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About adding RHEL compute nodes to a cluster

In OpenShift Container Platform 4.11, you have the option of using Red Hat Enterprise Linux (RHEL) machines as compute machines in your cluster if you use a user-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.

  • 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.

You must add any RHEL compute machines to the cluster after you initialize the control plane.

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 8.5 to 8.7 with "Minimal" installation option.

      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.

    • If you deployed OpenShift Container Platform in FIPS mode, you must enable FIPS on the RHEL machine before you boot it. See Installing a RHEL 8 system with FIPS mode enabled in the RHEL 8 documentation.

The use of FIPS Validated / Modules in Process cryptographic libraries is only supported on OpenShift Container Platform deployments on the x86_64 architecture.

  • 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

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.

Preparing an image for your cloud

Amazon Machine Images (AMI) are required because 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 will need a valid AMI ID so that the correct RHEL version needed for the compute machines is selected.

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):

    $ 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.

    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.

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

Preparing the machine to run the playbook

Before you can add compute machines that use Red Hat Enterprise Linux (RHEL) as the operating system to an OpenShift Container Platform 4.11 cluster, you must prepare a RHEL 8 machine to run an Ansible playbook that adds the new node to the cluster. This machine is not part of the cluster but must be able to access it.

Prerequisites
  • Install the OpenShift CLI (oc) on the machine that you run the playbook on.

  • Log in as a user with cluster-admin permission.

Procedure
  1. Ensure that the kubeconfig file for the cluster and the installation program that you used to install the cluster are on the RHEL 8 machine. One way to accomplish this is to use the same machine that you used to install the cluster.

  2. Configure the machine to access all of the RHEL hosts that you plan to use as compute machines. You can use any method that your company allows, including a bastion with an SSH proxy or a VPN.

  3. 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.

  4. If you have not already done so, register the machine with RHSM and attach a pool with an OpenShift subscription to it:

    1. Register the machine with RHSM:

      # subscription-manager register --username=<user_name> --password=<password>
    2. Pull the latest subscription data from RHSM:

      # subscription-manager refresh
    3. List the available subscriptions:

      # subscription-manager list --available --matches '*OpenShift*'
    4. In the output for the previous command, find the pool ID for an OpenShift Container Platform subscription and attach it:

      # subscription-manager attach --pool=<pool_id>
  5. Enable the repositories required by OpenShift Container Platform 4.11:

    # subscription-manager repos \
        --enable="rhel-8-for-x86_64-baseos-rpms" \
        --enable="rhel-8-for-x86_64-appstream-rpms" \
        --enable="rhocp-4.11-for-rhel-8-x86_64-rpms"
  6. Install the required packages, including openshift-ansible:

    # yum install openshift-ansible openshift-clients jq

    The openshift-ansible package provides installation program utilities and pulls in other packages that you require to add a RHEL compute node to your cluster, such as Ansible, playbooks, and related configuration files. The openshift-clients provides the oc CLI, and the jq package improves the display of JSON output on your command line.

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.

  1. On each host, register with RHSM:

    # subscription-manager register --username=<user_name> --password=<password>
  2. Pull the latest subscription data from RHSM:

    # subscription-manager refresh
  3. List the available subscriptions:

    # subscription-manager list --available --matches '*OpenShift*'
  4. In the output for the previous command, find the pool ID for an OpenShift Container Platform subscription and attach it:

    # subscription-manager attach --pool=<pool_id>
  5. Disable all yum repositories:

    1. Disable all the enabled RHSM repositories:

      # subscription-manager repos --disable="*"
    2. List the remaining yum repositories and note their names under repo id, if any:

      # yum repolist
    3. 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

  6. Enable only the repositories required by OpenShift Container Platform 4.11:

    # subscription-manager repos \
        --enable="rhel-8-for-x86_64-baseos-rpms" \
        --enable="rhel-8-for-x86_64-appstream-rpms" \
        --enable="rhocp-4.11-for-rhel-8-x86_64-rpms" \
        --enable="fast-datapath-for-rhel-8-x86_64-rpms"
  7. Stop and disable firewalld on the host:

    # systemctl disable --now firewalld.service

    You must not enable firewalld later. If you do, you cannot access OpenShift Container Platform logs on the worker.

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
  1. From the AWS IAM console, create your desired IAM role.

  2. Attach the IAM role to the desired worker node.

Additional resources

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.

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.

Adding a RHEL compute machine to your cluster

You can add compute machines that use Red Hat Enterprise Linux as the operating system to an OpenShift Container Platform 4.11 cluster.

Prerequisites
  • You installed the required packages and performed the necessary configuration on the machine that you run the playbook on.

  • You prepared the RHEL hosts for installation.

Procedure

Perform the following steps on the machine that you prepared to run the playbook:

  1. Create an Ansible inventory file that is named /<path>/inventory/hosts that defines your compute machine hosts and required variables:

    [all:vars]
    ansible_user=root (1)
    #ansible_become=True (2)
    
    openshift_kubeconfig_path="~/.kube/config" (3)
    
    [new_workers] (4)
    mycluster-rhel8-0.example.com
    mycluster-rhel8-1.example.com
    1 Specify the user name that runs the Ansible tasks on the remote compute machines.
    2 If you do not specify root for the ansible_user, you must set ansible_become to True and assign the user sudo permissions.
    3 Specify the path and file name of the kubeconfig file for your cluster.
    4 List each RHEL machine to add to your cluster. You must provide the fully-qualified domain name for each host. This name is the hostname that the cluster uses to access the machine, so set the c