React server side rendering

Now server-side rendering is quite a must have things for web apps for many reasons, such as fast page appearance leading to good SEO ranking is one of them. I have a react application using react 15.x, obviously, this application has static routes(using react router 3.x). I want to move my home page to server-side rendering. I read lots of blogs, but nobody tells how to move an existing non-ssr app to a partial SSR app.

So the problems I am facing are these:

  1. Everywhere a new node server is created for server-side rendering. That's ok, but how I will import my client's code component there. I don't want to manually pick and move everything(homepage specific code) to node server that will be a lot of work.

  2. if i will be running a separate node server, that will be running on some port(different port from my client application(separate domain and port number)). how my routes will understand to get the markup from SSR server instead of react code server.

  3. I don't want to go for any frameworks(which are dependent on react) like next.js. It's very difficult to move or upgrade the core libraries(react, react-dom). (Next is just for the background not asking the question for react upgrade)I am in process of upgrading react 15.x to react 16.x. we are having many react dependent helper libraries for autosuggest, carousel, slider etc. Those are creating a lot of problem as either the APIs have changed or support has been stopped.Learnt not to add core libraries dependent

  4. Everywhere its mentioned that in SSR you call the server, you get the HTML pertaining to the components, just hydrate it and you will have a better performance. That actually seems magical.But nowhere it is told that how to do that.

Note: I may be ignorant of the depth of this topic, but I expect valuable inputs from the community.