Chapter 10. Adding more RHEL compute machines to an OpenShift Container Platform cluster If your OpenShift Container Platform cluster already includes Red Hat Enterprise Linux (RHEL) compute machines, which are also known as worker machines, you can add more RHEL compute machines to it. 10.1. About adding RHEL compute nodes to a cluster In OpenShift Container Platform 4.13, you have the option of using Red Hat Enterprise Linux (RHEL) machines as compute machines in your cluster if you use a user-provisioned or installer-provisioned infrastructure installation on the x86_64 architecture. You must use Red Hat Enterprise Linux CoreOS (RHCOS) machines for the control plane machines in your cluster. If you choose to use RHEL compute machines in your cluster, you are responsible for all operating system life cycle management and maintenance. You must perform system updates, apply patches, and complete all other required tasks. For installer-provisioned infrastructure clusters, you must manually add RHEL compute machines because automatic scaling in installer-provisioned infrastructure clusters adds Red Hat Enterprise Linux CoreOS (RHCOS) compute machines by default. Important Because removing OpenShift Container Platform from a machine in the cluster requires destroying the operating system, you must use dedicated hardware for any RHEL machines that you add to the cluster. Swap memory is disabled on all RHEL machines that you add to your OpenShift Container Platform cluster. You cannot enable swap memory on these machines. 10.2. System requirements for RHEL compute nodes The Red Hat Enterprise Linux (RHEL) compute machine hosts in your OpenShift Container Platform environment must meet the following minimum hardware specifications and system-level requirements: You must have an active OpenShift Container Platform subscription on your Red Hat account. If you do not, contact your sales representative for more information. Production environments must provide compute machines to support your expected workloads. As a cluster administrator, you must calculate the expected workload and add about 10% for overhead. For production environments, allocate enough resources so that a node host failure does not affect your maximum capacity. Each system must meet the following hardware requirements: Physical or virtual system, or an instance running on a public or private IaaS. Base OS: RHEL 8.6 and later with "Minimal" installation option. Important Adding RHEL 7 compute machines to an OpenShift Container Platform cluster is not supported. If you have RHEL 7 compute machines that were previously supported in a past OpenShift Container Platform version, you cannot upgrade them to RHEL 8. You must deploy new RHEL 8 hosts, and the old RHEL 7 hosts should be removed. See the "Deleting nodes" section for more information. For the most recent list of major functionality that has been deprecated or removed within OpenShift Container Platform, refer to the Deprecated and removed features section of the OpenShift Container Platform release notes. NetworkManager 1.0 or later. 1 vCPU. Minimum 8 GB RAM. Minimum 15 GB hard disk space for the file system containing /var/ . Minimum 1 GB hard disk space for the file system containing /usr/local/bin/ . Minimum 1 GB hard disk space for the file system containing its temporary directory. The temporary system directory is determined according to the rules defined in the tempfile module in the Python standard library. Each system must meet any additional requirements for your system provider. For example, if you installed your cluster on VMware vSphere, your disks must be configured according to its storage guidelines and the disk.enableUUID=true attribute must be set. Each system must be able to access the cluster's API endpoints by using DNS-resolvable hostnames. Any network security access control that is in place must allow system access to the cluster's API service endpoints. Additional resources Deleting nodes 10.2.1. Certificate signing requests management Because your cluster has limited access to automatic machine management when you use infrastructure that you provision, you must provide a mechanism for approving cluster certificate signing requests (CSRs) after installation. The kube-controller-manager only approves the kubelet client CSRs. The machine-approver cannot guarantee the validity of a serving certificate that is requested by using kubelet credentials because it cannot confirm that the correct machine issued the request. You must determine and implement a method of verifying the validity of the kubelet serving certificate requests and approving them. 10.3. Preparing an image for your cloud Amazon Machine Images (AMI) are required since various image formats cannot be used directly by AWS. You may use the AMIs that Red Hat has provided, or you can manually import your own images. The AMI must exist before the EC2 instance can be provisioned. You must list the AMI IDs so that the correct RHEL version needed for the compute machines is selected. 