tls

A staple of every networking round, and the follow-up is always about TLS termination. Knowing which layer sees what decides most of the answer.

The oldest question in systems interviewing and still the best, because it is unbounded: every layer you can describe is another layer you could debug.

One round trip versus two is the headline, but the ops-relevant differences hide in what stays plaintext, how resumption works, and which middlewares the change broke.

Automation can renew a certificate without deploying it correctly. Check the served leaf and chain, the client trust store and the exact verification failure.

One saturated core on a proxy is rarely about raw traffic volume. It is a parallelism failure with three usual suspects, and the per-thread view names the culprit in minutes.

The leaf is valid and the root is trusted, yet verification fails. The gap lives in the middle of the chain, and the exact verify code names it before you open a single config file.