Monitoring, DNS, SSL & HTTP guides

Network and security work pairs badly with vague advice. These guides come from running real production traffic across DNS, certificates, HTTP, and email auth. We cover the gotchas that show up under pressure — the kind of thing you Google at 2am when something stops resolving.

Each topic is short on theory and heavy on what to actually do: the commands, the response codes, the propagation timelines, the failure modes. Where there's a quirk in the spec, we point at it instead of glossing over. Where vendors disagree, we say which one to follow.

Every guide is paired with a PingThat tool that runs the check live in your browser — DNS lookup, SSL inspection, header dump, JWT decode, subnet math. Read the guide, jump to the tool, verify against your own infrastructure. No upload, no signup, no tracking pixels.

Categories below are organized roughly by stack layer: networking first (IP, DNS, TCP), then transport (TLS, HTTPS), then application (HTTP semantics, redirects, JWT), then operations (uptime SLAs, monitoring math, email deliverability). Pick what bites you today.