10.3.1. Listing latest available RHEL images on AWS AMI IDs correspond to native boot images for AWS. Because an AMI must exist before the EC2 instance is provisioned, you will need to know the AMI ID before configuration. The AWS Command Line Interface (CLI) is used to list the available Red Hat Enterprise Linux (RHEL) image IDs. Prerequisites You have installed the AWS CLI. Procedure Use this command to list RHEL 8.4 Amazon Machine Images (AMI): USD aws ec2 describe-images --owners 309956199498 \ 1 --query 'sort_by(Images, &CreationDate)[*].[CreationDate,Name,ImageId]' \ 2 --filters "Name=name,Values=RHEL-8.4*" \ 3 --region us-east-1 \ 4 --output table 5 1 The --owners command option shows Red Hat images based on the account ID 309956199498 . Important This account ID is required to display AMI IDs for images that are provided by Red Hat. 2 The --query command option sets how the images are sorted with the parameters 'sort_by(Images, &CreationDate)[*].[CreationDate,Name,ImageId]' . In this case, the images are sorted by the creation date, and the table is structured to show the creation date, the name of the image, and the AMI IDs. 3 The --filter command option sets which version of RHEL is shown. In this example, since the filter is set by "Name=name,Values=RHEL-8.4*" , then RHEL 8.4 AMIs are shown. 4 The --region command option sets where the region where an AMI is stored. 5 The --output command option sets how the results are displayed. Note When creating a RHEL compute machine for AWS, ensure that the AMI is RHEL 8.4 or 8.5. Example output ------------------------------------------------------------------------------------------------------------ | DescribeImages | +---------------------------+-----------------------------------------------------+------------------------+ | 2021-03-18T14:23:11.000Z | RHEL-8.4.0_HVM_BETA-20210309-x86_64-1-Hourly2-GP2 | ami-07eeb4db5f7e5a8fb | | 2021-03-18T14:38:28.000Z | RHEL-8.4.0_HVM_BETA-20210309-arm64-1-Hourly2-GP2 | ami-069d22ec49577d4bf | | 2021-05-18T19:06:34.000Z | RHEL-8.4.0_HVM-20210504-arm64-2-Hourly2-GP2 | ami-01fc429821bf1f4b4 | | 2021-05-18T20:09:47.000Z | RHEL-8.4.0_HVM-20210504-x86_64-2-Hourly2-GP2 | ami-0b0af3577fe5e3532 | +---------------------------+-----------------------------------------------------+------------------------+ Additional resources You may also manually import RHEL images to AWS . 10.4. Preparing a RHEL compute node Before you add a Red Hat Enterprise Linux (RHEL) machine to your OpenShift Container Platform cluster, you must register each host with Red Hat Subscription Manager (RHSM), attach an active OpenShift Container Platform subscription, and enable the required repositories. On each host, register with RHSM: # subscription-manager register --username=<user_name> --password=<password> Pull the latest subscription data from RHSM: # subscription-manager refresh List the available subscriptions: # subscription-manager list --available --matches '*OpenShift*' In the output for the command, find the pool ID for an OpenShift Container Platform subscription and attach it: # subscription-manager attach --pool=<pool_id> Disable all yum repositories: Disable all the enabled RHSM repositories: # subscription-manager repos --disable="*" List the remaining yum repositories and note their names under repo id , if any: # yum repolist Use yum-config-manager to disable the remaining yum repositories: # yum-config-manager --disable <repo_id> Alternatively, disable all repositories: # yum-config-manager --disable \* Note that this might take a few minutes if you have a large number of available repositories Enable only the repositories required by OpenShift Container Platform 4.13: # subscription-manager repos \ --enable="rhel-8-for-x86_64-baseos-rpms" \ --enable="rhel-8-for-x86_64-appstream-rpms" \ --enable="rhocp-4.13-for-rhel-8-x86_64-rpms" \ --enable="fast-datapath-for-rhel-8-x86_64-rpms" Stop and disable firewalld on the host: # systemctl disable --now firewalld.service Note You must not enable firewalld later. If you do, you cannot access OpenShift Container Platform logs on the worker. 