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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.

About adding RHEL compute nodes to a cluster

In OpenShift Container Platform 4.4, you have the option of using Red Hat Enterprise Linux (RHEL) machines as compute machines, which are also known as worker machines, in your cluster if you use a user-provisioned infrastructure installation. You must use Red Hat Enterprise Linux CoreOS (RHCOS) machines for the control plane, or master, machines in your cluster.

As with all installations that use user-provisioned infrastructure, if you choose to use RHEL compute machines in your cluster, you take responsibility for all operating system life cycle management and maintenance, including performing system updates, applying patches, and completing 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, which are also known as worker 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 percent 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 7.6-7.8 with "Minimal" installation option.

      Only RHEL 7.6-7.8 is supported in OpenShift Container Platform 4.4. You must not upgrade your compute machines to RHEL 8.

    • If you deployed OpenShift Container Platform in FIPS mode, you must enable FIPS on the RHEL machine before you boot it. See Enabling FIPS Mode in the RHEL 7 documentation.

    • 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 the system’s temporary directory. The system’s temporary directory is determined according to the rules defined in the tempfile module in Python’s 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 host names. Any network security access control that is in place must allow the system access to the cluster’s API service endpoints.

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 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 4.4:

    # subscription-manager repos \
    --enable="rhel-7-server-rpms" \
    --enable="rhel-7-server-extras-rpms" \
    --enable="rhel-7-server-ose-4.4-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.

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 4.4 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

  1. Open the Ansible inventory file at /<path>/inventory/hosts that defines your compute machine hosts and required variables.

  2. Rename the [new_workers] section of the file to [workers].

  3. 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:

    [all:vars]
ansible_user=root
#ansible_become=True

openshift_kubeconfig_path="~/.kube/config"

[workers]
mycluster-rhel7-0.example.com
mycluster-rhel7-1.example.com

[new_workers]
mycluster-rhel7-2.example.com
mycluster-rhel7-3.example.com

    In this example, the mycluster-rhel7-0.example.com and mycluster-rhel7-1.example.com machines are in the cluster and you add the mycluster-rhel7-2.example.com and mycluster-rhel7-3.example.com machines.

  4. Run the scaleup playbook:

    $ cd /usr/share/ansible/openshift-ansible
$ ansible-playbook -i /<path>/inventory/hosts playbooks/scaleup.yml (1)
    1 For <path>, specify the path to the Ansible inventory file that you created.

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

  1. Confirm that the cluster recognizes the machines:

    # oc get nodes

NAME                    STATUS   ROLES    AGE   VERSION
master-01.example.com   Ready    master   40d   v1.17.1
master-02.example.com   Ready    master   40d   v1.17.1
master-03.example.com   Ready    master   40d   v1.17.1
worker-01.example.com   Ready    worker   40d   v1.17.1
worker-02.example.com   Ready    worker   40d   v1.17.1

    The output lists all of the machines that you created.

  2. 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:

    $ 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
...

    In this example, two machines are joining the cluster. You might see more approved CSRs in the list.

  3. 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:

    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 you approve the initial CSRs, the subsequent node client CSRs are automatically approved by the cluster kube-controller-manager. You must implement a method of automatically approving the kubelet serving certificate requests.

    • To approve them individually, run the following command for each valid CSR:

      $ 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:

      $ oc get csr -o go-template='{{range .items}}{{if not .status}}{{.metadata.name}}{{"\n"}}{{end}}{{end}}' | xargs oc adm certificate approve

  4. Now that your client requests are approved, you must review the server requests for each machine that you added to the cluster:

    $ 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
...

  5. 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:

      $ 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:

      $ oc get csr -o go-template='{{range .items}}{{if not .status}}{{.metadata.name}}{{"\n"}}{{end}}{{end}}' | xargs oc adm certificate approve

  6. After all client and server CSRs have been approved, the machines have the Ready status. Verify this by running the following command:

    $ oc get nodes
    Example output
    NAME      STATUS    ROLES   AGE  VERSION
master-0  Ready     master  73m  v1.20.0
master-1  Ready     master  73m  v1.20.0
master-2  Ready     master  74m  v1.20.0
worker-0  Ready     worker  11m  v1.20.0
worker-1  Ready     worker  11m  v1.20.0

    It can take a few minutes after approval of the server CSRs for the machines to transition to the Ready status.
Additional information

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.

Paramter 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.