What happens when you type a URL in the browser and press Enter?
Answer
- The browser parses the URL; checks HSTS and its cache.
- DNS resolution: browser, OS and resolver caches, then recursive lookup → IP address.
- TCP connection + TLS handshake (or QUIC for HTTP/3).
- HTTP request with headers and cookies; it may pass a CDN, load balancer, reverse proxy, app server, database/cache.
- Response: status, headers (caching, cookies), body.
- Rendering: HTML → DOM, CSS → CSSOM, render tree, layout, paint, composite; scripts may block parsing (unless defer/async); images and other resources are fetched.
- Mention where you would optimize (CDN, caching, compression, fewer round trips).
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