10.5. Attaching the role permissions to RHEL instance in AWS Using the Amazon IAM console in your browser, you may select the needed roles and assign them to a worker node. Procedure From the AWS IAM console, create your desired IAM role . Attach the IAM role to the desired worker node. Additional resources See Required AWS permissions for IAM roles . 10.6. Tagging a RHEL worker node as owned or shared A cluster uses the value of the kubernetes.io/cluster/<clusterid>,Value=(owned|shared) tag to determine the lifetime of the resources related to the AWS cluster. The owned tag value should be added if the resource should be destroyed as part of destroying the cluster. The shared tag value should be added if the resource continues to exist after the cluster has been destroyed. This tagging denotes that the cluster uses this resource, but there is a separate owner for the resource. Procedure With RHEL compute machines, the RHEL worker instance must be tagged with kubernetes.io/cluster/<clusterid>=owned or kubernetes.io/cluster/<cluster-id>=shared . Note Do not tag all existing security groups with the kubernetes.io/cluster/<name>,Value=<clusterid> tag, or the Elastic Load Balancing (ELB) will not be able to create a load balancer. 10.7. Adding more RHEL compute machines to your cluster You can add more compute machines that use Red Hat Enterprise Linux (RHEL) as the operating system to an OpenShift Container Platform 4.13 cluster. Prerequisites Your OpenShift Container Platform cluster already contains RHEL compute nodes. The hosts file that you used to add the first RHEL compute machines to your cluster is on the machine that you use the run the playbook. The machine that you run the playbook on must be able to access all of the RHEL hosts. You can use any method that your company allows, including a bastion with an SSH proxy or a VPN. The kubeconfig file for the cluster and the installation program that you used to install the cluster are on the machine that you use the run the playbook. You must prepare the RHEL hosts for installation. Configure a user on the machine that you run the playbook on that has SSH access to all of the RHEL hosts. If you use SSH key-based authentication, you must manage the key with an SSH agent. Install the OpenShift CLI ( oc ) on the machine that you run the playbook on. Procedure Open the Ansible inventory file at /<path>/inventory/hosts that defines your compute machine hosts and required variables. Rename the [new_workers] section of the file to [workers] . Add a [new_workers] section to the file and define the fully-qualified domain names for each new host. The file resembles the following example: In this example, the mycluster-rhel8-0.example.com and mycluster-rhel8-1.example.com machines are in the cluster and you add the mycluster-rhel8-2.example.com and mycluster-rhel8-3.example.com machines. Navigate to the Ansible playbook directory: USD cd /usr/share/ansible/openshift-ansible Run the scaleup playbook: USD ansible-playbook -i /<path>/inventory/hosts playbooks/scaleup.yml 1 1 For <path> , specify the path to the Ansible inventory file that you created. 10.8. Approving the certificate signing requests for your machines When you add machines to a cluster, two pending certificate signing requests (CSRs) are generated for each machine that you added. You must confirm that these CSRs are approved or, if necessary, approve them yourself. The client requests must be approved first, followed by the server requests. Prerequisites You added machines to your cluster. Procedure Confirm that the cluster recognizes the machines: USD oc get nodes Example output NAME STATUS ROLES AGE VERSION master-0 Ready master 63m v1.26.0 master-1 Ready master 63m v1.26.0 master-2 Ready master 64m v1.26.0 The output lists all of the machines that you created. Note The preceding output might not include the compute nodes, also known as worker nodes, until some CSRs are approved. Review the pending CSRs and ensure that you see the client requests with the Pending or Approved status for each machine that you added to the cluster: USD oc get csr Example output NAME AGE REQUESTOR CONDITION csr-8b2br 15m system:serviceaccount:openshift-machine-config-operator:node-bootstrapper