Upgrading Drupal

Thanks for reading my post. 

I would like to release my Linux server VM running a custom app on the AWS and Azure Marketplace so businesses can easily integrate it into their network.  How would you go about creating an environment that would allow upgrades to the app in the most simplified manner?

Appreciate any thoughts or docs and book recommendations. 

Having just installed a "fresh" test D9.0.2 system using the suggested composer-based template, I am now in the middle of defining users (only got 4), content types, responsive image styles, etc. 

I now would like to have a look at "automagically" migrating my D8.9.2-content nodes to D9.0.2. My site isn't big, but it is in 3 languages (German, English and Italian), maybe some 150 pages. Is there any "proved" tool to migrate those nodes? Thanks for any hints.

Regards 
H. Stoellinger

Hello,

I am in the middle of upgrading my test 8.9.2-site to 9.0.2 using the "drupal/recommended-project" template. I have the entity_usage module (2.0@beta) installed. Every time I now do a drush updb, drush comes back with 

Hello,

I want to upgrade to Drupal 9.

I'm using Mailchimp module in Drupal 8.

In the module page doesn't say anything about Drupal 9 compatibility.

https://www.drupal.org/project/mailchimp

But the upgrade status module says that mailchimp module is up to date then ready for Drupal 9. Now I'm confused.

Is Mailchimp module ready for Drupal 9?

Thank you.

Regards.