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Chapter 8. Updating a cluster that includes RHEL compute machines

You can update, or upgrade, an OpenShift Container Platform cluster. If your cluster contains Red Hat Enterprise Linux (RHEL) machines, you must perform more steps to update those machines.

8.1. Prerequisites

Important

If you are running cluster monitoring with an attached PVC for Prometheus, you might experience OOM kills during cluster update. When persistent storage is in use for Prometheus, Prometheus memory usage doubles during cluster update and for several hours after update is complete. To avoid the OOM kill issue, allow worker nodes with double the size of memory that was available prior to the update. For example, if you are running monitoring on the minimum recommended nodes, which is 2 cores with 8 GB of RAM, increase memory to 16 GB. For more information, see BZ#1925061.

Additional resources

8.2. Updating a cluster by using the web console

If updates are available, you can update your cluster from the web console.

You can find information about available OpenShift Container Platform advisories and updates in the errata section of the Customer Portal.

Prerequisites

  • Have access to the web console as a user with admin privileges.

Procedure

  1. From the web console, click Administration Cluster Settings and review the contents of the Details tab.

  2. For production clusters, ensure that the Channel is set to the correct channel for the version that you want to update to, such as stable-4.7.

    Important

    For production clusters, you must subscribe to a stable-* or fast-* channel.

    • If the Update status is not Updates available, you cannot update your cluster.
    • Select channel indicates the cluster version that your cluster is running or is updating to.

  3. Select a version to update to, and click Save.

    The Input channel Update status changes to Update to <product-version> in progress, and you can review the progress of the cluster update by watching the progress bars for the Operators and nodes.

    Note

    If you are upgrading your cluster to the next minor version, like version 4.y to 4.(y+1), it is recommended to confirm your nodes are updated before deploying workloads that rely on a new feature. Any pools with worker nodes that are not yet updated are displayed on the Cluster Settings page.

  4. After the update completes and the Cluster Version Operator refreshes the available updates, check if more updates are available in your current channel.

    • If updates are available, continue to perform updates in the current channel until you can no longer update.
    • If no updates are available, change the Channel to the stable-* or fast-* channel for the next minor version, and update to the version that you want in that channel.

    You might need to perform several intermediate updates until you reach the version that you want.

    Note

    When you update a cluster that contains Red Hat Enterprise Linux (RHEL) worker machines, those workers temporarily become unavailable during the update process. You must run the update playbook against each RHEL machine as it enters the NotReady state for the cluster to finish updating.

8.3. Optional: Adding hooks to perform Ansible tasks on RHEL machines

You can use hooks to run Ansible tasks on the RHEL compute machines during the OpenShift Container Platform update.

8.3.1. About Ansible hooks for upgrades

When you update OpenShift Container Platform, you can run custom tasks on your Red Hat Enterprise Linux (RHEL) nodes during specific operations by using hooks. Hooks allow you to provide files that define tasks to run before or after specific update tasks. You can use hooks to validate or modify custom infrastructure when you update the RHEL compute nodes in you OpenShift Container Platform cluster.

Because when a hook fails, the operation fails, you must design hooks that are idempotent, or can run multiple times and provide the same results.

Hooks have the following important limitations: - Hooks do not have a defined or versioned interface. They can use internal openshift-ansible variables, but it is possible that the variables will be modified or removed in future OpenShift Container Platform releases. - Hooks do not have error handling, so an error in a hook halts the update process. If you get an error, you must address the problem and then start the upgrade again.

8.3.2. Configuring the Ansible inventory file to use hooks

You define the hooks to use when you update the Red Hat Enterprise Linux (RHEL) compute machines, which are also known as worker machines, in the hosts inventory file under the all:vars section.

Prerequisites

  • You have access to the machine that you used to add the RHEL compute machines cluster. You must have access to the hosts Ansible inventory file that defines your RHEL machines.

Procedure

  1. After you design the hook, create a YAML file that defines the Ansible tasks for it. This file must be a set of tasks and cannot be a playbook, as shown in the following example: 

    ---
# Trivial example forcing an operator to acknowledge the start of an upgrade
# file=/home/user/openshift-ansible/hooks/pre_compute.yml

- name: note the start of a compute machine update
  debug:
      msg: "Compute machine upgrade of {{ inventory_hostname }} is about to start"

- name: require the user agree to start an upgrade
  pause:
      prompt: "Press Enter to start the compute machine update"

  2. Modify the hosts Ansible inventory file to specify the hook files. The hook files are specified as parameter values in the [all:vars] section, as shown:

    Example hook definitions in an inventory file

    [all:vars]
openshift_node_pre_upgrade_hook=/home/user/openshift-ansible/hooks/pre_node.yml
openshift_node_post_upgrade_hook=/home/user/openshift-ansible/hooks/post_node.yml

    To avoid ambiguity in the paths to the hook, use absolute paths instead of a relative paths in their definitions.

8.3.3. Available hooks for RHEL compute machines

You can use the following hooks when you update the Red Hat Enterprise Linux (RHEL) compute machines in your OpenShift Container Platform cluster.

