Monitoring concepts explained

Choose a website monitoring service by how it confirms failures from several locations, how often it checks, how it alerts you and what history it keeps.

API monitoring calls your API on a schedule, checks each response for availability, speed and correct data, and alerts you when a check fails.

SNMP monitoring reads values such as uptime, interface traffic, CPU load and UPS battery state from network devices by OID, on a schedule or via traps.

DKIM signs outgoing mail with a private key; the public key sits in DNS at a selector, so verification survives forwarding.

DMARC is a DNS record that aligns SPF and DKIM results and tells receivers whether to quarantine or reject failing mail.

A DNS cache is a saved copy of a DNS answer kept by your browser, OS, router or resolver, and the TTL sets how long each copy lasts before the next lookup goes out fresh.

A DNS lookup passes through a stub resolver, a recursive resolver and an authoritative server, each playing a different role in finding the answer.

An MX record names a domain's mail servers; its priority number picks which one a sender tries first, lowest number wins.

SPF is a DNS TXT record listing which servers may send mail for a domain, with a 10-lookup limit and a catch-all rule.

A TLS handshake negotiates the version and cipher, verifies the server's certificate and derives a shared key, in one round trip since TLS 1.3.

Mutual TLS adds a client certificate to the handshake, so the server verifies the client too, not just the other way around.

DNS runs on UDP port 53 for ordinary lookups and TCP port 53 for zone transfers and large answers, plus 853 and 443 for the newer encrypted variants.

llms.txt is a proposed file for AI models, not a web standard. Google says it does not use it for Search. Here is what it does and how to check it.

Noindex keeps a page out of search results while still allowing crawling. What the meta tag and X-Robots-Tag header do, when to use them, and how they leak.

A canonical URL names the one real version of a page so duplicates consolidate into it. Self-referencing, cross-domain, and the staging canonical failure.

Synthetic checks run on a schedule from locations you choose; RUM records timings from real visitors. What each catches, what it misses, and when to run both.

A status page shows whether each part of your service works right now, plus the incident record. What to publish, public vs private, and how to write updates.

Without a monitor you hear about an outage from a customer. What takes sites down, what the gap costs, and what to watch beyond a simple up or down check.

Latency, time to first byte and total response time measure nested spans of one request. How each is measured, what is good, and what the gaps tell you.

Uptime is the share of a measured period during which a site answered as expected. What the percentage means, what the nines allow, and how it is measured.

Why a monitoring system reconfirms a failed check from other locations, the three recheck strategies HostTracker supports, and how to choose between them.

Server monitoring checks availability, performance and resource use continuously. What it covers, agent-based versus agentless, and what to alert on.

A DNS blacklist flags IP addresses associated with spam. How a listing happens, often through no fault of yours, and how to check and monitor your status.

The uptime formula in one line, what 99.9% vs 99.99% vs 99.999% costs you in real downtime per year, and how to measure downtime accurately.