First Hop
Client Protocols
- Simple Polling: Default unless low latency is required; stateless HTTP, delayed by the polling interval.
- Long Polling: Held HTTP request gives near real-time for infrequent updates, but bursts add callback latency.
- Server-Sent Events (SSE): One-way HTTP stream; efficient for server push when clients rarely write back.
- WebSockets: Full-duplex persistent channel for high-frequency reads and writes; adds stateful infra.
- WebRTC: Peer-to-peer for audio/video or server-load reduction; requires signaling, STUN, and TURN.
Load Balancers
Connection Pitfalls
Second Hop
Trigger Models
Scaling Assignment
Key Numbers
Interview Scenarios
Bidirectional Delivery Scenarios
High-Volume Fan-Out Scenarios
Consistency and Conflict Scenarios
Deep Dive Fixes
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