Network & Ops

Retries turn a blip into an avalanche when idempotency and budgets are missing. Three timeout layers, retryable errors, jittered backoff, idempotency keys.

Not all datacenter routes perform the same. Reading the ASNs in a traceroute tells you whether traffic uses CN2, 163, 9929 or CMI.

401 vs 403? 301 vs 308? Status code confusions, four caching headers, and ready-to-use strategies for assets, HTML and APIs.

Five fields or six? What happens when day-of-month and day-of-week are both set? Cron formats and frequent mistakes.

Can an IP locate your doorstep or reveal your name? The real limits of IP lookups, plus common privacy misconceptions.

Why the browser blocks cross-origin requests. Same-origin policy, simple requests vs preflight, and common misconfigurations.

How to change an API without breaking old clients. URL vs header vs media-type versioning, plus deprecation and migration cadence.

What the number after the slash means: subnet masks, private ranges, and how to tell if two IPs are on the same network.

Caches absorb load but also serve stale data. Cache-key design, TTL strategy, and the three failure modes: penetration, stampede, avalanche.

HTTPS is HTTP plus TLS, not a new protocol. What certificate validation checks, common myths, and why internal traffic needs it too.

Edge cases and trade-offs of four rate-limit algorithms, plus distributed counting, 429s and retry backoff.

What HSTS, CSP and X-Content-Type-Options actually protect, plus a launch-day checklist you can copy.

Retransmit or not? Ordering? Jitter tolerance? Compare TCP and UDP across five dimensions, and what you must rebuild on top of UDP.

What A, AAAA, CNAME, MX and TXT each do, the cache chain a lookup walks, how to pick TTLs, plus debug commands and three common traps.

From typing a URL to a rendered page: parsing, DNS, connecting, sending, processing, responding, sub-resources — plus where time goes and how to debug.

Polling wastes requests, long-polling is semi-real-time, WebSocket is a bidirectional long connection. When each fits, plus heartbeat and reconnect.

Requests are routed to the nearest edge node. DNS-based routing, cache hits versus origin fetch, purge and prefetch, and what belongs on a CDN.

A forward proxy represents the client going out; a reverse proxy represents the server facing users. Position, use, and the gateway role.

Head-of-line blocking, multiplexing, header compression. HTTP/2 gains, and why HTTP/3 moves to QUIC over UDP.

Endless retries on a slow downstream only cause an avalanche. The three breaker states, half-open probing, and serving a fallback instead of blocking.

The producer drops a task in the queue and returns; the consumer handles it later. Async, peak buffering, decoupling, plus duplicate and ordering caveats.

GET can be cached, sits in history, has length limits; POST carries a body and is not cached. Semantics, safety, idempotency, and when it matters.

Treat things as resources and HTTP methods as actions. Resources, status codes, pagination, versioning, and the verb-in-path anti-pattern.