config: Appropriate error message when newer config file is found (#3972)

cmd/config-v17.go

@@ -215,9 +215,10 @@ func validateConfig() error {
 		return err
 	}
 
-	// Check if config version is valid
 	if srvCfg.Version != v17 {
-		return errors.New("bad config version, expected: " + v17)
+		// Older binary but newer config version.
+		// Config version can never be older as it would have migrated.
+		return fmt.Errorf("Expected config version: %s, newer config version found: %s", v17, srvCfg.Version)
 	}
 
 	// Load config file json and check for duplication json keys

cmd/server-main.go

@@ -169,7 +169,7 @@ func initConfig() {
 
 	// Validate config file
 	err = validateConfig()
-	fatalIf(err, "Cannot validate configuration file")
+	fatalIf(err, "Unable to validate configuration file")
 
 	// Once we have migrated all the old config, now load them.
 	err = loadConfig(envs)