Add simple method of configuring via envars

config.go

@@ -4,17 +4,29 @@ import (
 	"encoding/json"
 	"fmt"
 	"os"
+
+	"github.com/caarlos0/env"
 )
 
 func ReadConfig(configName string, target interface{}) error {
 	filename := fmt.Sprintf("/etc/sensu/%s.json", configName)
+
+	// First attempt to open the file
 	file, err := os.Open(filename)
-	if err != nil {
+	if err == nil {
+		decoder := json.NewDecoder(file)
+		err = decoder.Decode(target)
+		if err != nil {
+			return err
+		}
+	} else if !os.IsNotExist(err) {
+		// We don't need the error if it was a does not exist because it's still
+		// possible to configure via envars.
 		return err
 	}
 
-	decoder := json.NewDecoder(file)
-	err = decoder.Decode(target)
+	// Override any json value with envars
+	err = env.Parse(target)
 	if err != nil {
 		return err
 	}

go.mod

@@ -1,6 +1,7 @@
 module github.com/sensu-utils/toolbox
 
 require (
+	github.com/caarlos0/env v3.5.0+incompatible
 	github.com/coreos/etcd v3.3.12+incompatible // indirect
 	github.com/dgrijalva/jwt-go v3.2.0+incompatible // indirect
 	github.com/echlebek/timeproxy v1.0.0 // indirect