Chapter 1. Migration from OpenShift Container Platform 3 to 4 overview OpenShift Container Platform 4 clusters are different from OpenShift Container Platform 3 clusters. OpenShift Container Platform 4 clusters contain new technologies and functionality that result in a cluster that is self-managing, flexible, and automated. To learn more about migrating from OpenShift Container Platform 3 to 4 see About migrating from OpenShift Container Platform 3 to 4 . 1.1. Differences between OpenShift Container Platform 3 and 4 Before migrating from OpenShift Container Platform 3 to 4, you can check differences between OpenShift Container Platform 3 and 4 . Review the following information: Architecture Installation and update Storage , network , logging , security , and monitoring considerations 1.2. Planning network considerations Before migrating from OpenShift Container Platform 3 to 4, review the differences between OpenShift Container Platform 3 and 4 for information about the following areas: DNS considerations Isolating the DNS domain of the target cluster from the clients . Setting up the target cluster to accept the source DNS domain . You can migrate stateful application workloads from OpenShift Container Platform 3 to 4 at the granularity of a namespace. To learn more about MTC see Understanding MTC . Note If you are migrating from OpenShift Container Platform 3, see About migrating from OpenShift Container Platform 3 to 4 and Installing the legacy Migration Toolkit for Containers Operator on OpenShift Container Platform 3 . 1.3. Installing MTC Review the following tasks to install the MTC: Install the Migration Toolkit for Containers Operator on target cluster by using Operator Lifecycle Manager (OLM) . Install the legacy Migration Toolkit for Containers Operator on the source cluster manually . Configure object storage to use as a replication repository . 1.4. Upgrading MTC You upgrade the Migration Toolkit for Containers (MTC) on OpenShift Container Platform 4.12 by using OLM. You upgrade MTC on OpenShift Container Platform 3 by reinstalling the legacy Migration Toolkit for Containers Operator. 1.5. Reviewing premigration checklists Before you migrate your application workloads with the Migration Toolkit for Containers (MTC), review the premigration checklists . 1.6. Migrating applications You can migrate your applications by using the MTC web console or the command line . 1.7. Advanced migration options You can automate your migrations and modify MTC custom resources to improve the performance of large-scale migrations by using the following options: Running a state migration Creating migration hooks Editing, excluding, and mapping migrated resources Configuring the migration controller for large migrations 1.8. Troubleshooting migrations You can perform the following troubleshooting tasks: Viewing migration plan resources by using the MTC web console Viewing the migration plan aggregated log file Using the migration log reader Accessing performance metrics Using the must-gather tool Using the Velero CLI to debug Backup and Restore CRs Using MTC custom resources for troubleshooting Checking common issues and concerns 1.9. Rolling back a migration You can roll back a migration by using the MTC web console, by using the CLI, or manually. 1.10. Uninstalling MTC and deleting resources You can uninstall the MTC and delete its resources to clean up the cluster.

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