Here some tips for migrating. 

1. The first question you should ask yourself is how much of your history you want to keep. Our app started in Mx2.4 and is now on Mx9.34 so you can imagine there are a lot of commits. But we do not need all this history. Keeping the last couple of months is good enough.
2. Do the migration in parts because if you change all in one go and something is not working what was it that broke it? So in Mx9 start with upgrading to the latest Java and put that already in your current production setup.
3. Check your marketplace content and update to the latest possible Mx9 versions.
4. Check your widget and update those to the latest possible versions for Mx9.
5. When that is done we can do a test migration to git. Create a new project and copy your current model over to that new project and start the git migration. Since no history is kept the transition to git will be fast and probably painless.
6. Now we can move to Mx10. The LTS version is coming but since this is a test migration do it to the current latest Mx10 because that will be the closest to the upcoming LTS version.
7. Now try to run your model. It will probably already start working, but you might need to update again some marketplace content to the Mx10 version.
8. Start testing your model. Certain widgets will not work anaymore. Note those down so you can already change those widgets to different versions or remove them all together if they are obsolete in your still current Mx9 version.
9. Plan your Mx10 migration. You will now have a good understanding on what you will encounter when doing the real migration of your application and it gives your developers confidence because they already did (and you can even do this process more then once) the test migrations.

Regards,

Ronald

You can follow these approach to migrating a large Mendix application from Mendix 9 to Mendix 10:

1. Review Mendix 10 Release Notes and Changes: 

• Java 17 Support: Mendix 10 drops Java 8 support and mandates Java 17. If your app still relies on Java 8, you’ll need to refactor your custom Java actions.
• Runtime Changes: Mendix 10 brings significant changes to the runtime environment, including updated runtimes for cloud deployments, which could affect how your app performs and scales.
• Model Refactoring: There might be updates to the model, deprecated functions, or features that are no longer supported.
• UI Framework Changes: Mendix 10 might bring updated widgets or UI components, requiring some modifications in the app’s UI.
• Security Enhancements: Updates in security mechanisms or libraries may require adaptation in your app to ensure compatibility.

2. Backup and Version Control

Make sure you have a complete backup of your Mendix 9 project, including all custom modules, configurations.

3. Start with a Test Environment or Branch

4. Convert the Project to Mendix 10

5. Test the Application Locally  before any commit

Once the project has been migrated to Mendix 10, run the application locally within Mendix Studio Pro to check for issues. Focus on the following areas:

• UI Behavior: Ensure that all UI components work as expected, and there are no rendering or layout issues.
• Business Logic: Test all key business processes and workflows in the app. Make sure all microflows, pages, and logic execute correctly.
• Database: Ensure that the database schema is compatible with Mendix 10, and that there are no issues in data retrieval or updates.
• Performance: Monitor application performance, especially if your app has high usage or is resource-intensive.