Logging is crucial for detecting bugs early, tracing issues efficiently, and mitigating hacking attempts. To achieve these benefits, it's essential to set up logging correctly.

This article will teach us how to use Golang to generate logs effectively, including setting up loggers, formatting log messages, and managing log levels. By mastering these techniques, you can ensure robust and reliable logging in your applications.

Basics of Logging in GoLang

Logging is the practice of recording or storing information and messages that provide insights into the behavior and execution of a program.

Logging and monitoring are crucial for several reasons, including:

  • Faster Problem Detection: Issues within the system are identified more rapidly.
  • Quicker Issue Resolution: Reduced time to repair problems, leading to less downtime.
  • Greater System Transparency: Clear visibility into system operations and performance.
  • Enhanced User Experience: Improved reliability and satisfaction for customers.
  • Stronger Security Measures: Better detection and response to security threats.

Prerequisites

  • Go Installation: Ensure that Go is installed on your system. You can download and install it from the official Go website.
  • Text Editor or IDE: Choose a text editor or integrated development environment (IDE) for writing Go code. A popular choice is Visual Studio Code, if you do not have it, you can download it here.

Standard Library Logging

In Golang, the standard package provided for logging is the log package. The log package offers a simple and easy-to-use interface for logging messages, errors, and other information.

The log package also provides a default logger that writes to the standard error and includes methods for formatting output.

Creating Simple Log Entries

The log package offers several methods to log messages:

  • log.Print(): logs a message without a new line.
  • log.Println(): logs a message with a new line.
  • log.Printf(): logs a formatted message.
package main

import (
    "log"
)

func main() {
    log.Print("This is a common log message. ")
    log.Println("This is a log message with a new line.")
    log.Printf("This is a formatted log message: %s", "Signoz")
}

Output:

This is a common log message. This is a log message with a new line.
This is a formatted log message: Signoz

Customizing the log Package

Setting Log Flags

You can configure the output of log messages using flags to include date, time, and file information.

package main

import (
    "log"
)

func main() {
    log.SetFlags(log.Ldate | log.Ltime | log.Lshortfile)
    log.Println("This log message includes date, time, and file information.")
}

Output:

2024/06/27 12:34:56 main.go:9: This log message includes date, time, and file information.

Redirecting Log Output

You can set a custom output destination, such as a file.

Logging to Files:

package main

import (
    "log"
    "os"
)

func main() {
    file, err := os.OpenFile("app.log", os.O_CREATE|os.O_WRONLY|os.O_APPEND, 0666)
    if err != nil {
        log.Fatal(err)
    }
    log.SetOutput(file)
    log.Println("This log message will be written to the file.")
}

Output(app.log )

2024/06/27 12:34:56 main.go:12: This log message will be written to the file.

Handling Log Prefixes

The log package does not have built-in support for different logging levels like Info, Warning, and Error. However, you can create custom loggers to simulate different logging levels.

package main

import (
    "log"
    "os"
)

func main() {
    infoLog := log.New(os.Stdout, "INFO: ", log.Ldate|log.Ltime|log.Lshortfile)
    warningLog := log.New(os.Stdout, "WARNING: ", log.Ldate|log.Ltime|log.Lshortfile)
    // When logging error messages it is good practice to use 'os.Stderr' instead of os.Stdout
    errorLog := log.New(os.Stderr, "ERROR: ", log.Ldate|log.Ltime|log.Lshortfile)

    infoLog.Println("This is an info message.")
    warningLog.Println("This is a warning message.")
    errorLog.Println("This is an error message.")
}

Output:

INFO: 2024/06/27 12:34:56 main.go:12: This is an info message.
WARNING: 2024/06/27 12:34:56 main.go:13: This is a warning message.
ERROR: 2024/06/27 12:34:56 main.go:14: This is an error message.

Third-Party Logging Libraries

In addition to the standard log package provided by Go, several popular third-party logging libraries offerres and flexibility.

These libraries cater to various logging requirements, including:

  • Structured logging
  • Customizable logging levels
  • Efficient log rotation
  • Seamless integration with external systems

Let's discuss some popular logging libraries in GoLang:

logrus

logrus is a structured logging library for Go (Golang) that offers extensive features and flexibility. It is widely used for its ability to handle structured log data efficiently and its customizable logging levels.