Hook nameDescription

openshift_node_pre_cordon_hook

  • Runs before each node is cordoned.
  • This hook runs against each node in serial.
  • If a task must run against a different host, the task must use delegate_to or local_action.

openshift_node_pre_upgrade_hook

  • Runs after each node is cordoned but before it is updated.
  • This hook runs against each node in serial.
  • If a task must run against a different host, the task must use delegate_to or local_action.

openshift_node_pre_uncordon_hook

  • Runs after each node is updated but before it is uncordoned.
  • This hook runs against each node in serial.
  • If a task must run against a different host, they task must use delegate_to or local_action.

openshift_node_post_upgrade_hook

  • Runs after each node uncordoned. It is the last node update action.
  • This hook runs against each node in serial.
  • If a task must run against a different host, the task must use delegate_to or local_action.

8.4. Updating RHEL compute machines in your cluster

After you update your cluster, you must update the Red Hat Enterprise Linux (RHEL) compute machines in your cluster.

Important

Because only Red Hat Enterprise Linux (RHEL) version 7.9 or later is supported for worker (compute) machines, you must not upgrade the RHEL worker machines to version 8.

You can also update your compute machines to another minor version of OpenShift Container Platform if you are using RHEL as the operating system. You do not need to exclude any RPM packages from RHEL when performing a minor version update.

Prerequisites

  • You updated your cluster.

    Important

    Because the RHEL machines require assets that are generated by the cluster to complete the update process, you must update the cluster before you update the RHEL worker machines in it.

  • You have access to the local machine that you used to add the RHEL compute machines to your cluster. You must have access to the hosts Ansible inventory file that defines your RHEL machines and the upgrade playbook.
  • For updates to a minor version, the RPM repository is using the same version of OpenShift Container Platform that is running on your cluster.

Procedure

  1. Stop and disable firewalld on the host: 

    # systemctl disable --now firewalld.service
    Note

    By default, the base OS RHEL with "Minimal" installation option enables firewalld serivce. Having the firewalld service enabled on your host prevents you from accessing OpenShift Container Platform logs on the worker. Do not enable firewalld later if you wish to continue accessing OpenShift Container Platform logs on the worker.

  2. Enable the repositories that are required for OpenShift Container Platform 4.7:

    1. On the machine that you run the Ansible playbooks, update the required repositories: 

      # subscription-manager repos --disable=rhel-7-server-ose-4.6-rpms \
                             --enable=rhel-7-server-ansible-2.9-rpms \
                             --enable=rhel-7-server-ose-4.7-rpms

    2. On the machine that you run the Ansible playbooks, update the required packages, including openshift-ansible: 

      # yum update openshift-ansible openshift-clients

    3. On each RHEL compute node, update the required repositories: 

      # subscription-manager repos --disable=rhel-7-server-ose-4.6-rpms \
                             --enable=rhel-7-server-ose-4.7-rpms  \
                             --enable=rhel-7-fast-datapath-rpms   \
                             --enable=rhel-7-server-optional-rpms

  3. Update a RHEL worker machine:

    1. Review the current node status to determine which RHEL worker to update: 

      # oc get node

      Example output

      NAME                        STATUS                        ROLES    AGE    VERSION
mycluster-control-plane-0   Ready                         master   145m   v1.20.0
mycluster-control-plane-1   Ready                         master   145m   v1.20.0
mycluster-control-plane-2   Ready                         master   145m   v1.20.0
mycluster-rhel7-0           NotReady,SchedulingDisabled   worker   98m    v1.14.6+97c81d00e
mycluster-rhel7-1           Ready                         worker   98m    v1.14.6+97c81d00e
mycluster-rhel7-2           Ready                         worker   98m    v1.14.6+97c81d00e
mycluster-rhel7-3           Ready                         worker   98m    v1.14.6+97c81d00e

      Note which machine has the NotReady,SchedulingDisabled status.

    2. Review your Ansible inventory file at /<path>/inventory/hosts and update its contents so that only the machine with the NotReady,SchedulingDisabled status is listed in the [workers] section, as shown in the following example: 

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

openshift_kubeconfig_path="~/.kube/config"

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

    3. Change to the openshift-ansible directory: 

      $ cd /usr/share/ansible/openshift-ansible

    4. Run the upgrade playbook: 

      $ ansible-playbook -i /<path>/inventory/hosts playbooks/upgrade.yml 1
      1
      For <path>, specify the path to the Ansible inventory file that you created.
      Note

      The upgrade playbook only upgrades the OpenShift Container Platform packages. It does not update the operating system packages.

  4. Follow the process in the previous step to update each RHEL worker machine in your cluster.

  5. After you update all of the workers, confirm that all of your cluster nodes have updated to the new version: 

    # oc get node

    Example output

    NAME                        STATUS                        ROLES    AGE    VERSION
mycluster-control-plane-0   Ready                         master   145m   v1.20.0
mycluster-control-plane-1   Ready                         master   145m   v1.20.0
mycluster-control-plane-2   Ready                         master   145m   v1.20.0
mycluster-rhel7-0           NotReady,SchedulingDisabled   worker   98m    v1.20.0
mycluster-rhel7-1           Ready                         worker   98m    v1.20.0
mycluster-rhel7-2           Ready                         worker   98m    v1.20.0
mycluster-rhel7-3           Ready                         worker   98m    v1.20.0

  6. Optional: Update the operating system packages that were not updated by the upgrade playbook. To update packages that are not on 4.7, use the following command: 

    # yum update
    Note

    You do not need to exclude RPM packages if you are using the same RPM repository that you used when you installed 4.7.

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