What is the best way to handle configuration of a service?

Question

I'm looking for the best way to read config files on large and medium projects in Go.

1. Which library is suitable for reading and writing config files?
2. In what format should I save the config files (config.json or .env or config.yaml or ...)?

Answer 1

There are numerous way to handle the configuration in Golang. If you want to handle with config.json, then look at this answer. To handle with environment variables, you can use os package like:

// Set Environment Variable
os.Setenv("FOO", "foo")
// Get Environment Variable
foo := os.Getenv("FOO")
// Unset Environment Variable
os.Unsetenv("FOO")
// Checking Environment Variable
foo, ok := os.LookupEnv("FOO")
if !ok {
  fmt.Println("FOO is not present")
} else {
  fmt.Printf("FOO: %s\n", foo)
}
// Expand String Containing Environment Variable Using $var or ${var}
fooString := os.ExpandEnv("foo${foo}or$foo") // "foofooorfoo"

You can also use godotenv package:

# .env file
FOO=foo

// main.go
package main

import (
  "fmt"
  "log"
  "os"

  "github.com/joho/godotenv"
)

func main() {
  // load .env file
  err := godotenv.Load(".env")
  if err != nil {
    log.Fatalf("Error loading .env file")
  }
  // Get Evironment Variable
  foo := os.Getenv("FOO")

Look at this source for more.