Chapter 1. Upgrade Methods and Strategies
1.1. Introduction to Upgrading Clusters
When new versions of OpenShift Container Platform are released, you can upgrade your existing cluster to apply the latest enhancements and bug fixes. This includes upgrading from previous minor versions, such as release 3.7 to 3.9, and applying asynchronous errata updates within a minor version (3.9.z releases). See the OpenShift Container Platform 3.9 Release Notes to review the latest changes.
Due to the core architectural changes between the major versions, OpenShift Enterprise 2 environments cannot be upgraded to OpenShift Container Platform 3 and require a fresh installation.
Unless noted otherwise, node and masters within a major version are forward and backward compatible across one minor version, so upgrading your cluster should go smoothly. However, you should not run mismatched versions longer than necessary to upgrade the entire cluster.
Before upgrading, ensure that all OpenShift Container Platform services are running well.
In the event of a control plane upgrade failure, check the versions of your masters to ensure that all versions are the same. If your masters are all the same version, re-run the upgrade. If they differ, downgrade the masters to match the lower versioned master, then re-run the upgrade.
The OpenShift Container Platform 3.9 release includes a merge of features and fixes from Kubernetes 1.8 and 1.9. As a result, the upgrade process from OpenShift Container Platform 3.7 completes with the cluster fully upgraded to OpenShift Container Platform 3.9, seemingly "skipping" the 3.8 release. Technically, the OpenShift Container Platform 3.7 cluster is first upgraded to 3.8-versioned packages, and then the process immediately continues upgrading to OpenShift Container Platform 3.9 automatically. Your cluster should only remain at 3.8-versioned packages for as long as it takes to successfully complete the upgrade to OpenShift Container Platform 3.9.
1.2. Upgrade Methods
There are two methods available for performing OpenShift Container Platform cluster upgrades: automated or manual.
1.2.1. Automated Method
The automated upgrade method uses Ansible playbooks to automate the tasks needed to upgrade a OpenShift Container Platform cluster. You should use the inventory file that you used during initial installation or during the last time that the upgrade was successful to run the upgrade playbook. Using this method allows you to choose between either upgrade strategy: in-place upgrades or blue-green deployments.
1.2.2. Manual Method
The manual upgrade method breaks down the steps that happen during an automated Ansible-based upgrade and provides the equivalent commands to run manually. Using this method describes the in-place upgrade strategy.
1.3. Upgrade Strategies
When using the automated upgrade method, there are two strategies you can take for performing the OpenShift Container Platform cluster upgrade: in-place upgrades or blue-green deployments. When using the manual upgrade method, an in-place upgrade is described.
1.3.1. In-place Upgrades
With in-place upgrades, the cluster upgrade is performed on all hosts in a single, running cluster: first masters and then nodes. Pods are evacuated off of nodes and recreated on other running nodes before a node upgrade begins; this helps reduce downtime of user applications.
If you installed using the quick or advanced installation, you can perform an automated in-place upgrade. Alternatively, you can upgrade in-place manually.
Quick Installation is now deprecated in OpenShift Container Platform 3.9 and will be completely removed in a future release.
Quick installation will only be capable of installing 3.9. It will not be able to upgrade from 3.7 or 3.8 to 3.9.
1.3.2. Blue-green Deployments
The blue-green deployment upgrade method follows a similar flow to the in-place method: masters and etcd servers are still upgraded first, however a parallel environment is created for new nodes instead of upgrading them in-place.
This method allows administrators to switch traffic from the old set of nodes (e.g., the "blue" deployment) to the new set (e.g., the "green" deployment) after the new deployment has been verified. If a problem is detected, it is also then easy to rollback to the old deployment quickly.
