AWS。NET SDK:无法从S3端点访问S3

我的web服务器需要访问S3。当我将它们放置在公共子网中,或将它们放置在私有子网中并使用NAT网关时,一切正常:

IAmazonS3 client = new AmazonS3Client("myaccesskey", "mysecretkey", enRegion);
PutObjectRequest putReq = new PutObjectRequest();
putReq.FilePath = "c:\temp\myphoto.jpg";
putReq.BucketName = "MyBucket";
putReq.Key = "myphoto.jpg";
PutObjectResponse putResp = client.PutObject(putReq);

现在我尝试将web服务器放置在具有S3端点的私有子网中,我的代码无法再访问S3。我需要更改代码吗?