Quick, fresh install update path from really old to latest version

[JakubJB]

Hi! I found general rule to perform incremental updates .1, .7, one by one and so on, but...
I got OPNsense instance being quite important to run uninterruptible, but running 21.1 version. I'd like to update it to the latest and greatest version, but with minimal count of reboots. Anyone knows the safest way to do that?
Is there a tool that can verify a configuration against given OPNsense version or maybe a configuration conversion tool?
Maybe someone tried and succeeded with fresh install ISO update, but skipping some versions?

[EricPerl]

You can export the configuration file (or copy the entire /conf directory using scp) and import that during a fresh installation.
The first part of the installation process is to a live environment (only committed to disk by using the installer credentials) so you can test the outcome first.

[JakubJB]

I know how to perform fresh install, maybe I should rephrase my question.
I'm worried that ie. v. 25.1.4 freshly installed system will not fully understand v21.1 configuration file, will skip parts of it (services configs, IPsec configs and so on) and I'd be forced to deal with hidden problems.
If only the tool existed, that could convert or verify the consistency of configuration after old config import.

[JakubJB]

I did some tests. Although traffic is flowing correctly through the firewall, the problems appear somewhere else. Crash reports are generated, related to some php migration script, users are uneditable, who knows what else

[EricPerl]

The concern was valid (and you seem to have been proven right).
It's not really surprising since you are ~4 years and 4 versions behind.
I doubt that such tool exists. It seems it would be a maintenance nightmare... So many combinations!

The extent of the conversion effort is very much dependent on the complexity of your existing config, how many plugins you use...
You could try to generate a new config for the features you use and compare formats.
It's not like the iterative upgrades are risk free either (beyond the reboot count).

Good luck!