Environment Variables

The following example introduces the utilization of environment variables. First we check if the environment variable is set, is it hasn't then a default will be defined.

main.go

package main

import (
    "encoding/json"
    "log"
    "net/http"
    "os"
    "time"

    "github.com/gorilla/mux"
)

func main() {

    // Check if the environment variables exist and if not set a default
    if len(os.Getenv("GO_APP_HOST")) == 0 {
        os.Setenv("GO_APP_HOST", "0.0.0.0")
    }

    if len(os.Getenv("GO_APP_PORT")) == 0 {
        os.Setenv("GO_APP_PORT", "8080")
    }

    // Set the variables using environment variables
    serverHost := os.Getenv("GO_APP_HOST")
    serverPort := os.Getenv("GO_APP_PORT")

    // Define router
    router := mux.NewRouter()
    router.HandleFunc("/api/health", func(w http.ResponseWriter, r *http.Request) {
        json.NewEncoder(w).Encode(map[string]bool{"ok": true})
    })

    // Configure HTTP server
    srv := &http.Server{
        Handler:      router,
        Addr:         serverHost + ":" + serverPort,
        WriteTimeout: 15 * time.Second,
        ReadTimeout:  15 * time.Second,
    }

    // Run HTTP server
    log.Print("Starting server on " + serverHost + ":" + serverPort)
    log.Fatal(srv.ListenAndServe())
}

With this code, you can now export an environment variable in your shell, for example:

export GO_APP_PORT="8000"

And run the application:

go run .

Now it should start up on port 8000:

2024/06/25 17:06:04 Starting server on 0.0.0.0:8000

Unset it:

unset GO_APP_PORT

The application will fall back to the default port of 8080.

Refactor Project

I like to keep things organized, we can move the logic for defining variables from environment variables.

Create a new file called settings.go and define two functions, moving the logic from main.go, for example:

settings.go

package main

import (
    "os"
)

func getServerHostVar() (serverHost string) {

    if len(os.Getenv("GO_APP_HOST")) == 0 {
        os.Setenv("GO_APP_HOST", "0.0.0.0")
    }

    serverHost = os.Getenv("GO_APP_HOST")

    return
}

func getServerPortVar() (serverPort string) {

    if len(os.Getenv("GO_APP_PORT")) == 0 {
        os.Setenv("GO_APP_PORT", "8080")
    }

    serverPort = os.Getenv("GO_APP_PORT")

    return
}

Then update main.go to utilise these functions for setting serverHost and serverPort:

main.go

package main

import (
    "encoding/json"
    "log"
    "net/http"
    "time"

    "github.com/gorilla/mux"
)

func main() {

    // Set variables from environment variables
    serverHost := getServerHostVar()
    serverPort := getServerPortVar()

    // Define router
    router := mux.NewRouter()
    router.HandleFunc("/api/health", func(w http.ResponseWriter, r *http.Request) {
        json.NewEncoder(w).Encode(map[string]bool{"ok": true})
    })

    // Configure HTTP server
    srv := &http.Server{
        Handler:      router,
        Addr:         serverHost + ":" + serverPort,
        WriteTimeout: 15 * time.Second,
        ReadTimeout:  15 * time.Second,
    }

    // Run HTTP server
    log.Print("Starting server on " + serverHost + ":" + serverPort)
    log.Fatal(srv.ListenAndServe())
}