D. Intranet/Internet switchover

Answer DescriptionExplanation: A read-only RDS instance is a replica of the primary RDS instance that can handle read requests and increase the read capability of the database system. A read-only RDS instance inherits the network type (intranet or internet) of the primary RDS instance and cannot switch between them. Therefore, option D is the correct answer. References: Create a read-only ApsaraDB RDS for MySQL instance, Instance types for read-only ApsaraDB RDS instances

A. One of SLB's features is the Health Check. If some of the backend ECS instances are down, whereas other backend ECS instances can still provide services, then the system can continue to work normally.
B. When recreating an SLB instance that has an Internet IP address, a new Internet IP address will be assigned to the SLB instance.

C. The DNS service provider used by the domain name (such as abc.com) must support intelligent resolution.

Answer DescriptionExplanation: The DNS service provider used by the domain name (such as abc.com) does not need to support intelligent resolution, because the CNAME address allocated to the domain name will point to an IP address that is intelligently managed by Alibaba Cloud CDN system. Therefore, option C is not a correct description of modifying domain name resolution. References: What is Alibaba Cloud CDN? - CDN - Alibaba Cloud Documentation Center and Alibaba Cloud CDN

B. Service on demand Cloud storage has a huge resources pool, users can apply for and use the resources on demand.
C. High reliability and availability: Provides very high reliability and availability through technologies like 3 redundant copies, automatic failure recovery, etc.
D. Ultra-large scale: Data storage can reach TB or even PB level

Answer DescriptionExplanation: A. Management and maintenance: To prevent emergent service termination, users need to know the underlying detail like how the data is archived in the resource pool. This is incorrect because cloud storage is designed to abstract the underlying details of how the data is stored and managed from the users. Users do not need to worry about the hardware, software, or network issues that may affect the data availability or reliability. The cloud storage provider is responsible for maintaining and managing the storage infrastructure and ensuring the service continuity1.
B. Service on demand Cloud storage has a huge resources pool, users can apply for and use the resources on demand. This is correct because cloud storage is based on the cloud computing model of service on demand, which means that users can request and access the storage resources as needed, without having to purchase or provision them in advance. Cloud storage providers offer flexible pricing models that allow users to pay only for the storage they use2.
C. High reliability and availability: Provides very high reliability and availability through technologies like 3 redundant copies, automatic failure recovery, etc. This is correct because cloud storage uses various technologies and methods to ensure that the data stored in the cloud is always accessible and durable. For example, cloud storage providers typically replicate the data across multiple servers, regions, or zones to prevent data loss due to hardware failure, natural disaster, or human error. Cloud storage providers also use automatic failure recovery mechanisms to detect and repair any issues that may affect the data integrity or availability3.
D. Ultra-large scale: Data storage can reach TB or even PB level. This is correct because cloud storage can handle massive amounts of data, ranging from terabytes (TB) to petabytes (PB) or even exabytes (EB). Cloud storage providers have the infrastructure and expertise to scale up the storage capacity and performance to meet the growing data needs of users. Cloud storage can support various types of data, such as structured, unstructured, or semi-structured data, and various use cases, such as data backup, data archiving, data analytics, or data sharing.
E. Transparent service: Provides the service through a single SDK. This is incorrect because cloud storage is not a transparent service, but a service that requires users to interact with it through a specific interface or protocol. Cloud storage providers usually offer different types of storage services, such as object storage, block storage, or file storage, each with its own characteristics and features. Users need to choose the appropriate storage service for their data and use the corresponding software development kit (SDK), application programming interface (API), or command-line interface (CLI) to access and manipulate the data.
F. High scalability Storage capacity can be dynamically scaled to meet the needs. This is correct because cloud storage is highly scalable, meaning that users can increase or decrease the storage capacity according to their data needs. Cloud storage providers offer elastic storage services that can automatically adjust the storage resources based on the demand, without requiring users to manually provision or deprovision them. Cloud storage also allows users to scale the storage performance, such as throughput, latency, or bandwidth, to optimize the data access and transfer.

