通过编程将DynamoDB GSI设置为自动缩放

我正在使用 registerScalableTarget 将全局二级索引设置为自动缩放。下面是我的代码。我没有收到任何错误消息。

var registerScalableTargetForWCU= function(event, callback) {
   var params= {
       ServiceNamespace: "dynamodb", RoleARN: event.roleArn,
       ResourceId: "table/TableName/index/IndexName",
       ScalableDimension: "dynamodb:index:WriteCapacityUnits",
       MinCapacity: 1, MaxCapacity: 2
   };
   applicationautoscaling.registerScalableTarget(params, function(err, res) {
       err ? callback(err) : callback(null, res);
   });
}

describeScalableTargets

{ ScalableTargets: [ { ServiceNamespace: 'dynamodb',
   ResourceId: 'table/TableName/index/IndexName',
   ScalableDimension: 'dynamodb:index:ReadCapacityUnits',
   MinCapacity: 1,
   MaxCapacity: 1,
   RoleARN: 'RoleARN',
   CreationTime: 2017-08-06T08:32:30.294Z },
 { ServiceNamespace: 'dynamodb',
   ResourceId: 'table/TableName/index/IndexName',
   ScalableDimension: 'dynamodb:index:WriteCapacityUnits',
   MinCapacity: 2,
   MaxCapacity: 10,
   RoleARN: 'RoleARN',
   CreationTime: 2017-08-06T08:32:30.460Z } ] }