> Are they basically offering a way to prebuild apps to static assets and host them on CDNs?
Yes. Pretty much. They're a more dev friendly CloudFront. Supports deploying from a git repo out-of-the-box, where there's a separate service for this with CloudFront. More expensive than CloudFront, though.
> How do server-side only things will happen then?
This isn't the main problem they're solving. They expect that you'll have an API somewhere to talk to. But they do have a "functions" feature, which is based on AWS Lambda, so you could use that for things that would otherwise fall under server-side. They also have a simple "forms" feature for basic data collection.
Yes. Pretty much. They're a more dev friendly CloudFront. Supports deploying from a git repo out-of-the-box, where there's a separate service for this with CloudFront. More expensive than CloudFront, though.
> How do server-side only things will happen then?
This isn't the main problem they're solving. They expect that you'll have an API somewhere to talk to. But they do have a "functions" feature, which is based on AWS Lambda, so you could use that for things that would otherwise fall under server-side. They also have a simple "forms" feature for basic data collection.