advanced

Realtime and streaming APIs

Choose between WebSocket, Server-Sent Events, long polling, and WebRTC based on directionality, latency, scale, and infrastructure.

Realtime API interviews test protocol choice: WebSocket, Server-Sent Events, long polling, and WebRTC—by directionality, latency, scale, proxies, and infrastructure cost.

Subtopics: WebSocket APIs, SSE and long polling, and WebRTC basics.

On interviews: pick a channel for live notifications vs collaborative editing vs media, and describe auth, heartbeats, backpressure, and reconnect.

Common pitfalls: WebSocket everywhere through corporate proxies, no session auth on socket upgrade, and missing ordering or replay after disconnect.

Checklist:

Match protocol to one-way vs bidirectional needs.
Authenticate at connection and per message where needed.
Plan heartbeats, idle timeouts, and reconnect IDs.
Respect proxy buffering and horizontal scale constraints.