   82m   v1.35.0
ip-10-0-179-95.ec2.internal    Ready    worker                 70m   v1.35.0
ip-10-0-182-134.ec2.internal   Ready    worker                 70m   v1.35.0
ip-10-0-211-16.ec2.internal    Ready    control-plane,master   82m   v1.35.0
ip-10-0-250-100.ec2.internal   Ready    worker                 69m   v1.35.0

If the cluster did not start properly, you might need to restore your cluster by using an etcd backup. For more information, see "Restoring to an earlier cluster state".

If the CSRs for new compute nodes that are trying to join the cluster are not approved, investigate the problem:
- Check the Machine Approver logs by entering the following command:
```
$ oc logs -n openshift-cluster-machine-approver -l app=machine-approver
```
- To list all CSRs, enter the following command:
```
$ oc get csr -A
```
If CSRs are pending, you can manually approve them. Manual approval is needed when certificates expired during extended downtime or after cluster recovery scenarios.
1. List any pending CSR requests by entering the following command:
```
$ oc get csr | grep Pending
```
2. Approve pending CSRs by entering the following command:
```
$ oc adm certificate approve csrName
```
To troubleshoot other errors related to CSRs, check the Kube Controller Manager logs by entering the following command:
```
$ oc logs -n openshift-kube-controller-manager -l app=kube-controller-manager
```

Additional resources

Restarting the cluster​

Restarting the cluster