In a SPA, you want to change routes in the URL so you don’t break people’s expectations about being able to share deep links to specific pages, but those sites don’t really exist. Eg if your site is www.example.com and you have a SPA on there, and one of the pages is www.example.com/products, you want to still serve index.html from the root even though the /products path is not a real directory on your system. If you don’t serve for this URL then it’ll work fine locally but if someone hard-refreshes or shares the link, it won’t load.
If you are using Cludfront with an S3 origin you can turn on static website hosting and specify a 404 fallback page[0] - which would then just be your index file. It will render your client code and let you show a 404 if it is indeed one.
The problem is that essentially every time a user goes to the site it will be a 404 status code since they are probably not typing in example.com/index but this has pragmatically not been an issue for a wholly authenticated, private, B2B SaaS app. The marketing website is a separate subdomain.
For a public site this is probably worse than returning 200s that should be 404s occasionally, though.
