The thing that they all have in common is that they don’t depend on a web server.
Templated markup should be prebuilt at deploy time, usually using a site generator for content sites, or a build tool for web apps.
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Any project that relies on a tight coupling between client and server is not built with the JAMstack. This would include:
Why wait for pages to build on the fly when you can generate them at deploy time? When it comes to minimizing the time to first byte, nothing beats pre-built files served over a CDN.
With server-side processes abstracted into microservice APIs, surface areas for attacks are reduced. You can also leverage the domain expertise of specialist third-party services.
When your deployment amounts to a stack of files that can be served anywhere, scaling is a matter of serving those files in more places. CDNs are perfect for this, and often include scaling in all of their plans.
Loose coupling and separation of controls allow for more targeted development and debugging, and the expanding selection of CMS options for site generators remove the need to maintain a separate stack for content and marketing.