Installation and Setup

To use logrus in your Go application, you need to install it using go get on your Terminal /PowerShell:

go get github.com/sirupsen/logrus

After installation, import logrus into your Go code (if there is an error run go mod tidy):

import (
    "github.com/sirupsen/logrus"
)

Basic Usage and Features

  • Structured Logging: Using logrus developers can log key-value pairs or structured data along with regular log messages.
package main

import (
    "github.com/sirupsen/logrus"
)

func main() {
    // Create a new logger instance
    logger := logrus.New()

    // Example of structured logging
    logger.WithFields(logrus.Fields{
        "animal": "whale",
        "size":   5,
    }).Info("A school of whales emerge from the ocean")
}

Output:

INFO[0000] A group of whales emerges from the ocean      animal=whale size=5
  • Logging Levels: logrus provides different logging levels (Trace, Debug, Info, Warning, Error, Fatal, Panic), allowing developers to control the verbosity of log messages based on their severity.
package main

import (
    "github.com/sirupsen/logrus"
)

func main() {
    logger := logrus.New()

    // Set log level to debug to ensure debug messages are logged
    logger.SetLevel(logrus.DebugLevel)

    logger.Debug("This is a debug message")
    logger.Info("This is an informational message")
    logger.Warn("This is a warning message")
    logger.Error("This is an error message")
}

Output:

DEBU[0000] This is a debug message
INFO[0000] This is an informational message
WARNING[0000] This is a warning message
ERROR[0000] This is an error message
  • Hooks and Formatters: logrus supports hooks and formatters, enabling developers to customize how logs are processed and formatted. Hooks allow actions to be taken when logging events occur, while formatters control the output format of log messages.
package main

import (
    "os"
    "github.com/sirupsen/logrus"
)

func main() {
    // Create a new logger instance
    logger := logrus.New()

    // Example of setting a custom formatter
    logger.SetFormatter(&logrus.JSONFormatter{})

    // Logging with the modified logger
    logger.Info("This is a JSON formatted log message")
}

Output:

{
  "level": "info",
  "msg": "This is a JSON formatted log message",
  "time": "2024-06-27T12:00:00Z"
}

Zap

Zap is a high-performance, structured logging library for Go. It is designed for speed and efficiency, making it ideal for performance-critical applications.

Installation and Setup

To use Zap in your Go application, you need to install it using go get on your terminal/powershell:

go get go.uber.org/zap

After installation, you can import Zap into your Go code:

import (
    "go.uber.org/zap"
)

Basic Usage and Features

  • High-Performance Logging: Zap is designed for high-performance logging, providing both a "sugar" (simpler) API and a more complex API for high-performance needs.

Using the "Sugar" API:

package main

import (
    "go.uber.org/zap"
)

func main() {
    // Create a Sugared Logger
    logger, _ := zap.NewProduction()
    sugar := logger.Sugar()
    defer logger.Sync() // Flushes buffer, if any

    // Log a simple message
    sugar.Infow("A simple log message")

    // Log a formatted message
    sugar.Infof("A formatted log message: %s", "example")
}

Output

{"level":"info","ts":1592580737.941046,"caller":"main/main.go:11","msg":"A simple log message"}
{"level":"info","ts":1592580737.941084,"caller":"main/main.go:14","msg":"A formatted log message: example"}

Using the More Complex API:

package main

import (
    "go.uber.org/zap"
)

func main() {
    // Create a Logger
    logger, _ := zap.NewProduction()
    defer logger.Sync() // Flushes buffer, if any

    // Log a formatted message with fields
    logger.Info("A formatted log message",
        zap.String("Observability", "Signoz"),
    )
}

Output:

{
  "level": "info",
  "ts": 1592580737.941084,
  "caller": "main/main.go:14",
  "msg": "A formatted log message",
  "Observability": "Signoz"
}
  • Structured Logging: Zap supports structured logging, allowing developers to include key-value pairs in log entries. This helps in organizing and analyzing log data effectively.
package main

import (
    "go.uber.org/zap"
)

func main() {
    // Create a Logger
    logger, _ := zap.NewProduction()
    defer logger.Sync() // Flushes buffer, if any

    // Example of structured logging
    logger.Info("Structured logging example",
        zap.String("url", "https://signoz.io"),
        zap.Int("attempt", 3),
        zap.Duration("backoff", 2),
    )
}

Output:

