Handle errs returned with etcd properly for config init and migration (#7134)

Returning unexpected errors can cause problems for config handling,
which is what led gateway deployments with etcd to misbehave and
had stopped working properly

cmd/gateway-main.go

@@ -155,9 +155,12 @@ func StartGateway(ctx *cli.Context, gw Gateway) {
 		registerSTSRouter(router)
 	}
 
+	enableConfigOps := globalEtcdClient != nil && gatewayName == "nas"
+	enableIAMOps := globalEtcdClient != nil
+
 	// Enable IAM admin APIs if etcd is enabled, if not just enable basic
 	// operations such as profiling, server info etc.
-	registerAdminRouter(router, globalEtcdClient != nil)
+	registerAdminRouter(router, enableConfigOps, enableIAMOps)
 
 	// Add healthcheck router
 	registerHealthCheckRouter(router)
@@ -215,7 +218,7 @@ func StartGateway(ctx *cli.Context, gw Gateway) {
 		logger.FatalIf(err, "Unable to initialize gateway backend")
 	}
 
-	if globalEtcdClient != nil && gatewayName == "nas" {
+	if enableConfigOps {
 		// Create a new config system.
 		globalConfigSys = NewConfigSys()
 
@@ -242,7 +245,7 @@ func StartGateway(ctx *cli.Context, gw Gateway) {
 
 	// Create new IAM system.
 	globalIAMSys = NewIAMSys()
-	if globalEtcdClient != nil {
+	if enableIAMOps {
 		// Initialize IAM sys.
 		_ = globalIAMSys.Init(newObject)
 	}