Logging in Go Applications: Best Practices in Practice

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Introduction: Why Logging in Go is Not Just fmt.Println

Logging is the eyes and ears of any application running in production. In the world of Go (Golang), the approach to logging has undergone significant evolution: from simple console output via fmt.Println to powerful structured loggers capable of producing JSON-compatible records for centralized log collection systems (ELK, Grafana Loki, Datadog).

In this article, we will break down best practices for logging in Go in practice, not in theory. You will learn how to configure logging levels, use structured logs, avoid "noise," and handle errors correctly. All code examples are ready to use in your projects.

1. The Standard log Library: When It's Enough and When It's Not

Go provides a built-in log package from the standard library. It is simple but has significant limitations.

Basic Example

package main

import (    "log"    "os")

func main() {    // Configuring output to a file    file, _ := os.OpenFile("app.log", os.O_CREATE|os.O_WRONLY|os.O_APPEND, 0666)    defer file.Close()    log.SetOutput(file)

    log.Println("Application started")    log.Printf("User %s authorized", "admin")    log.Fatal("Critical error: failed to connect to DB")}

Pros:

No need to install third-party dependencies.
Simplicity of use for small scripts or CLI utilities.

Cons:

No logging levels (only Print, Fatal, Panic).
Fixed output format (date, time, message).
No structured fields (key-value).
Poorly parsed by log collection systems.

Conclusion: for production services, microservice architecture, or any application requiring monitoring, the standard log is not suitable. Switch to structured logging.

2. Structured Logging with zerolog: The Modern Standard

The zerolog library is one of the most popular and fastest loggers in Go. It supports logging levels, JSON output by default, and minimal memory allocation.

Installation

go get -u github.com/rs/zerolog/log

Configuration and Usage Example

package main

import (    "os"    "time"

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

func main() {    // Configuring time format    zerolog.TimeFieldFormat = time.RFC3339

    // Console output with colors (for development)    log.Logger = log.Output(zerolog.ConsoleWriter{Out: os.Stderr, TimeFormat: time.RFC3339})

    // For production — JSON to stdout    // log.Logger = zerolog.New(os.Stdout).With().Timestamp().Logger()

    log.Info().Msg("Server started on port 8080")    log.Debug().Str("module", "auth").Msg("User login attempt")    log.Error().Err(err).Str("user_id", "12345").Msg("Authorization error")    log.Fatal().Int("attempt", 3).Msg("Maximum number of attempts exceeded")}