Logging is the practice of recording discrete events from a system so you can inspect what happened later.
Logs are usually text records with a timestamp and some context, such as:
- An error message
- A request being handled
- A service starting or stopping
- A dependency timing out
Why people use it
Logging helps answer questions such as:
- What happened right before an error?
- Which code path ran?
- What inputs were received?
- What state did the system have when something failed?
Compare
Logging is one of the three main signals in Observability.
- Metrics tell you how much or how often
- Traceability tells you where a request went
- Logging tells you what happened at a specific point in time
Related idea
Logs are often correlated with Metrics and Traceability using IDs, timestamps, and request metadata.