Before performing your migration to OKD 4.4, it is important to take the time to properly plan for the transition. OKD 4 introduces architectural changes and enhancements, so the procedures that you used to manage your OKD 3 cluster might not apply for OKD 4.
This planning document assumes that you are transitioning from OKD 3.11 to OKD 4.4.
This document provides high-level information on the most important differences between OKD 3 and OKD 4 and the most noteworthy migration considerations. For detailed information on configuring your OKD 4 cluster, review the appropriate sections of the OKD documentation. For detailed information on new features and other notable technical changes, review the OpenShift Container Platform 4.4 release notes.
It is not possible to upgrade your existing OKD 3 cluster to OKD 4. You must start with a new OKD 4 installation. Tools are available to assist in migrating your control plane settings and application workloads.
With OKD 3, administrators individually deployed Red Hat Enterprise Linux (RHEL) hosts, and then installed OKD on top of these hosts to form a cluster. Administrators were responsible for properly configuring these hosts and performing updates.
OKD 4 represents a significant change in the way that OKD clusters are deployed and managed. OKD 4 includes new technologies and functionality, such as Operators, MachineSets, and Red Hat Enterprise Linux CoreOS (RHCOS), which are core to the operation of the cluster. This technology shift enables clusters to self-manage some functions previously performed by administrators. This also ensures platform stability and consistency, and simplifies installation and scaling.
For more information, see OpenShift Container Platform architecture.
OKD 4 uses Red Hat Enterprise Linux CoreOS (RHCOS), which is designed to run containerized applications, and provides efficient installation, Operator-based management, and simplified upgrades. RHCOS is an immutable container host, rather than a customizable operating system like RHEL. RHCOS enables OKD 4 to manage and automate the deployment of the underlying container host. RHCOS is a part of OKD, which means that everything runs inside a container and is deployed using OKD.
In OKD 4, control plane nodes must run RHCOS, ensuring that full-stack automation is maintained for the control plane. This makes rolling out updates and upgrades a much easier process than in OKD 3.
For more information, see Red Hat Enterprise Linux CoreOS.
Operators are a method of packaging, deploying, and managing a Kubernetes application. Operators ease the operational complexity of running another piece of software. They watch over your environment and use the current state to make decisions in real time. Advanced Operators are designed to upgrade and react to failures automatically.
For more information, see Understanding Operators.
To install OKD 3.11, you prepared your Red Hat Enterprise Linux (RHEL) hosts, set all of the configuration values your cluster needed, and then ran an Ansible playbook to install and set up your cluster.
In OKD 4.4, you use the OpenShift installation program to create a minimum set of resources required for a cluster. Once the cluster is running, you use Operators to further configure your cluster and to install new services. After first boot, Red Hat Enterprise Linux CoreOS (RHCOS) systems are managed by the Machine Config Operator (MCO) that runs in the OKD cluster.
For more information, see Installation process.
If you want to add RHEL worker machines to your OKD 4.4 cluster, you use an Ansible playbook to join the RHEL worker machines after the cluster is running. For more information, see Adding RHEL compute machines to an OKD cluster.
In OKD 3.11, you installed your cluster on infrastructure that you prepared and maintained. In addition to providing your own infrastructure, OKD 4 offers an option to deploy a cluster on infrastructure that the OKD installation program provisions and the cluster maintains.
For more information, see OpenShift Container Platform installation overview.
In OKD 3.11, you upgraded your cluster by running Ansible playbooks. In OKD 4.4, the cluster manages its own updates, including updates to Red Hat Enterprise Linux CoreOS (RHCOS) on cluster nodes. You can easily upgrade your cluster by using the web console or by using the
oc adm upgrade command from the OpenShift CLI and the Operators will automatically upgrade themselves. If your OKD 4.4 cluster has Red Hat Enterprise Linux worker machines, then you will still need to run an Ansible playbook to upgrade those worker machines.
For more information, see Updating clusters.
Review the changes and other considerations that might affect your transition from OKD 3.11 to OKD 4.
Review the following storage changes to consider when transitioning from OKD 3.11 to OKD 4.4.
