Environment Variables

Environment variables are a crucial aspect of managing configuration in Go applications, especially in cloud-based deployments. This guide demonstrates how to read and set environment variables in Go.

Reading Environment Variables

Use os.Getenv() to retrieve the value of an environment variable. It returns an empty string if the variable does not exist.

package main

import (
	"fmt"
	"os"
)

func main() {	
	host := os.Getenv("HOSTNAME")
	if host == "" {
		fmt.Println("HOSTNAME is not set")
		return
	}
	fmt.Println("Hostname:", host)
}

Setting Environment Variables

You can set environment variables for the current process using os.Setenv():

package main

import (
	"fmt"
	"os"
)

func main() {
	err := os.Setenv("RUNTIME_ENV", "production")
	if err != nil {
		fmt.Println("Error setting environment variable:", err)
		return
	}

	appEnv := os.Getenv("RUNTIME_ENV")
	fmt.Println("Runtime Environment:", appEnv)
}

Using os.LookupEnv() for Safe Retrieval

To safely determine if an environment variable is set and retrieve its value, use os.LookupEnv():

package main

import (
	"fmt"
	"os"
)

func main() {
	if dbPort, exists := os.LookupEnv("DB_PORT"); exists {
		fmt.Println("Database Port:", dbPort)
	} else {
		fmt.Println("DB_PORT is not set")
	}
}

Best Practices

• Use os.LookupEnv() instead of os.Getenv() when you need to differentiate between an unset variable and an empty string.
• Centralize configuration management in your Go application, using environment variables to inject configuration at runtime.
• Use a consistent naming convention for environment variables and include an appropriate prefix, e.g., APP_, to avoid clashes.
• Consider using a package like github.com/kelseyhightower/envconfig for more structured environment variable management.

Common Pitfalls

• Forgetting to check if an environment variable is unset when using os.Getenv().
• Hardcoding environment variable values in the source code, which may lead to issues when deploying to different environments.
• Using sensitive information in environment variables without securing access to them.

Performance Tips

• Minimize the repeated access to environment variables by setting them once during the application startup and caching their values if used frequently.
• Avoid setting environment variables within performance-critical loops, as it incurs a syscall overhead.
• When running in containers, be mindful of the Docker and Kubernetes environment variable constraints, and consider optimizing their usage accordingly.