Migration from OpenShift Container Platform 3 to 4 overview

OKD 4 clusters are different from OKD 3 clusters. OKD 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 OKD 3 to 4 see About migrating from OpenShift Container Platform 3 to 4.

Differences between OKD 3 and 4

Before migrating from OKD 3 to 4, you can check differences between OKD 3 and 4. Review the following information:

• Architecture

• Installation and update

• Storage, network, logging, security, and monitoring considerations

Planning network considerations

Before migrating from OKD 3 to 4, review the differences between OKD 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 OKD 3 to 4 at the granularity of a namespace. To learn more about MTC see Understanding MTC.

Installing MTC

Review the following tasks to install the MTC:

1. Install the Migration Toolkit for Containers Operator on target cluster by using Operator Lifecycle Manager (OLM).

2. Install the legacy Migration Toolkit for Containers Operator on the source cluster manually.

3. Configure object storage to use as a replication repository.

Upgrading MTC

You upgrade the Migration Toolkit for Containers (MTC) on OKD 4.12 by using OLM. You upgrade MTC on OKD 3 by reinstalling the legacy Migration Toolkit for Containers Operator.

Reviewing premigration checklists

Before you migrate your application workloads with the Migration Toolkit for Containers (MTC), review the premigration checklists.

Migrating applications

You can migrate your applications by using the MTC web console or the command line.

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

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

Rolling back a migration

You can roll back a migration by using the MTC web console, by using the CLI, or manually.

Uninstalling MTC and deleting resources

You can uninstall the MTC and delete its resources to clean up the cluster.