What are the techniques for debugging a web application?

Question

PHP

Good day. There is a task to transfer one web application from one server to another. The application was last written back in 2005, and is something big, scary, written in a procedural style in PHP (almost everything is written with @). When moving, the application completely refuses to run on php5.6. It is very difficult to understand the logic of the application. Tell me what are the methods for debugging and understanding what is needed for what?
ps Rewriting the application is not yet an option, it's already a very big functionality. You need to move quickly so that later you can slowly look for a replacement

Answer 1

The correct solution in this case is to raise some kind of vagrant / docker on a new server with an environment as identical as possible to the original one.
In other solutions from the evil one, a full-fledged debug of an application with complex logic is guaranteed man-months.

Answer 2

If you run under Linux, then as an option - to build from the sources the version of php on which the application worked in 2005.

Answer 3

In your case,
- include all logs and warnings
- look at deprecated functions and replace them with previous code
ps It might be easier and cheaper to rewrite the application.

Answer 4

Good afternoon!
Perhaps if the application is complex enough and contains a lot of incomprehensible logical constructs, it will be easier for you to write this application again, if of course you have the resources for this. If you decide to debug the current version, then you need to install xdebug, which will help you deal with all the difficulties :)

Answer 5

PHP7 is very fast and has a lot of nice features.
I would rewrite the application without hesitation.
Just imagine how you will support it. This is hell..

Answer 6

docker is a good solution. I likewise have to maintain a project running on Debian Lenny and PHP 5.2. I am developing on localhost. Lenny with Apache and PHP run in a container. The DBMS is running on the localhost, as usual. Everything is working fine