Caching/make the homepage static if possible. I had a project some years ago that had an elastic search backend, adding redis for caching allowed it to run without problems with up to 1000 concurrent users (position 1-10 on HN if I remember right). As someone below pointed out, the majority would want to have a look, not create accounts.
I use zola a static site generator and deploy the pages (for free) to cloudflare pages.
So there's no impact on my servers.
For a product you will get a lot of people from HN reading the landing page but relatively few registrations.
Autoscaling, available on most popular clouds/hosts
For the frontend: put a CDN in front of it, add caching.
In my experience, most folks just want to see what the fuss is about, not so much make an account and start using the app. So as long as your post-login experience can take a few users simultaneously, you should be fine.