{
  "level": "info",
  "ts": 1592580737.941084,
  "caller": "main/main.go:11",
  "msg": "Structured logging example",
  "url": "https://signoz.io",
  "attempt": 3,
  "backoff": 2
}
  • Configuring Zap: Zap is highly configurable, allowing you to customize the logging configuration to meet your needs.
package main

import (
    "go.uber.org/zap"
    "go.uber.org/zap/zapcore"
)

func main() {
    // Custom configuration
    config := zap.Config{
        Encoding:    "json", // Output format (json or console)
        Level:       zap.NewAtomicLevelAt(zapcore.InfoLevel), // Log level
        OutputPaths: []string{"stdout", "./logfile.log"}, // Output destinations
        EncoderConfig: zapcore.EncoderConfig{
            TimeKey:        "ts", // Key for the timestamp field
            LevelKey:       "level", // Key for the log level field
            NameKey:        "logger", // Key for the logger name field
            CallerKey:      "caller", // Key for the caller field
            MessageKey:     "msg", // Key for the message field
            StacktraceKey:  "stacktrace", // Key for the stacktrace field
            LineEnding:     zapcore.DefaultLineEnding, // Line ending character
            EncodeLevel:    zapcore.LowercaseLevelEncoder, // Log level format
            EncodeTime:     zapcore.ISO8601TimeEncoder, // Timestamp format
            EncodeDuration: zapcore.StringDurationEncoder, // Duration format
            EncodeCaller:   zapcore.ShortCallerEncoder, // Caller format
        },
    }

    // Build the logger with the custom configuration
    logger, _ := config.Build()
    defer logger.Sync() // Flushes buffer, if any

    // Log a message with the custom logger
    logger.Info("This is a log message with custom configuration")
}

Output:

{"level":"info","ts":"2024-06-27T12:00:00Z","caller":"main/main.go:29","msg":"This is a log message with custom configuration"

Zerolog

Zerolog is a fast and efficient structured logging library for Go, distinguished by its ability to perform pretty logging in addition to its high performance and low memory overhead.

Installation and Setup

To use Zerolog in your Go application, you need to install it using go get:

go get github.com/rs/zerolog/log

After installation, you can import Zerolog into your Go code:

import (
    "github.com/rs/zerolog"
    "github.com/rs/zerolog/log"
    "os"
)

Basic Usage and Features

  • Efficient Structured Logging: Zerolog supports efficient structured logging, allowing developers to log key-value pairs or structured data along with regular log messages. This helps in organizing and analyzing log data more effectively.
package main

import (
    "github.com/rs/zerolog"
    "github.com/rs/zerolog/log"
    "os"
    "time"
)

func main() {
    // Configure global logger to write to the console
    log.Logger = log.Output(zerolog.ConsoleWriter{Out: os.Stderr})

    // Example of structured logging
    log.Info().
        Str("event", "user_signup").
        Str("user", "johndoe").
        Time("timestamp", time.Now()).
        Msg("User signed up")
}

Output:

12:00AM INF User signed up event=user_signup user=johndoe timestamp=2024-06-27T12:00:00Z
  • Configuring Zerolog: Zerolog is highly configurable, allowing you to customize the logging configuration to meet your needs. You can set different log levels and configure the output format.
package main

import (
    "github.com/rs/zerolog"
    "github.com/rs/zerolog/log"
    "os"
)

func main() {
    // Set global log level to debug
    zerolog.SetGlobalLevel(zerolog.DebugLevel)

    // Configure global logger to write to the console in JSON format
    log.Logger = log.Output(os.Stderr).With().Logger()

    // Log messages with different levels
    log.Debug().Msg("This is a debug message")
    log.Info().Msg("This is an informational message")
    log.Warn().Msg("This is a warning message")
    log.Error().Msg("This is an error message")
}

Output:

{"level":"debug","time":"2024-06-27T12:00:00Z","message":"This is a debug message"}
{"level":"info","time":"2024-06-27T12:00:00Z","message":"This is an informational message"}
{"level":"warn","time":"2024-06-27T12:00:00Z","message":"This is a warning message"}
{"level":"error","time":"2024-06-27T12:00:00Z","message":"This is an error message"}
  • Pretty Logging: Zerolog provides an option to write logs in a human-readable, pretty-printed format, which is useful during development and debugging.
package main

import (
    "github.com/rs/zerolog"
    "github.com/rs/zerolog/log"
    "os"
)

func main() {
    // Configure logger for pretty logging
    log.Logger = log.Output(zerolog.ConsoleWriter{Out: os.Stderr})

    // Example of pretty logging
    log.Info().Str("foo", "bar").Msg("Pretty logging example")
}

Output:

8:28PM INF Pretty logging example foo=bar

Glog

glog is a library for Go that implements logging with severity levels. Developed by Google, Glog offers simple usage patterns and is designed to handle log file rotation automatically. It is an excellent choice for applications that require categorized logging.

