Use standard log packages to handle simple scenarios, suitable for small tools or CLI applications; 2. Recommend structured log libraries such as logrus, zap or Go 1.21 slog in the production environment, which support log levels, structured fields and JSON output; 3. Add context to the logs such as request ID, user ID and other information, which can be implemented through middleware; 4. Pay attention to log rotation and management, set appropriate log levels and combine tools to implement file segmentation. The article points out that the Go standard library's log package is suitable for simple needs, but the production environment should use a third-party library that supports structured logs, and emphasizes the importance of adding contextual information to the logs, and recommends that log output be managed reasonably to improve maintainability.
Logging is a critical part of any Go application, especially when debugging issues or monitoring behavior in production. The standard library provides a basic logging package, but for more control and flexibility, you'll often want to go beyond it. Here's how to implement logging effectively in a Go app.
Use the Standard Log Package for Simple Cases
Go's built-in log package is a good starting point if you need basic logging. It's simple and works out of the box.
package main
import (
"log"
)
func main() {
log.Println("Application started")
log.Printf("User %s logged in\n", "john_doe")
} This will print log messages to standard error with a timestamp by default. You can customize the output format using log.SetFlags() and change the output destination with log.SetOutput() .
Use this when:
- You're building a small utility or CLI tool
- You don't need advanced features like log levels
- You want zero dependencies
If you need more features like severity levels, structured logging, or JSON output, you'll need to look elsewhere.
Choose a Structured Logging Library for Production Apps
For real-world applications, especially web services or distributed systems, you'll want structured logging. Libraries like logrus , zap , or slog (Go 1.21 ) are great choices.
These libraries let you:
- Set log levels (debug, info, warning, error)
- Add structured fields to logs (like user IDs or request IDs)
- Output logs in JSON or other machine-readable formats
- Customize formatting and output destinations
Here's an example using logrus :
package main
import (
log "github.com/sirupsen/logrus"
)
func main() {
log.SetLevel(log.DebugLevel)
log.WithFields(log.Fields{
"user": "john_doe",
"role": "admin",
}).Info("User logged in")
log.Debug("This is a debug message")
}This outputs something like:
time="2025-04-05T12:00:00Z" level=info msg="User logged in" user=john_doe role=admin
These logs are easier to parse and analyze in tools like Grafana Loki, Elasticsearch, or Datadog.
Add Context to Logs for Better Debugging
One of the most useful practices in logging is attaching context to each log message. This helps you understand what was happening in the system when an event occurred.
For example, in a web app, you might want to log:
- Request ID
- User ID
- HTTP method and path
- Response status
If you're using a router like chi , you can do this with middleware:
func loggingMiddleware(next http.Handler) http.Handler {
return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
log.WithFields(log.Fields{
"method": r.Method,
"path": r.URL.Path,
}).Info("Request received")
next.ServeHTTP(w, r)
})
}This way, every request gets logged with relevant metadata, making it much easier to trace issues.
Another tip: use a context-aware logger. Some libraries like logrus and zap support attaching fields to a context, so you can carry request-specific data through your app layers.
Don't Forget to Rotate and Manage Logs
Even the best logs aren't helpful if they fill up your disk or become unmanageable. Make sure you:
- Use log rotation (daily or by file size)
- Set appropriate log levels in production (usually
infoorwarn) - Consider writing logs to separate files by severity if needed
You can use external tools like logrotate on Linux or configure your logging library to write to a file directly. For example, with logrus , you can set the output to a file:
f, err := os.OpenFile("app.log", os.O_WRONLY|os.O_CREATE|os.O_APPEND, 0644)
if err != nil {
log.Fatal(err)
}
defer f.Close()
log.SetOutput(f)This is especially useful if you're not using a centralized logging system yet.
That's the core of logging in Go — from basics to structured logging and context. It's not complicated, but getting it right early makes a big difference in maintenance.
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