Not every project is a JSON API. Sometimes you need to render HTML - a landing page, an admin panel, an email template, a server-rendered app. Fiber supports 9 template engines through a single Views interface, so you pick the syntax you like and Fiber handles the rest.

The surprising part is not the number of engines. It is that switching from one engine to another requires changing exactly two lines of code: the import and the engine constructor. Your handlers, layouts, and rendering calls stay the same.

Every Fiber middleware that needs to persist data - sessions, rate limiter counters, cache entries, CSRF tokens - uses the same Storage interface. That means you can swap from in-memory storage to Redis to Postgres to DynamoDB by changing one line of configuration. Your middleware code stays exactly the same.

Most developers discover this the hard way: they build with the default in-memory storage, deploy to production, and realize their rate limiter resets on every restart and their sessions vanish during rolling deployments. The fix is not a rewrite - it is a one-line storage swap.

If you used sessions in Fiber v2, forget everything. Fiber v3 replaced the session system entirely. The store-based API is gone. Sessions are now middleware - you register them once and they are available on every request through the context.

This sounds like a small change. It is not. The new approach changes how you initialize sessions, how you access them in handlers, and how you handle the interaction between sessions and other middleware like CSRF. If you migrate without understanding the new model, you will spend hours debugging session data that silently disappears.