example: sessions: scale out using redis

Former-commit-id: a811648e0bdf83c289656426f8ba67d785b7d5cc

_examples/sessions/database/redis/main.go

@@ -1,6 +1,9 @@
 package main
 
 import (
+	"fmt"
+	"os"
+	"strings"
 	"time"
 
 	"github.com/kataras/iris/v12"
@@ -18,7 +21,7 @@ func main() {
 	// you can replace them based on your running redis' server settings:
 	db := redis.New(redis.Config{
 		Network:   "tcp",
-		Addr:      "127.0.0.1:6379",
+		Addr:      getenv("REDIS_ADDR", "127.0.0.1:6379"),
 		Timeout:   time.Duration(30) * time.Second,
 		MaxActive: 10,
 		Password:  "",
@@ -55,5 +58,20 @@ func main() {
 	sess.UseDatabase(db)
 
 	app := example.NewApp(sess)
-	app.Listen(":8080")
+
+	// TIP scaling-out Iris sessions using redis:
+	// $ docker-compose up
+	// http://localhost:8080/set/$key/$value
+	// The value will be available on all Iris servers as well.
+	// E.g. http://localhost:9090/get/$key and vice versa.
+	addr := fmt.Sprintf(":%s", getenv("PORT", "8080"))
+	app.Listen(addr)
+}
+
+func getenv(key string, def string) string {
+	if v := os.Getenv(strings.ToUpper(key)); v != "" {
+		return v
+	}
+
+	return def
 }