Pending csr-8vnps 15m system:serviceaccount:openshift-machine-config-operator:node-bootstrapper Pending ... In this example, two machines are joining the cluster. You might see more approved CSRs in the list. If the CSRs were not approved, after all of the pending CSRs for the machines you added are in Pending status, approve the CSRs for your cluster machines: Note Because the CSRs rotate automatically, approve your CSRs within an hour of adding the machines to the cluster. If you do not approve them within an hour, the certificates will rotate, and more than two certificates will be present for each node. You must approve all of these certificates. After the client CSR is approved, the Kubelet creates a secondary CSR for the serving certificate, which requires manual approval. Then, subsequent serving certificate renewal requests are automatically approved by the machine-approver if the Kubelet requests a new certificate with identical parameters. Note For clusters running on platforms that are not machine API enabled, such as bare metal and other user-provisioned infrastructure, you must implement a method of automatically approving the kubelet serving certificate requests (CSRs). If a request is not approved, then the oc exec , oc rsh , and oc logs commands cannot succeed, because a serving certificate is required when the API server connects to the kubelet. Any operation that contacts the Kubelet endpoint requires this certificate approval to be in place. The method must watch for new CSRs, confirm that the CSR was submitted by the node-bootstrapper service account in the system:node or system:admin groups, and confirm the identity of the node. To approve them individually, run the following command for each valid CSR: USD oc adm certificate approve <csr_name> 1 1 <csr_name> is the name of a CSR from the list of current CSRs. To approve all pending CSRs, run the following command: USD oc get csr -o go-template='{{range .items}}{{if not .status}}{{.metadata.name}}{{"\n"}}{{end}}{{end}}' | xargs --no-run-if-empty oc adm certificate approve Note Some Operators might not become available until some CSRs are approved. Now that your client requests are approved, you must review the server requests for each machine that you added to the cluster: USD oc get csr Example output NAME AGE REQUESTOR CONDITION csr-bfd72 5m26s system:node:ip-10-0-50-126.us-east-2.compute.internal Pending csr-c57lv 5m26s system:node:ip-10-0-95-157.us-east-2.compute.internal Pending ... If the remaining CSRs are not approved, and are in the Pending status, approve the CSRs for your cluster machines: To approve them individually, run the following command for each valid CSR: USD oc adm certificate approve <csr_name> 1 1 <csr_name> is the name of a CSR from the list of current CSRs. To approve all pending CSRs, run the following command: USD oc get csr -o go-template='{{range .items}}{{if not .status}}{{.metadata.name}}{{"\n"}}{{end}}{{end}}' | xargs oc adm certificate approve After all client and server CSRs have been approved, the machines have the Ready status. Verify this by running the following command: USD oc get nodes Example output NAME STATUS ROLES AGE VERSION master-0 Ready master 73m v1.26.0 master-1 Ready master 73m v1.26.0 master-2 Ready master 74m v1.26.0 worker-0 Ready worker 11m v1.26.0 worker-1 Ready worker 11m v1.26.0 Note It can take a few minutes after approval of the server CSRs for the machines to transition to the Ready status. Additional information For more information on CSRs, see Certificate Signing Requests . 10.9. Required parameters for the Ansible hosts file You must define the following parameters in the Ansible hosts file before you add Red Hat Enterprise Linux (RHEL) compute machines to your cluster. Parameter Description Values ansible_user The SSH user that allows SSH-based authentication without requiring a password. If you use SSH key-based authentication, then you must manage the key with an SSH agent. A user name on the system. The default value is root . ansible_become If the values of ansible_user is not root, you must set ansible_become to True , and the user that you specify as the ansible_user must be configured for passwordless sudo access. True . If the value is not True , do not specify and define this parameter. openshift_kubeconfig_path Specifies a path and file name to a local directory that contains the kubeconfig file for your cluster. The path and name of the configuration file.

