Convert or use API? Laravel vs Codeignitor

I have a one system in Laravel and one another related system in codeignitor (older one but upgraded to latest codeignitor). They are related but kind of two different applications (independent applications).
I am thinking of having one login for both now and the data of two system may have to exchanged at some point for better management (now they do not interact).
Now I am confused either:

  1. Rewrite or convert codeignitor app totally in laravel
    problem: will cost time and money and codeignitor system is not that small as well.
    Good thing: Laravel is future and having system in two different platforms may not be good for long run, user will have single sign on, Laravel looks future.

2)Keep it in two different platform develop independently and use api for interaction (also i have invested money developing codeignitor system as well so will be waste if I have to change it to laravel).

I am really confused, what should I do? Any thoughts or suggestions?

The obvious thing to do is to ditch both systems and rewrite completely in Symfony. Just kidding. It basically impossible to offer useful advice to these sorts of ill-defined questions.

You say your CI is ‘not that small’. For some people that means replacing might take three days. Or it might take 3 years. Hard to say based on your description.

The part about wasting money already spent is what is known as the sunk cost fallacy. It’s why companies (and governments) will often keep throwing billions of dollars into failed systems because hey, they have ready spent millions on it. Recognizing that spent money is gone is one of the most difficult things to do.

The only real short term requirement that I can see in your question is a single sign on capability. Assuming the systems have similar user requirements then I would think that would be possible without a great deal of effort. But again it depends on the actual implementation.

As far as future data sharing and code maintenance goes, you really need to come up with an actual set of requirements before useful suggestions can be made.

How about this, stop leaning on third party frameworks and just write in good ol’ Php. Now you are really future proof.