Migration from older customized ISPConfig instance to latest

I've made some customization to an older ISPConfig 3.1.x release and a few modules that I don't want to maintain any more and want to upgrade to the latest upstream version of ISPConfig on a fresh Debian 12 OS. I have a multi-server setup with some customization, and plan to upgrade them, too. I want to keep the old mail, db and dns servers in the ISPC cluster. They're easy to upgrade or migrate, I can do that manually.

I plan to purchase the migration tool if it's able to do what I need. It's the following:
- copy all customers, web, dns, email account, ftp account and database account config, LE certificates (via certbot)
- copy website data, but nothing else - I want to keep databases, email data and dns records where they are on the "satellite" servers

Is that possible? What is the recommended procedure? The database is not customized, I only made changes to the UI and added a module and DB tables for ProFTPD, which I most likely will just replace with PureFTPD in the new setup.

 

Thanks, as I noted, I'd only migrate the websites data along with the "metadata" of those and everything else. In that case, I'd first create a separate cluster with a single web server first, and then add the old ones to the new cluster. The question is, can I add the existing servers to that cluster later, and existing customers would then refer to those, holding the old data, or do I need to add them before migration so account metadata can refer to them outright? Or in both cases, do I need to configure users so they actually use the satellite servers? I guess the second option would be cleaner. I just need the correct metadata in the databases and I can just migrate the data later. Would that work?

 

I want to standardize on the upstream ISPC releases so I can install upgrades any time without merging code and taking care of a lot of things related to that, so losing customization is not an issue. The ones I do need, are simple enough (some overview panels I developed and an extra database table). They don't need code merging. The rest is either not that important or have been developed in upstream already (most prominently better Dovecot support, bugfixes and some DNS record types or functions, translations, etc).

To simplify things, I could create the new main node (web server), then make a clone of the other ones, remove data from them, then do either a migration process with either the migration toolkit or ispcopy. I'm working in Proxmox with VMs and containers, so it's not a lot of hassle if it works. Why I complicate things is that I use an Exim 4 based email server and a PowerDNS server with a lot of data and those are not or just partly supported by ISPC, but I integrated them via the ISPC database.