D. Security Center

Answer DescriptionExplanation: Security Center is a centralized security management system that dynamically identifies and analyzes security threats, and generates alerts when threats are detected. Security Center provides multiple features to ensure the security of cloud resources and servers in data centers1. Security Center can help the company to quickly resolve its security problems by providing the following benefits:
Unified security management: Security Center automatically collects various log data from the company’s services on the cloud, and implements control over found security threats. Security Center can also manage assets, attacks, vulnerabilities, and threats in the Security Center console2.
Proactive defense: Security Center supports the proactive detection and termination of mainstream ransomware, mining programs, backdoor programs, worms, malicious programs, DDoS trojans, and trojan programs. Security Center also prevents websites from being maliciously implanted with the acts that involve terrorism, politics, dark chains, trojans, and backdoors. This ensures the normal operation of web page information2.
Automated security operations: Security Center automatically traces the sources and causes of attacks. This helps the company understand the ins and outs of intrusion threats and make quick responses. Security Center also supports custom alerts and third-party data migration to the cloud in a secure manner2.

D. X-Forwarded-For

Answer DescriptionExplanation: The X-Forwarded-For field in HTTP header is used to identify the originating IP address of a client connecting to a web server through an HTTP proxy or a load balancer. When the “Obtain the Visitor’s Real IP Address” function is enabled in Alibaba Cloud SLB, the SLB instance adds the X-Forwarded-For field to the HTTP header of each request and forwards the request to the backend server. The backend server can then obtain the real IP address of the visitor from the X-Forwarded-For field1. The format of the X-Forwarded-For field is as follows:
X-Forwarded-For: client, proxy1, proxy2
where the value is a comma+space separated list of IP addresses, the left-most being the original client, and each successive proxy that passed the request adding the IP address where it received the request from. In this example, the request passed through proxy1, proxy2, and then the SLB instance (proxy3).2 References: Obtain client IP addresses - Server Load Balancer - Alibaba Cloud, XForwarded- For - MDN Web Docs

B. Scheduled mode

Answer DescriptionExplanation: According to the Alibaba Cloud Auto Scaling documentation, scheduled mode allows you to configure the scheduled tasks by adding or removing ECS instances for a fixed time. This mode is suitable for scenarios where the service traffic spikes are predictable and periodic. For example, a new media company can use scheduled mode to add or reduce ECS instances dynamically to address service traffic spikes during some busy hours, such as from 07:30 to 09:00 and from 18:30 to 20:00. This mode can help simplify deployment tasks and save costs by avoiding unnecessary scaling activities. References: How Auto Scaling works - Auto Scaling - Alibaba Cloud Documentation Center.

D. PPPoE

Answer DescriptionExplanation: PPPoE stands for Point-to-Point Protocol over Ethernet, which is a network protocol that encapsulates PPP frames in Ethernet frames and allows multiple computers to share a single Internet connection. PPPoE is typically used by Internet service providers (ISPs) to provide broadband access to their customers, such as DSL or cable modem. PPPoE is not a protocol that is commonly supported by Open API for cloud computing service providers, because it is not designed for web-based communication and requires a dedicated connection between the client and the server. Open API, on the other hand, is a term that refers to a set of publicly available application programming interfaces (APIs) that allow developers to access the functionality and data of cloud computing service providers. Open API usually follows standard protocols that are widely used on the web, such as HTTP, Restful, and Web Service. HTTP stands for Hypertext Transfer Protocol, which is the foundation of data communication on the web. HTTP defines how messages are formatted and transmitted, and what actions web servers and browsers should take in response to various commands. HTTP is a stateless protocol, which means that each request is independent and does not depend on any previous requests or responses. Restful stands for Representational State Transfer, which is an architectural style for designing web services that are based on the concept of resources. Restful web services use HTTP methods (such as GET, POST, PUT, and DELETE) to perform operations on resources, and use standard formats (such as JSON or XML) to exchange data. Restful web services are stateless, scalable, and cacheable, and aim to provide a uniform interface for interacting with different types of resources. Web Service is a generic term that refers to any software service that is available over the web and uses a standardized format for communication, such as SOAP or REST. Web Service allows different applications to communicate and exchange data across different platforms and languages. Web Service can be described using a specification language, such as WSDL or OpenAPI, which defines the structure, operations, and parameters of the service. Web Service can also be registered and discovered using a directory service, such as UDDI or Swagger.