Installation and Setup

To use Glog in your Go application, you need to install it using go get:

go get github.com/golang/glog

After installation, you can import glog into your Go code:

import (
    "flag"
    "github.com/golang/glog"
)

Basic Usage and Features

  • Log Severity Levels: glog supports different log severity levels: INFO, WARNING, ERROR, and FATAL. Each level can be used to categorize log messages according to their importance and urgency.
package main

import (
    "flag"
    "github.com/golang/glog"
    "time"
)

func main() {
    // Initialize the command line flags.
    flag.Parse()

    // Set the default log level to INFO.
    flag.Lookup("stderrthreshold").Value.Set("INFO")

    // Log messages with different severity levels.
    glog.Info("This is an info message")
    glog.Warning("This is a warning message")
    glog.Error("This is an error message")

    // Flushes all pending log I/O.
    glog.Flush()
}

Output:

I0628 20:51:18.894766   12527 main.go:16] This is an info message
W0628 20:51:18.895714   12527 main.go:17] This is a warning message
E0628 20:51:18.896319   12527 main.go:18] This is an error message
  • Log File Rotation: glog handles log file rotation automatically, creating log files in the current working directory by default. Log files rotate based on size and time.

To demonstrate log file rotation, use the following example and run it with the -log_dir flag to specify the log directory.

package main

import (
    "flag"
    "github.com/golang/glog"
)

func main() {
    // Initialize the command line flags.
    flag.Parse()
        // Set the default log level to INFO
    flag.Lookup("stderrthreshold").Value.Set("INFO")

    // Log messages to demonstrate file rotation.
    for i := 0; i < 5; i++ {
        glog.Infof("Log message number %d", i)
    }
}

Run the program with:

go run main.go -log_dir=./logs

Output:

I0628 20:58:23.456944   13419 main.go:16] Log message number 0
I0628 20:58:23.457619   13419 main.go:16] Log message number 1
I0628 20:58:23.457630   13419 main.go:16] Log message number 2
I0628 20:58:23.457634   13419 main.go:16] Log message number 3
I0628 20:58:23.457638   13419 main.go:16] Log message number 4

Log15

Package log15 provides an easy-to-use logging toolkit inspired by the io and net/http packages. It enforces logging with key/value pairs, using strings for keys and any type for values. The default format is logfmt, with optional JSON support for output.

Installation and Setup

To use Log15 in your Go application, you need to install it using go get:

go get github.com/inconshreveable/log15

After installation, you can import log15 into your Go code:

import (
    "github.com/inconshreveable/log15"
)

Basic Usage and Features

  • Structured Logging with Key-Value Pairs: log15 excels in structured logging using key-value pairs, making log entries more informative and easier to search and analyze.
package main

import (
    "github.com/inconshreveable/log15"
)

func main() {
    // Create a new logger
    logger := log15.New()

    // Log a structured message with key-value pairs
    logger.Info("User signup", "username", "akhigbeeromo", "email", "akhigbeeromo@signoz.com")
}

Output:

INFO[06-29|02:36:13] User signup                              username=akhigbeeromo email=akhigbeeromo@signoz.com
  • Handlers for Different Outputs: log15 supports handlers, allowing logs to be directed to different outputs such as the console, files, or remote systems.
package main

import (
    "github.com/inconshreveable/log15"
    "os"
)

func main() {
    // Create a new logger
    logger := log15.New()

    // Create a file handler
    file, err := os.Create("app.log")
    if err != nil {
        log15.Crit("Failed to create log file", "err", err)
        return
    }
    fileHandler := log15.StreamHandler(file, log15.LogfmtFormat())

    // Set the logger to use both console and file handlers
    logger.SetHandler(log15.MultiHandler(
        log15.StderrHandler, // Log to stderr
        fileHandler,         // Log to the file
    ))

    // Log a message
    logger.Info("Application started", "version", "1.0.0")
}

Output(Console and app.log file):

INFO[06-27|15:00:00.123] Application started version=1.0.0
  • Configurable Log Levels: log15 allows configuring log levels to filter log messages according to their severity.
package main

import (
    "github.com/inconshreveable/log15"
)

func main() {
    // Create a new logger
    logger := log15.New()

    // Set the log level to INFO
    logger.SetHandler(log15.LvlFilterHandler(log15.LvlInfo, log15.StdoutHandler))

    // Log messages with different levels
    logger.Debug("This is a debug message") // This will not be logged
    logger.Info("This is an info message")
    logger.Warn("This is a warning message")
    logger.Error("This is an error message")
}

Output:

INFO[06-29|02:42:56] This is an info message
WARN[06-29|02:42:56] This is a warning message
EROR[06-29|02:42:56] This is an error message

Seelog

seelog is a versatile and flexible logging library for Go, designed to provide a wide range of features including asynchronous logging, multiple output destinations, and customizable log formats. Its configuration is managed through XML, allowing for detailed and easy-to-manage log settings.

