zerolog

Zerolog

The zerolog package provides a fast and simple logger dedicated to JSON output.

Zerolog’s API is designed to provide both a great developer experience and stunning performance. Its unique chaining API allows zerolog to write JSON (or CBOR) log events by avoiding allocations and reflection.

Visit the following resources to learn more:

@opensource@GitHub Repository

Here’s a simple example of using Zerolog in a Go application to log structured data:

Install Zerolog

First, you need to install Zerolog in your Go project:

go get github.com/rs/zerolog/log

Example Code

package main

import (
 "os"
 "time"

 "github.com/rs/zerolog"
 "github.com/rs/zerolog/log"
)

func main() {
 // Configure Zerolog to pretty-print the logs (for development)
 zerolog.TimeFieldFormat = time.RFC3339
 log.Logger = log.Output(zerolog.ConsoleWriter{Out: os.Stderr})

 // Example of a basic log
 log.Info().Msg("Hello, this is an info log!")

 // Example of structured logging with fields
 log.Info().
  Str("event", "user_signup").
  Str("username", "johndoe").
  Int("age", 28).
  Bool("premium_user", true).
  Msg("New user signup")

 // Log an error with more details
 err := someOperation()
 if err != nil {
  log.Error().
   Err(err).
   Str("operation", "database connection").
   Msg("Failed to connect to the database")
 }

 // Log with different log levels
 log.Debug().Msg("This is a debug message")
 log.Warn().Msg("This is a warning message")
 log.Fatal().Msg("This is a fatal error, the program will exit")
}

func someOperation() error {
 // Simulate an error
 return os.ErrInvalid
}

Explanation

Step 1. Configure Zerolog Output:

We configure the logger to output logs in a pretty-print format using zerolog.ConsoleWriter. This is useful for development. In production, you would typically output logs in JSON format (which is the default).

Step 2. Basic Log:

log.Info().Msg("Hello, this is an info log!") logs a simple message at the info level.

Step 3. Structured Logging:

You can attach structured fields to logs using chained methods like Str(), Int(), and Bool(). This makes logs much more informative and easier to query later.
Example:

log.Info().
Str("event", "user_signup").
Str("username", "johndoe").
Int("age", 28).
Bool("premium_user", true).
Msg("New user signup")

Step 4. Error Logging:

In case of errors, Err() can be used to include the error details in the log.
Example: log.Error().Err(err).Str("operation", "database connection").Msg("Failed to connect to the database").

Step 5. Different Log Levels:

Zerolog supports multiple log levels like Info, Debug, Warn, Error, and Fatal.
Fatal logs the message and then exits the program.

Sample Output

With zerolog.ConsoleWriter for pretty-print logs, the output would look like this:

INF Hello, this is an info log!
INF New user signup event=user_signup username=johndoe age=28 premium_user=true
ERR Failed to connect to the database operation=database connection error=invalid argument
DBG This is a debug message
WRN This is a warning message
FAT This is a fatal error, the program will exit

In production (without the pretty-print), Zerolog outputs the logs in JSON format, which is more suitable for log aggregation systems like ELK (Elasticsearch, Logstash, Kibana) or any log management tool.