Even if you are talking about SSR such as how Next.js does it, you wouldn't be spanning processes from your ruby/php application. You would deploy it as a separ

Even if you are talking about SSR such as how Next.js does it, you wouldn't be spanning processes from your ruby/php application. You would deploy it as a separate application responsible of the frontend, using your ruby/php application as a backend service providing an API. An alternative is to just serve the HTML from your ruby/php and then take over in the frontend, but this is more complex and not worth it in my opinion.