RDS provides whitelist access policies. You can set permitted IP addresses and IP network segments to effectively prevent hackers from attacking the server by port scanning1. A whitelist is a list of IP addresses or CIDR blocks that are allowed to access an RDS instance. By default, the whitelist is empty, which means that no IP address can access the RDS instance. You can add IP addresses or CIDR blocks to the whitelist to allow access from specific sources. You can also modify or delete the whitelist as needed2. Whitelist access policies help improve the security of your RDS instance and protect your data from unauthorized access3.

Alibaba Cloud RDS uses a master-slave or primary-replica architecture to provide high availability. In the event of a master database failure, automatic failover to the standby instance generally occurs within 30 seconds, helping to minimize downtime and maintain service continuity.

Alibaba Cloud Object Storage Service (OSS) is a cloud storage service that allows you to store, retrieve, and manage data in the cloud. OSS provides multiple file uploading modes for different scenarios, such as simple upload, multipart upload, append upload, resumable upload, and cross-region replication. These uploading modes can be implemented by using the API or the SDK provided by OSS. Therefore, options B and D are the correct answers. Option A is not correct because the OSS management console only supports simple upload for files that are smaller than 5 GB. Option C is not correct because OSS does not support directly copying to/from OSS using portable disks. References: Object Storage Service:Simple upload, Object Storage Service:Multipart upload, Object Storage Service:OSS tools

For Layer-4 SLB using TCP, the health check determines ECS instance availability based on the successful completion of a TCP 3-way handshake. This ensures that the backend server is reachable and can accept connections, which is critical for reliable TCP-based load balancing.