Updating old Phalcon 1.3 application to work on 3.3 - how much pain am I in for?

Back in 2015 I wrote a relatively large custom application on Phalcon 1.3. I am now going to be creating a very similar new application, to be hosted on an updated server with Phalcon 3.3.

I would like to start by dropping in the old codebase and updating it as needed to get it working on 3.3, then customise it for the new project. But I'm worried the whole framework may have changed since then and the old code is totally out of touch.

Has anyone ever tried to do something like this? Would I be better off starting with a fresh Phalcon app and just stealing ideas from the old one rather than actual code?

First of all - check all blog posts about new phalcon realses, read all of them and check what changes were made, what breaking changes etc.

Most changes might be in validation if you were using model validation a lot.

Thanks for the tips, guys. Most of the upgrade threads are related to upgrading the actual Phalcon lib on the server, which won't be a problem for us - this will be a new server with a fresh install of the newest lib. I'm more concerned about my app's code and which pieces will work and which won't.

My plan is to fire up the latest versions of the Vokuro and INVO sample apps and start making comparisons and changes until my old app works on Phalcon 3.x. Then go from there.