Installation and Setup

To use seelog in your Go application, you need to install it using go get:

go get github.com/cihub/seelog

After installation, you can import seelog into your Go code:

import (
    "github.com/cihub/seelog"
)

Basic Usage and Features

  • XML-based Configuration: seelog uses XML for its configuration, enabling you to define log levels, output formats, and destinations in a structured manner.

Example seelog.xml configuration file:

<seelog minlevel="info">
    <outputs formatid="main">
        <console/>
        <rollingfile type="size" filename="logs/app.log" maxsize="1000000" maxrolls="5"/>
    </outputs>
    <formats>
        <format id="main" format="%Date %Time [%LEVEL] %Msg%n"/>
    </formats>
</seelog>

Loading the XML configuration in your Go application:

package main

import (
    "github.com/cihub/seelog"
)

func main() {
    // Load XML configuration
    logger, err := seelog.LoggerFromConfigAsFile("seelog.xml")
    if err != nil {
        seelog.Critical("Error parsing seelog config file", err)
        return
    }
    seelog.ReplaceLogger(logger)
    defer seelog.Flush()

    // Log messages with different severity levels
    seelog.Info("This is an info message")
    seelog.Warn("This is a warning message")
    seelog.Error("This is an error message")
}

Output:

2024-06-29 02:51:30 [INFO] This is an info message
2024-06-29 02:51:30 [WARN] This is a warning message
2024-06-29 02:51:30 [ERROR] This is an error message
  • Asynchronous Logging: seelog supports asynchronous logging, which can improve performance by not blocking the main execution flow while logging.

Enabling asynchronous logging in the XML configuration:

<seelog minlevel="info" asyncinterval="1000000">
    <outputs formatid="main">
        <buffered size="10000" flushperiod="1000">
            <console/>
            <rollingfile type="size" filename="logs/app.log" maxsize="1000000" maxrolls="5"/>
        </buffered>
    </outputs>
    <formats>
        <format id="main" format="%Date %Time [%LEVEL] %Msg%n"/>
    </formats>
</seelog>
  • Multiple Output Destinations: seelog allows logging to multiple destinations, such as console, files, or even network endpoints.

Example configuration for logging to both console and file:

<seelog minlevel="info">
    <outputs formatid="main">
        <console/>
        <rollingfile type="size" filename="logs/app.log" maxsize="1000000" maxrolls="5"/>
    </outputs>
    <formats>
        <format id="main" format="%Date %Time [%LEVEL] %Msg%n"/>
    </formats>
</seelog>
  • Custom Log Formats: Enables highly customizable log messages, including timestamps, log levels, and additional context such as function names and line numbers.
<seelog minlevel="info">
    <outputs formatid="detailed">
        <console/>
    </outputs>
    <formats>
        <format id="detailed" format="%Date %Time [%LEVEL] [%FuncShort @ %File:%Line] %Msg%n"/>
    </formats>
</seelog>

Loading this configuration in your Go application will produce detailed log messages that include function names and line numbers:

2024-06-29 11:17:40 [INFO] [main @ main.go:19] This is an info message
2024-06-29 11:17:40 [WARN] [main @ main.go:20] This is a warning message
2024-06-29 11:17:40 [ERROR] [main @ main.go:21] This is an error message

Klog

klog is a logging library for Go, designed to integrate seamlessly with Kubernetes. It is optimized for use in Kubernetes environments, making it a popular choice for applications running in Kubernetes clusters.

Installation and Setup

To use klog in your Go application, you need to install it using go get:

go get k8s.io/klog/v2

After installation, you can import klog into your Go code:

import (
    "k8s.io/klog/v2"
)

Basic Usage and Features

  • Log Severity Levels: klog supports various log severity levels to categorize log messages by their importance. The main levels are INFO, WARNING, ERROR, and FATAL.
package main

import (
    "k8s.io/klog/v2"
)

func main() {
    // Initialize Klog
    klog.InitFlags(nil)

    // Log messages with different severity levels
    klog.Info("This is an info message")
    klog.Warning("This is a warning message")
    klog.Error("This is an error message")

    // klog.Fatal logs a message, then calls os.Exit(255)
    // Uncommenting the following line will terminate the program
    // klog.Fatal("This is a fatal message")

    // Flushes all pending log I/O
    klog.Flush()
}

Output:

I0629 11:28:56.915255   41443 main.go:12] This is an info message
W0629 11:28:56.915394   41443 main.go:13] This is a warning message
E0629 11:28:56.915403   41443 main.go:14] This is an error message
  • Integration with Kubernetes: klog is optimized for use in Kubernetes environments, making it easier to log information in a format that aligns with Kubernetes logging standards.
package main

import (
    "k8s.io/klog/v2"
    "flag"
)

func main() {
    // Initialize Klog
    klog.InitFlags(nil)
    flag.Set("v", "2") // Set verbosity level to 2
    flag.Parse()

