The HTTP Request Lifecycle: DNS Lookup, TCP Connection, Request, Response
~13 min read
Every HTTP request goes through the same four stages: find the server's address (DNS), open a reliable connection (TCP), send the request, and receive the response — worth understanding since each stage is a place things can be slow or fail.
The HTTP Request Lifecycle: DNS Lookup, TCP Connection, Request, Response is a Pro topic
Sign in, then upgrade to Pro or Power to unlock this topic and the full AI Engineering curriculum.
Key points
- •DNS lookup translates a human-readable name (google.com) into a numeric IP address — the very first stage, since you can't connect without an address
- •TCP connection establishment guarantees reliable, in-order delivery via a handshake; HTTPS adds a further TLS handshake to negotiate encryption
- •The HTTP request stage sends the method, path, headers (including auth), and body — the actual 'what do you want' from the REST fundamentals subtopic
- •The HTTP response stage returns status code, headers, and body, which the client then parses (render HTML, or parse JSON for an API call)
- •Each stage is a real source of latency — DNS delays, fresh TCP/TLS handshakes — which is why connections are often reused across multiple requests instead of reconnecting each time