1.4 KiB
Log Guidelines
Logs from zot can be pushed to the popular ELK stack and therefore they
become one of the service level indicators (SLI). It is therefore important to
set guidelines about how we log in this project.
Log Levels
Depending on whether a log message is useful in development or production, set the appropriate level. Development code should use DEBUG level.
Message Format
We use structured logs (currently via the zerolog library).
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Use lower-case strings by default
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The "message" field should not have any formatting strings
For example,
log.Info().Msg(fmt.Sprintf("this is a %s message", "test"))
So that exact string matches are possible on the "message" field.
All parameters should be specified separately as part of the log.
For example,
log.Info().Str("stringParam", "stringValue").Msg("static message")
Separate components
Instead of:
log.Info().Msg("module: message")
use:
log.Info().Str("module", "module").Msg("message")
OR if you want to a reusable logger then:
log.Info().With().Str("module", "module1").Logger().Msg("message")
Errors
Not all errors are really errors.
For example, lookup a cache (fast path) and it throws a not-found error, and we expect to handle it and perform a slow path lookup. Instead of logging the lookup failure at ERROR level, it may be more appropriate to log at DEBUG level and then handle the error.