Commands:
aws ec2 describe-images --owners 309956199498 \ 1 --query 'sort_by(Images, &CreationDate)[*].[CreationDate,Name,ImageId]' \ 2 --filters "Name=name,Values=RHEL-8.4*" \ 3 --region us-east-1 \ 4 --output table 5
------------------------------------------------------------------------------------------------------------ | DescribeImages | +---------------------------+-----------------------------------------------------+------------------------+ | 2021-03-18T14:23:11.000Z | RHEL-8.4.0_HVM_BETA-20210309-x86_64-1-Hourly2-GP2 | ami-07eeb4db5f7e5a8fb | | 2021-03-18T14:38:28.000Z | RHEL-8.4.0_HVM_BETA-20210309-arm64-1-Hourly2-GP2 | ami-069d22ec49577d4bf | | 2021-05-18T19:06:34.000Z | RHEL-8.4.0_HVM-20210504-arm64-2-Hourly2-GP2 | ami-01fc429821bf1f4b4 | | 2021-05-18T20:09:47.000Z | RHEL-8.4.0_HVM-20210504-x86_64-2-Hourly2-GP2 | ami-0b0af3577fe5e3532 | +---------------------------+-----------------------------------------------------+------------------------+
subscription-manager register --username=<user_name> --password=<password>
subscription-manager refresh
subscription-manager list --available --matches '*OpenShift*'
subscription-manager attach --pool=<pool_id>
subscription-manager repos --disable="*"
yum repolist
yum-config-manager --disable <repo_id>
yum-config-manager --disable \*
subscription-manager repos --enable="rhel-8-for-x86_64-baseos-rpms" --enable="rhel-8-for-x86_64-appstream-rpms" --enable="rhocp-4.13-for-rhel-8-x86_64-rpms" --enable="fast-datapath-for-rhel-8-x86_64-rpms"
systemctl disable --now firewalld.service
[all:vars] ansible_user=root #ansible_become=True openshift_kubeconfig_path="~/.kube/config" [workers] mycluster-rhel8-0.example.com mycluster-rhel8-1.example.com [new_workers] mycluster-rhel8-2.example.com mycluster-rhel8-3.example.com
cd /usr/share/ansible/openshift-ansible
ansible-playbook -i /<path>/inventory/hosts playbooks/scaleup.yml 1
oc get nodes
NAME STATUS ROLES AGE VERSION master-0 Ready master 63m v1.26.0 master-1 Ready master 63m v1.26.0 master-2 Ready master 64m v1.26.0
oc get csr
NAME AGE REQUESTOR CONDITION csr-8b2br 15m system:serviceaccount:openshift-machine-config-operator:node-bootstrapper Pending csr-8vnps 15m system:serviceaccount:openshift-machine-config-operator:node-bootstrapper Pending
oc adm certificate approve <csr_name> 1
oc get csr -o go-template='{{range .items}}{{if not .status}}{{.metadata.name}}{{"\n"}}{{end}}{{end}}' | xargs --no-run-if-empty oc adm certificate approve
oc get csr
NAME AGE REQUESTOR CONDITION csr-bfd72 5m26s system:node:ip-10-0-50-126.us-east-2.compute.internal Pending csr-c57lv 5m26s system:node:ip-10-0-95-157.us-east-2.compute.internal Pending
oc adm certificate approve <csr_name> 1
oc get csr -o go-template='{{range .items}}{{if not .status}}{{.metadata.name}}{{"\n"}}{{end}}{{end}}' | xargs oc adm certificate approve
oc get nodes
NAME STATUS ROLES AGE VERSION master-0 Ready master 73m v1.26.0 master-1 Ready master 73m v1.26.0 master-2 Ready master 74m v1.26.0 worker-0 Ready worker 11m v1.26.0 worker-1 Ready worker 11m v1.26.0