Azure AD Connect upgrade best practices and things to avoid

The upgrade was painless when I ran it.  TLS 1.2 was already enabled on the server so the installation just completed without errors.

You could export your AD Connect settings before the upgrade as a backup.  Then if you did run into problems with the upgrade, you could just uninstall AD Connect completely, do a clean installation and import the settings.

The best way to upgrade is to keep the existing server as it is, and install a new server in "staging mode".

- Export the settings from the existing server.
- Install the new ADConnect on a new server indicating that you are using the exported configuration.
- At the end of this installation, stay in "staging mode".
- Verify that all rules are well applied in the same way as on the source.
- Verify that the number of each kind of objects in the Metaverse Search are nearly identical (Nb of users, groups and computers).
- If numbers are correct, switch the old server in staging mode
- Then switch the new server in production mode.

If you have alerts during export (For exemple, Bad order/number of rules) or import, change the configuration on the source, until all is OK.

Thanks Deman,

How can you export configuration from current server and import onto new one?

Depending on the version of ADConnect, that you have, the export configuration (link) could be found in the "View configuration". (Using the ADConnect admin link that should be on the desktop).

If your version is too older, you can download the Powershell from Microsoft:
How to import and export Azure AD Connect configuration settings - Microsoft Entra | Microsoft Docs 
(Curious, I don't see the link anymore on this link).

Another solution to find the script is to find it on a new installation of ADConnect.
=> It can be installed without configure it !

At least, don't remove immediately ADConnect.

It can allow you to rollback if things are very bad with the new server.

Thank you all for the comments, but still have a doubt here.

 Since we are upgrading from Azure AD Connect 1.x to version 2.x, is it valid to add a second server running Azure AD Connect version 2.x  in staging mode while old server is running?

"Since we are upgrading from Azure AD Connect 1.x to version 2.x, is it valid to add a second server running Azure AD Connect version 2.x  in staging mode while old server is running?"

Yes, it's perfectly valid.  It's called a "swing migration" and is a valid way of migrating to a new version of Azure AD Connect.

More information here:
https://docs.microsoft.com/en-us/azure/active-directory/hybrid/how-to-upgrade-previous-version