safe way to upgrade 1.7.0.2 to 1.9.3

[malblack]

Hello,

I have a website running on Magento 1.7.0.2 which I inherited, with lots of extensions installed and custom code (NOT DOCUMENTED or any version control) ARGH!!!!!!
I'm going to move the site to a different hosting company, which houses the other 3 Magento sites we have, but due to the PHP versions It's looking likely I will have to upgrade this site to version 1.9X.

With the site, a spaghetti of a mess of custom code, obsolete code and no clue with some extensions that are installed are actually used or not on the site.

What would be the best approach to upgrade safely?

Is there a tool to detect what extensions installed (manually) are actually used or not within the site.

My initial guess is I will have to download a version of 1.7.0.2 and use some compare tool to see what code has been changed to the default files, from there I'm a bit stuck on how to approach the rest.

any input much appreciated

Mal

[Sinisa · Accepted solution]

There are no easy ways and shortcuts for upgrade, unfortunately. If best practices are not followed, you'll have more work to do.

It's good starting point to compare current version with clean 1.7.0.2 and to see core changes. All core changes should be rewritten on better way which provides you easier upgrade path (using event observers, or classic class rewrite).

The same thing you should to with template files: if they are changed in base/default, you should extract them and move into separate theme (or to merge it with existing custom package/theme).

Then the next step should be upgrading Magento version by copying 1.9.3.2 files over your Magento. Here fun starts. It may happen that upgrade process fails for some reason. Trace errors and exceptions, and try to manually solve the issues.

After you're done with it, then you should check theme files, probably they will miss form_key (you can check how it should look in original files in base/default, and then apply those changes).

And the last step would be checking compatibility with 3rd party extensions. The best thing you could do is to upgrade extension to the newest version (and check if it's not modified), if that's possible.

So, that's what you have to do, in short. If you have any questions, feel free to ask here.