How would you go about writing a very basic implementation of CI/CD platform

I recently learnt rust, finished the rustlings project and now i want to do something which hopefully won't be impossible but challenging in order to understand the language and just how to write better software. So i decided that i could implement a basic CI/CD platform.

So i want to know how other software developers would approach this problem. E.g: What are the most important features you would implement, some possible gotchas, etc.

Thanks.