    // Log messages with different severity levels
    klog.V(2).Info("This is a verbose info message")
    klog.Info("This is an info message")
    klog.Warning("This is a warning message")
    klog.Error("This is an error message")

    // Flushes all pending log I/O
    klog.Flush()
}

Output:

I0629 11:34:01.866797   42049 main.go:15] This is a verbose info message
I0629 11:34:01.866946   42049 main.go:16] This is an info message
W0629 11:34:01.866952   42049 main.go:17] This is a warning message
E0629 11:34:01.866956   42049 main.go:18] This is an error message
  • Support for Structured Logging: klog supports structured logging, allowing you to log key-value pairs for better context and analysis.
package main

import (
    "k8s.io/klog/v2"
)

func main() {
    // Initialize Klog
    klog.InitFlags(nil)

    // Log structured messages with key-value pairs
    klog.InfoS("User signup", "username", "akhigbeeromo", "email", "akhigbeeromo@signoz.io")
    klog.InfoS("Order processed", "orderID", 1234, "amount", 56.78)

    // Flushes all pending log I/O
    klog.Flush()
}

Output:

I0629 11:37:21.144356   42513 main.go:12] "User signup" username="akhigbeeromo" email="akhigbeeromo@signoz.io"
I0629 11:37:21.144577   42513 main.go:13] "Order processed" orderID=1234 amount=56.78

Logxi

Logxi is a minimalistic and high-performance logging library for Go, designed for developers who need fast and efficient logging with minimal overhead.

Installation and Setup

To use Logxi in your Go application, you need to install it using go get:

go get github.com/mgutz/logxi/v1

After installation, you can import Logxi into your Go code:

import (
    "github.com/mgutz/logxi/v1"
)

Basic Usage and Features

  • Minimalistic and Performant: Designed to be fast and simple, with minimal overhead, suitable for high-performance applications.
  • Structured Logging with Key-Value Pairs: Supports logging of key-value pairs, making logs more informative and easier to analyze.
  • Different Log Levels: Provides various log levels (DEBUG, INFO, WARN, ERROR) to control log verbosity.
package main

import (
    "github.com/mgutz/logxi/v1"
)

func main() {
    // Create a logger instance
    logger := log.New("example")

    // Set log level to Debug
    logger.SetLevel(log.LevelDebug)

    // Log messages with different severity levels
    logger.Debug("This is a debug message")
    logger.Info("User signup", "username", "akhigbeeromo", "email", "akhigbeeromo@signoz.io")// an info message
    logger.Warn("This is a warning message")
    // logger.Error("This is an error message")
}

Output:

12:05:40.559250 DBG example This is a debug message
12:05:40.559977 INF example User signup username: akhigbeeromo
   email: akhigbeeromo@signoz.io
12:05:40.560013 WRN example This is a warning message in:

Guidelines for Effective Logging in GoLang

  1. Categorize Logs According to Their Respective Levels

    Log levels categorize messages based on their importance and severity, aiding in effective troubleshooting and monitoring. Log levels include:

    • DEBUG: provides detailed information useful for diagnosing problems.
    • INFO: highlights the progress or status of the application.
    • WARN: Indicates potential issues or situations that may lead to problems in the future.
    • ERROR: logs errors that are recoverable and allow the application to continue running.
    • FATAL: logs critical errors that cause the application to terminate.

  2. Structured Logging: Use structured formats like JSON for logs to enhance searchability and parsing.

  3. Consistent Log Formatting: Maintain uniform log formats across applications for clarity and automated processing.

  4. Log Rotation and Retention: Implement log rotation to efficiently manage log file sizes, prevent disk space overload, and establish retention policies specifying the duration logs are stored before archiving or deletion.

  5. Sensitive Data Handling: Avoid logging sensitive information like passwords or credit card numbers to mitigate security risks and if necessary, ensure it is masked or obfuscated.

  6. Correlation IDs: Utilize unique identifiers (correlation IDs) in logs to trace and link events across different components or services.

  7. Centralized Logging: Aggregate logs from various sources into a centralized logging system (e.g., ELK Stack, Splunk) for easier management and analysis.

  8. Log Enrichment: Enrich logs with additional context such as user details, transaction IDs, or session information to facilitate troubleshooting and analysis.

Monitoring Logs with an Observability Tool

In this article, we have learned about different logging packages and implemented logs using the log package in Golang. However, simply logging events is not enough to ensure the health and performance of your application. Monitoring these logs is essential for gaining real-time insights, promptly detecting issues, and maintaining the overall stability of your system.

