What is logs?

Logs are records of events that happen inside a computer system, application, or device. Every time something important occurs-like a user logging in, an error happening, or a file being accessed-the system writes a line of text (a “log entry”) to a log file. These entries usually include a timestamp, a description of the event, and sometimes extra details like the user ID or error code.

Let's break it down

  • Timestamp - tells you exactly when the event happened.
  • Log level - indicates the severity (e.g., INFO, WARN, ERROR).
  • Message - a short description of what occurred.
  • Context - optional extra data such as user name, IP address, or stack trace. All of these pieces are combined into a single line that gets appended to a log file or sent to a logging service.

Why does it matter?

Logs help you understand what your system is doing in real time and after the fact. They are essential for:

  • Debugging problems when something goes wrong.
  • Monitoring performance and spotting unusual activity.
  • Auditing for security compliance and investigating incidents.
  • Keeping a historical record for future analysis and improvement.

Where is it used?

  • Web servers (e.g., Apache, Nginx) log requests and errors.
  • Applications write logs to track user actions and internal errors.
  • Operating systems record system events, hardware changes, and security alerts.
  • Cloud services and containers use centralized logging platforms (e.g., ELK stack, Splunk).
  • Network devices like routers and firewalls keep logs of traffic and connections.

Good things about it

  • Provides a clear, chronological view of system activity.
  • Enables quick identification of issues without needing to reproduce them.
  • Supports automated monitoring and alerting when certain log patterns appear.
  • Helps meet regulatory requirements for data retention and security audits.
  • Can be aggregated and analyzed to improve performance and user experience.

Not-so-good things

  • Log files can grow very large, consuming disk space if not managed.
  • Sensitive information may be accidentally recorded, creating security risks.
  • Poorly structured or inconsistent logs make searching and analysis difficult.
  • Over‑logging can generate noise, hiding the important events you actually need.
  • Setting up and maintaining centralized logging infrastructure can be complex and costly.