Explanation
OSS (Object Storage Service) is a secure, cost-effective, and highly reliable cloud storage service that allows you to store, back up, and archive any amount of data in the cloud1. OSS is ideal for storing logs, as it provides 99.9999999999% (12 nines) durability and 99.995% availability or service continuity1. OSS also supports lifecycle management, which allows you to automatically delete or transition objects to lower-cost storage classes based on your predefined rules2. OSS offers four tiers of storage: Standard, Infrequent Access, Archive, and Cold Archive. Each tier is cost-optimized for specific storage patterns1. The Archive and Cold Archive tiers are suitable for storing infrequently accessed data, such as logs, for a long time. The Archive tier offers data retrieval time within one minute, while the Cold Archive tier offers expedited data retrieval time within an hour1. Therefore, OSS can help the website extend the log retention period to 24 months and ensure that logs can be quickly downloaded when needed.
CDN (Content Delivery Network) is a distributed network that delivers content to users based on their geographic locations, the origin sites, and the content delivery nodes3. CDN is mainly used for content distribution, such as static web pages, images, videos, and downloads3. CDN is not suitable for storing logs, as it does not provide data durability or lifecycle management.
Container Service is a high-performance and scalable container application management service that enables you to use Docker and Kubernetes to manage the lifecycle of containerized applications4. Container Service is mainly used for deploying and orchestrating microservices, serverless applications, and big data applications4.
Container Service is not suitable for storing logs, as it does not provide data durability or lifecycle management.
ApsaraDB for RDS (Relational Database Service) is a stable and reliable online database service that supports MySQL, SQL Server, PostgreSQL, MariaDB, and PPAS5. ApsaraDB for RDS is mainly used for storing and processing structured data, such as user information, transaction records, and product catalogs5. ApsaraDB for RDS is not suitable for storing logs, as it is more expensive and less scalable than OSS. References: Object Storage Service (OSS) - Alibaba Cloud, Lifecycle management - Object Storage Service - Alibaba Cloud Documentation Center, Content Delivery Network (CDN) - Alibaba Cloud, Container Service - Alibaba Cloud, ApsaraDB for RDS - Alibaba Cloud

Changing an instance's operating system requires creating a custom image or using a public image, and then replacing the system disk of the instance. This process will cause the instance to restart. Therefore, this statement is false. References: ECS User Guide: Replace the system disk (non-public image) and ECS User Guide: Replace the system disk (public image)

To manually install Alibaba Cloud Security Center on the server, you need to have the system administrator privilege. This is because the Security Center agent requires access to the system files and processes, and can perform security operations such as vulnerability scanning, intrusion detection, and threat blocking. A common user privilege or a database access privilege is not sufficient to install the Security Center agent. An FTP service privilege is irrelevant to the installation process.

According to the Alibaba Cloud ECS documentation1, the recommended instance type for Tomcat is ecs.c5.
xlarge, which has 4 vCPUs and 4 GiB of memory. This instance type is suitable for web applications that require high performance and low latency. The recommended instance type for Memcache is ecs.r5.large, which has 2 vCPUs and 16 GiB of memory. This instance type is optimized for memory-intensive applications that require high memory bandwidth and low latency. Therefore, option D is the most recommended configuration for deploying Tomcat and Memcache on two ECS instances. References: Instance type families and Alibaba Cloud Elastic Compute Service Product Introduction