Why Monitoring Logs is Important

Here are the key reasons why monitoring logs is crucial:

  1. Issue Detection and Troubleshooting
    • Early Identification: Logs provide comprehensive information about errors and exceptions within the system, enabling early detection and swift resolution.
    • Root Cause Analysis: Detailed log records assist in diagnosing the underlying causes of issues, offering insights into what went wrong and why.
  2. Performance Monitoring
    • Identifying Bottlenecks: Logs can reveal performance issues such as slow response times or resource constraints, allowing for proactive optimization.
    • Resource Utilization Tracking: Monitoring logs help track the usage of resources like CPU, memory, and disk space, facilitating better resource management and capacity planning.
  3. Security and Compliance
    • Security Surveillance: Logs help detect suspicious activities, unauthorized access, and potential security breaches, which is vital for maintaining a strong security posture.
    • Compliance Adherence: Regular log monitoring helps meet regulatory requirements by maintaining and auditing logs as required by various compliance frameworks.
  4. Operational Insights
    • Health Monitoring: Logs provide insights into the health and status of various system components, including hardware, software, and network resources.
    • Operational Metrics: Logs can be used to generate metrics that provide insights into operational efficiency and overall system performance.
  5. Automation and Alerts
    • Automated Notifications: Observability tools can automatically generate alerts based on log data, enabling faster response times and reducing the need for manual monitoring.
    • Anomaly Detection: Advanced log monitoring tools can use machine learning to detect anomalies in log data, helping to identify potential issues before they escalate.

Sending GoLang Logs to Signoz

SigNoz is an open-source observability platform designed to help developers monitor and troubleshoot applications in real-time. It provides a unified interface for capturing and analyzing distributed traces, metrics, and logs, leveraging OpenTelemetry as its primary data collection framework. By utilizing OpenTelemetry, SigNoz ensures compatibility with various application environments and supports a wide range of instrumentation libraries.

Benefits of SigNoz:

  • Comprehensive Observability: Offers end-to-end tracing, metrics, and logging to provide a holistic view of application performance.
  • Real-time Monitoring: Enables real-time tracking of application health, performance, and error rates.
  • Effective Log Management: Centralizes log data for easier management and analysis, helping to identify issues and track application behavior over time.
  • Alerting and Notifications: Supports customizable alerts based on metrics and traces, ensuring prompt response to issues.
  • Open-source Flexibility: Allows for customization and community contributions, promoting continuous improvement.
  • Ease of Integration: Seamlessly integrates with popular frameworks and libraries used in microservices architectures.
  • OpenTelemetry Support: Utilizes OpenTelemetry for data collection, ensuring compatibility and ease of integration with various applications and environments.

Using the Standard log Package to Send Logs to Signoz:

Step 1: Setting up Signoz in your Environment:

SigNoz cloud is the easiest way to run SigNoz. Sign up for a free account and get 30 days of unlimited access to all features.

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You can also install and self-host SigNoz yourself since it is open-source. With 19,000+ GitHub stars, open-source SigNoz is loved by developers. Find the instructions to self-host SigNoz.

Step 2: Building the Application:

Create a new file named main.go and paste the following code block into it:

package main

import (
	"fmt"
	"log"
	"net/http"
	"os"
)

func main() {
	logFile, err := os.OpenFile("application.log", os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0644)
	if err != nil {
		panic(err)
	}
	defer logFile.Close()

	log.SetOutput(logFile)
	log.SetFlags(log.Ldate | log.Ltime | log.Lshortfile)

	http.HandleFunc("/", handleIndex)
	http.HandleFunc("/log", handleLog)
	http.HandleFunc("/data", handleData)
	http.HandleFunc("/error", handleError)

	fmt.Println("Server starting on http://localhost:8080")
	if err := http.ListenAndServe(":8080", nil); err != nil {
		log.Fatalf("Server failed to start: %v", err)
	}
}

func handleIndex(w http.ResponseWriter, r *http.Request) {
	log.Printf("INFO: Accessing index page | method=%s\n", r.Method)
	fmt.Fprintln(w, "Welcome to the Go Application!")
}

func handleLog(w http.ResponseWriter, r *http.Request) {
	switch r.Method {
	case "GET":
		log.Printf("INFO: Handled GET request on /log | method=%s | path=%s\n", r.Method, r.URL.Path)
		fmt.Fprintln(w, "Received a GET request at /log.")
	case "POST":
		log.Printf("INFO: Handled POST request on /log | method=%s | path=%s\n", r.Method, r.URL.Path)
		fmt.Fprintln(w, "Received a POST request at /log.")
	default:
		http.Error(w, "Unsupported HTTP method", http.StatusMethodNotAllowed)
	}
}

func handleData(w http.ResponseWriter, r *http.Request) {
	log.Printf("INFO: Data endpoint hit | method=%s | endpoint=/data\n", r.Method)
	fmt.Fprintln(w, "This is the data endpoint. Method used:", r.Method)
}

func handleError(w http.ResponseWriter, r *http.Request) {
	log.Printf("ERROR: Error endpoint accessed | method=%s | endpoint=/error\n", r.Method)
	http.Error(w, "You have reached the error endpoint", http.StatusInternalServerError)
}

