// Topic
When a site is down, everything is slow, or you need to quickly understand what broke.
Typical tasks
// Materials on this topic
9 articles
2026-10-16
Most HTTPS problems boil down to a few reasons: incomplete certificate chain, expired certificate, incorrect name in the certificate, mismatch of versions or ciphers, or interference by intermediate equipment. The …
2026-10-14
curl is a command-line HTTP client available on Linux, macOS and Windows 10 and newer. For debugging it is more convenient than a browser: it shows the full request and response, allows you to set any header and method, …
2026-09-30
HTTP has three versions in active use: HTTP/1.1, HTTP/2, and HTTP/3. Methods, headers, and status codes are the same across them, so an application usually doesn’t care which version a request arrived with. The …
2026-09-22
Server metrics and logs don’t show everything. If an error occurred in the user’s browser or in a rare code path, the server may not log anything and the user may simply close the page. For such cases there …
2026-09-22
Lab and field data Lighthouse and WebPageTest measure site speed in controlled conditions: one device, one network, one run. This is convenient during development, but real visitors open the site from slow phones, over …
2026-09-22
KVM (Kernel-based Virtual Machine) — a virtualization subsystem built into the Linux kernel since version 2.6.20. It uses CPU hardware virtualization support (Intel VT-x, AMD-V) and turns the Linux kernel into a …
2026-09-22
Metrics show something is wrong with the system: response time has increased, memory is exhausted, the share of successful requests has dropped. To understand why this happened, you need logs — records of events written …
2026-09-22
Monitoring is the continuous collection and analysis of data about the operation of servers, networks, databases, and applications. Its goal is to detect a problem before users do: to see that disk space is running out, …
2026-09-22
FASTPANEL — a free server control panel developed by the hosting provider FASTVPS team. It is installed on a personal VPS or a dedicated server to manage websites, databases, mail, and backups via a web interface without …