New Release ACA-Cloud1 Alibaba Cloud Computing Questions

Session persistence feature in Server Load Balancer means that it can forward the access requests from a single user to the same ECS instance within a certain period to ensure session continuity. This feature is useful for applications that require users to maintain a stateful connection with the backend servers, such as online shopping or banking. Session persistence can be enabled by configuring a cookie timeout period or a source IP hash method in the Server Load Balancer console. References: ACA Cloud Computing Certification - Alibaba Cloud Academy, Server Load Balancer - Alibaba Cloud Academy, Session Persistence - Alibaba Cloud Documentation Center

Auto Scaling is a management service that can automatically adjust elastic computing resources based on your business needs and policies. Auto Scaling supports the following features12:

• Elastic Scale-Out: Automatically adds ECS instances to handle increased workloads.
• Elastic Scale-In: Automatically removes ECS instances to reduce costs when workloads decrease.
• Elastic Self-Health: Automatically replaces unhealthy ECS instances to ensure high availability and reliability.
• Scheduled Scaling: Automatically adds or removes ECS instances based on predefined schedules.
• Predictive Scaling: Automatically predicts future workloads and adjusts ECS instances accordingly.

Elastic Self-Diagnostic is not a feature supported by Alibaba Cloud Auto Scaling. It is a fictitious term that does not exist in the Alibaba Cloud documentation or course materials. References: 1: Auto Scaling: Automatically Adjusts Computing Resources - Alibaba Cloud 2: Auto Scaling:What is Auto Scaling? - Alibaba Cloud

 A, B, C, and D are the correct answers according to the ACA Cloud Computing by Alibaba Cloud Academy Reference Materials and documents. Comprehensive and Detailed Explanation: = A, B, C, and D are the correct answers because ECS is a highly flexible service that can be used independently as a simple web server, or used with other Alibaba Cloud products, such as OSS and CDN, to provide advanced solutions. ECS can be used in applications such as:

• Official corporate websites: ECS can host official corporate websites that require high performance, stability, reliability, and scalability. ECS can also support various web frameworks and languages, such as PHP, Java, Node.js, Python, and Ruby. ECS can also be integrated with other Alibaba Cloud products, such as SLB, CDN, and WAF, to improve the security, availability, and performance of the websites1
• Large-traffic apps: ECS can handle large-traffic apps that require high concurrency, low latency, and high throughput. ECS can also scale up or down based on the real-time traffic demands, and use Auto Scaling to automate the scaling process. ECS can also leverage the Alibaba Cloud network infrastructure, such as VPC, Express Connect, and Global Accelerator, to optimize the network connectivity and performance of the apps2
• Databases: ECS can run various database systems, such as MySQL, PostgreSQL, MongoDB, and Redis, to provide data storage and processing capabilities for different applications. ECS can also use cloud disks or local disks as the storage media for the databases, and choose different disk types, such as SSD, ESSD, and Ultra Disk, based on the performance and cost requirements. ECS can also use RDS or PolarDB to replace the self-managed databases, and enjoy the benefits of managed database services, such as backup, recovery, monitoring, and maintenance3
• Simple web applications: ECS can run simple web applications that do not require complex architectures or high availability. ECS can provide fast memory and the latest CPUs to power the web applications and achieve faster results with low latency. ECS can also use OSS to store static files, such as images, videos, and documents, and reduce the storage cost and load of the ECS instances.

E is an incorrect answer because ECS is not a storage service that provides unlimited online storage. ECS is a compute service that provides virtual machines with limited storage capacity. ECS can use OSS or NAS to expand the storage capacity, but these are separate storage services that have their own pricing and billing methods.

References: 1: Build a Corporate Website 2: Build a Large-Traffic App 3: Build a Database System : [Build a Simple Web Application] : [ECS Overview]

Alibaba Cloud Server Load Balancer (SLB) is a service that distributes network traffic across multiple ECS instances to improve the service capabilities of applications. SLB supports different load balancing algorithms, such as round robin, weighted round robin, and least connections. When using the weighted round robin algorithm, SLB assigns different weights to backend ECS instances based on their processing capabilities. The higher the weight of a backend ECS instance, the more requests it will receive from SLB. However, the weight of a backend ECS instance is not the only factor that determines the load distribution. The number and the weight of other backend ECS instances in the same server group also affect the load balancing result. Therefore, without knowing the weight settings of the remaining 4 ECS instances, we cannot tell what would happen to the load distribution among the 5 ECS instances. The other statements are incorrect because they assume a fixed or proportional load distribution based on the weight of ecs_inst1, which is not necessarily true.

References:

• Alibaba Cloud Server Load Balancer
• [ACA Cloud Computing Certification Exam Preparation Course]
• Alibaba Cloud Computing Exam Question 2022