Networking & Protocols

WebSocket: free-recall review

Crux Free-recall prompts across the WebSocket unit. Answer each in your own words first, then reveal the model answer and compare.

Your altitude — climbing toward senior

ZeroJuniorMiddleSenior

You are at senior altitude — in orbit

◷ 14 min

Retrieval beats re-reading. For each prompt, say or write a full answer from memory before you open the model answer — the effort of recall is what makes the unit stick.

Goal

Reconstruct the unit’s spine — the upgrade, framing and masking, transport choice, backpressure, jittered reconnection, and the scaling ceilings — without looking back at the lessons.

Recall before you leave

01
Why does WebSocket upgrade an existing HTTP connection instead of opening a fresh raw TCP socket, and what happens on the wire right after the 101?
02
Why must client-to-server frames be masked while server-to-client frames must not be?
03
Give two cases where SSE is the better default than WebSocket, and one case where only WebSocket will do.
04
Walk through the backpressure failure mode on a broadcast server and the high-water-mark fix.
05
Why does exponential backoff without jitter still cause a thundering herd, and what is the correct reconnection recipe?
06
Name the three independent ceilings on connections per WebSocket server, and how horizontal scale and HTTP/2 extended CONNECT shift them.

Recap

If you could reconstruct each answer from memory, you hold the unit’s spine: the upgrade reuses the existing connection so infrastructure still routes it; masking defends the wire against cache poisoning; transport choice follows the direction of data flow; backpressure is the canonical OOM, capped by a high-water mark; reconnection must be jittered or it becomes a thundering herd; and scale hits RAM, file descriptors, and NIC ceilings that HTTP/2 multiplexing and pub/sub fan-out push outward.

Continue the climb ↑WebSocket: code and config reading