PRINTABLE FIELD NOTES
Life of a Request
Use this before an interview or during a focused review.
Life of a Request
A failing request is a sequence of boundaries. Identify the first divergent observation, then test one explanation.
| URL and browser | Check scheme, hostname, port, path, local cache and service worker. A rendering error can happen after successful networking. |
|---|---|
| DNS | Compare authoritative and recursive answers, record type and TTL. NXDOMAIN differs from timeout and SERVFAIL. |
| Routing and transport | Check address family, reachability, connection establishment, retransmission and QUIC/TCP differences. |
| TLS | Separate client-to-edge and edge-to-origin connections. Check SAN, trust chain, expiry and SNI. |
| HTTP and edge | Record method, path, status, request ID, cache status and security decisions. |
| Origin and dependencies | Correlate logs and traces; divide time among application, database and external dependencies. |
| Return and render | Response transfer and JavaScript/rendering time are separate from TTFB. Validate the user journey, not only a health endpoint. |
Sources and context
- Life of a Request — further reading
- RFC 1034: Domain names concepts
- Cloudflare DNS and proxy model
- RFC 8767 — DNS serve-stale and TTL expiry
- curl manual — --resolve and request timing
- RFC 9000: QUIC
- RFC 9293: TCP
- RFC 8446: TLS 1.3
- Cloudflare SSL/TLS concepts
- OpenSSL s_client — hostname and certificate verification
- Monitoring distributed systems
- Workers observability