The maximum number of connections to an RDS instance primarily depends on the memory size of the instance. Higher memory capacity allows for more simultaneous connections, as memory is a key resource in managing and maintaining connections. Alibaba Cloud RDS scales the connection limit based on the instance's memory allocation to ensure stable database performance.

In Alibaba Cloud OSS, a bucket cannot be deleted until all contents, including files and incomplete multipart upload segments, are removed. This prevents accidental data loss by ensuring no objects remain in the bucket before deletion.

To enable Internet access for ECS instances in a VPC, Alibaba Cloud users can use a public SLB with an Internet IP address (Option B) or an SLB with an Elastic IP (EIP) attached (Option C). Both methods allow the SLB instance to receive external requests and forward them to ECS instances within the VPC. Option A is incorrect because it would require a more complex setup without direct Internet access. Option D is incorrect as SLB does not support directly mounting servers from an on-premises data center.

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. 

 According to the Alibaba Cloud VPC documentation1, a virtual private cloud (VPC) is a virtual network dedicated to your Alibaba Cloud account. You have full control over your VPC, such as specifying the CIDR block, configuring route tables and gateways, and creating subnets. A VPC is an isolated network environment that provides security and flexibility for your cloud computing resources. You can use a VPC to build a secure and isolated network environment on Alibaba Cloud, design your network topology, and specify intranet IP addresses or CIDR blocks in this network environment as needed. Therefore, option B is the correct choice for your scenario. References: What is a VPC? and Alibaba Cloud Virtual Private Cloud.

Alibaba Cloud OSS provides monitoring functions such as storage space monitoring, tracking service requests (like PUT and GET requests), and monitoring UV (Unique Visitors) to help analyze usage and performance. However, OSS does not specifically track the device type (e.g., PC or mobile) accessing files, making option B incorrect.

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.

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