This Go code sets up a basic HTTP server that logs events to a file (application.log) using the standard log package. It demonstrates how to configure logging output and format, define HTTP request handlers, start an HTTP server, and handle errors. Each HTTP handler logs relevant information about incoming requests and responds with appropriate messages or errors to clients. This setup is useful for monitoring and debugging web applications in a structured manner.

After running your application you should see the following output on localhost:8080/:

Output after running the Go Application
Output after running the Go Application

Output after running the Go Application

Step 3: Setting up the Logs Pipeline in Otel Collector

The above code also generates a log file named application.log on the execution of the code. To export logs from the log file generated, an OpenTelemetry Collector needs to be integrated.

You can set up the complete pipeline following this guide. Here is the complete configuration for the above go code:

receivers:
  otlp:
    protocols:
      grpc:
        endpoint: 0.0.0.0:4317
      http:
        endpoint: 0.0.0.0:4318
  hostmetrics:
    collection_interval: 60s
    scrapers:
      cpu: {}
      disk: {}
      load: {}
      filesystem: {}
      memory: {}
      network: {}
      paging: {}
      process:
        mute_process_name_error: true
        mute_process_exe_error: true
        mute_process_io_error: true
      processes: {}
  prometheus:
    config:
      global:
        scrape_interval: 60s
      scrape_configs:
        - job_name: otel-collector-binary
          static_configs:
            - targets:
              # - localhost:8888
  filelog/app:
    include: [<path-to-log-file>] #include the full path to your log file
    start_at: end
processors:
  batch:
    send_batch_size: 1000
    timeout: 10s
  # Ref: <https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/main/processor/resourcedetectionprocessor/README.md>
  resourcedetection:
    detectors: [env, system] # Before system detector, include ec2 for AWS, gcp for GCP and azure for Azure.
    # Using OTEL_RESOURCE_ATTRIBUTES envvar, env detector adds custom labels.
    timeout: 2s
    system:
      hostname_sources: [os] # alternatively, use [dns,os] for setting FQDN as host.name and os as fallback
extensions:
  health_check: {}
  zpages: {}
exporters:
  otlp:
    endpoint: '<https://ingest>.{region}.signoz.cloud:443'
    tls:
      insecure: false
    headers:
      'signoz-access-token': '<SIGNOZ_INGESTION_KEY>'
  logging:
    verbosity: normal
service:
  telemetry:
    metrics:
      address: 0.0.0.0:8888
  extensions: [health_check, zpages]
  pipelines:
    logs:
      receivers: [otlp, filelog/app]
      processors: [batch]
      exporters: [otlp]

Step 4: Viewing Logs in SigNoz

After running the above application and making the correct configurations, you can navigate to the SigNoz logs dashboard to see all the logs sent to SigNoz.

Signoz log output of Go application
Signoz log output of Go application

Signoz log output of Go application

Conclusion

  • Throughout this guide, we've delved into the foundational importance of logging in GoLang application development, emphasizing its role in diagnosing issues, ensuring system stability, and enhancing security.
  • We've explored the benefits of effective logging, including its ability to provide real-time insights into application behavior, facilitate performance monitoring, and support compliance efforts.
  • The guide has provided practical guidelines for effective logging in GoLang, focusing on clarity, context, and actionable insights as key principles for logging implementation.
  • We've examined the standard log package in GoLang, highlighting its basic usage for creating simple log entries and techniques for customizing output formats and log levels.
  • Additionally, we've covered several popular third-party logging libraries like Logrus, Zap, and Zerolog, detailing their installation, setup, and unique features such as structured logging, performance optimizations, and configurable outputs.
  • The integration of SigNoz, an observability tool, with the log package was explored, demonstrating how it consolidates logs, metrics, and traces into a unified dashboard for comprehensive monitoring and proactive maintenance.
  • By following the steps outlined in this guide, developers can effectively set up SigNoz to monitor their GoLang applications, ensuring robust operational visibility and facilitating rapid issue resolution.

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