Local storage is only supported by using the Local Storage Operator in OKD 4.4. It is not supported to use the local provisioner method from OKD 3.11.
For more information, see Persistent storage using local volumes.
The FlexVolume plug-in location changed from OKD 3.11. The new location in OKD 4.4 is
/etc/kubernetes/kubelet-plugins/volume/exec. Attachable FlexVolume plug-ins are no longer supported.
For more information, see Persistent storage using FlexVolume.
Persistent storage using the Container Storage Interface (CSI) was Technology Preview in OKD 3.11. CSI version 1.1.0 is fully supported in OKD 4.4, but does not ship with any CSI drivers. You must install your own driver.
For more information, see Persistent storage using the Container Storage Interface (CSI).
Red Hat OpenShift Container Storage 3, which is available for use with OKD 3.11, uses Red Hat Gluster Storage as the backing storage.
Red Hat OpenShift Container Storage 4, which is available for use with OKD 4, uses Red Hat Ceph Storage as the backing storage.
For more information, see Persistent storage using Red Hat OpenShift Container Storage and the interoperability matrix article.
Support for the following persistent storage options from OKD 3.11 has changed in OKD 4.4:
GlusterFS is no longer supported.
CephFS as a standalone product is no longer supported.
Ceph RBD as a standalone product is no longer supported.
If you used of one these in OKD 3.11, you must choose a different persistent storage option for full support in OKD 4.4.
For more information, see Understanding persistent storage.
Review the following networking changes to consider when transitioning from OKD 3.11 to OKD 4.4.
The default network isolation mode for OKD 3.11 was
ovs-subnet, though users frequently switched to use
ovn-multitenant. The default network isolation mode for OKD 4.4 is now NetworkPolicy.
If your OKD 3.11 cluster used the
ovs-multitenant mode, it is recommended to switch to the NetworkPolicy mode for your OKD 4.4 cluster. NetworkPolicy is supported upstream, is more flexible, and also provides the functionality that
ovs-multitenant does. If you want to maintain the
ovs-multitenant behavior while using NetworkPolicy in OKD 4.4, follow the steps to configure multitenant isolation using NetworkPolicy.
For more information, see About network policy.
In OKD 3.11, you could use IPsec to encrypt traffic between hosts. OKD 4.4 does not support IPsec. It is recommended to use Red Hat OpenShift Service Mesh to enable mutual TLS between services.
For more information, see Understanding Red Hat OpenShift Service Mesh.
Review the following logging changes to consider when transitioning from OKD 3.11 to OKD 4.4.
OKD 4 provides a simple deployment mechanism for cluster logging, by using a Cluster Logging custom resource. Once deployed, the cluster logging experience is the same as it was in OKD 3.11.
For more information, see About deploying and configuring cluster logging.
You cannot transition your aggregate logging data from OKD 3.11 into your new OKD 4 cluster.
For more information, see About cluster logging.
Review the following security changes to consider when transitioning from OKD 3.11 to OKD 4.4.
In OKD 3.11, an unauthenticated user could access the discovery endpoints (for example,
/apis/*). For security reasons, unauthenticated access to the discovery endpoints is no longer allowed in OKD 4.4. If you do need to allow unauthenticated access, you can configure the RBAC settings as necessary; however, be sure to consider the security implications as this can expose internal cluster components to the external network.
Configuration for identity providers has changed for OKD 4, including the following notable changes:
The request header identity provider in OKD 4.4 requires mutual TLS, where in OKD 3.11 it did not.
The configuration of the OpenID Connect identity provider was simplified in OKD 4.4. It now obtains data, which previously had to specified in OKD 3.11, from the provider’s
For more information, see Understanding identity provider configuration.
Review the following monitoring changes to consider when transitioning from OKD 3.11 to OKD 4.4.
The default alert that triggers to ensure the availability of the monitoring structure was called
DeadMansSwitch in OKD 3.11. This was renamed to
Watchdog in OKD 4. If you had PagerDuty integration set up with this alert in OKD 3.11, you must set up the PagerDuty integration for the
Watchdog alert in OKD 4.
For more information, see Applying custom Alertmanager configuration.