Free Practice Questions for Alibaba Cloud ACP-Cloud1 Exam

Pay-As-You-Go is a billing method that allows you to pay for resources after you use them. You are billed based on the actual usage of resources, such as the number of hours that an ECS instance runs or the amount of data that is transferred. Pay-As-You-Go is suitable for scenarios where the demand for resources is unpredictable, flexible, or short-term1. Pay-As-You-Go has the following advantages for the startup video streaming company:

No upfront payment: The company does not need to pay any fees in advance when they purchase ECS instances. They only pay for the resources that they actually use, which can help them save costs and optimize their cash flow1.

Flexible scaling: The company can easily scale up or down their ECS instances based on the actual demand for their service. They can add more ECS instances during peak hours or events, such as Christmas, and release them when the demand drops. They can also change the configurations of their ECS instances at any time, such as upgrading the CPU, memory, or bandwidth1.

No long-term commitment: The company does not need to commit to a long-term contract or subscription when they use Pay-As-You-Go. They can release their ECS instances at any time without incurring any penalties or fees. They can also switch to other billing methods, such as Subscription or Savings Plan, if their business needs change1.

The other billing methods of ECS are not as suitable as Pay-As-You-Go for the company’s scenario, for the following reasons:

Pay-As-You-Go with Reserved Instances: Reserved Instances are a type of discount coupon that can be used to deduct a portion of the fees incurred by Pay-As-You-Go instances that match the attributes of the Reserved Instances, such as region, zone, instance type, and operating system2. Reserved Instances require upfront payment and have a fixed term of one year or three years. They are suitable for scenarios where the demand for resources is stable and predictable, and where the user wants to enjoy lower prices than Pay-As-You-Go2. However, for the company’s scenario, Reserved Instances are not a good option, because they do not need to purchase a large number of ECS instances for a long period of time, and they want to have more flexibility and scalability in their resource management.

Subscription with Reserved Instances: Subscription is a billing method that allows you to pay for resources in advance for a specific period of time, such as one month, one year, or three years. You are billed based on the specifications and duration of the resources that you purchase, regardless of whether you use them or not. Subscription is suitable for scenarios where the demand for resources is stable and long-term, and where the user wants to enjoy lower prices than Pay-As-You-Go3. Subscription with Reserved Instances can further reduce the cost of Subscription instances by applying the Reserved Instances discounts to them2. However, for the company’s scenario, Subscription with Reserved Instances are not a good option, because they do not want to pay for resources in advance or commit to a long-term contract, and they want to have more flexibility and scalability in their resource management.

Pay-As-You-Go with Savings Plan: Savings Plan is a billing method that allows you to commit to a consistent amount of usage (measured in USD/hour) for a one-year or three-year term, and in exchange, receive a lower price for that usage4. Savings Plan can be applied to any Pay-As-You-Go instances that match the attributes of the Savings Plan, such as region, instance family, or operating system4. Savings Plan is suitable for scenarios where the demand for resources is stable and predictable, and where the user wants to enjoy lower prices than Pay-As-You-Go and more flexibility than Subscription4. However, for the company’s scenario, Savings Plan is not a good option, because they do not want to commit to a consistent amount of usage for a long period of time, and they want to have more flexibility and scalability in their resource management.

References: Pay-As-You-Go - Elastic Compute Service - Alibaba Cloud, Reserved Instances - Elastic Compute Service - Alibaba Cloud, Subscription - Elastic Compute Service - Alibaba Cloud, Savings Plan - Elastic Compute Service - Alibaba Cloud

Cloud computing is characterized by large-scale infrastructure, high availability, on-demand service provisioning, and versatility in handling diverse applications and workloads. It supports both multi-tenant and single-tenant configurations, and although containerization is popular, cloud computing is not limited to container-based architectures.

Alibaba Cloud provides two main options for securely connecting a VPC with a traditional IDC: VPN (Virtual Private Network) and a dedicated leased line connection. These methods enable stable and secure communication between the VPC and on-premises environments. HTTP agents and stepping stones (options B and C) are not standard or secure methods for IDC-VPC connectivity.

 A bastion host is a special-purpose computer on a network specifically designed and configured to withstand attacks. The computer generally hosts a single application, for example a proxy server, and all other services are removed or limited to reduce the threat to the computer. It is hardened in this manner primarily due to its location and purpose, which is either on the outside of a firewall or in a demilitarized zone (DMZ) and usually involves access from untrusted networks or computers. In the context of Alibaba Cloud, a bastion host can be used to securely access and manage multiple ECS instances in a VPC through the Internet. By applying an EIP and binding it to the bastion host, the administrator can use SSH or RDP protocols to log on to the bastion host from the Internet, and then use the same protocols to access other ECS instances in the VPC through the private network. This way, the administrator can avoid exposing all the ECS instances to the Internet, which would increase the risk of attacks and incur higher costs. The bastion host can also be configured with security policies and monitoring tools to enhance the protection of the ECS instances in the VPC. References: Bastion Host, Access an ECS Instance by Using a Bastion Host

In Alibaba Cloud RDS, read-only instances are synchronized from the master instance but do not allow actions such as creating or deleting databases, configuring backup policies, or changing account authorizations. However, you can configure the read-only instance’s whitelist to control access.

Intelligent DNS resolution is a feature of Alibaba Cloud DNS that allows users to configure different IP addresses for the same domain name based on the geographic locations or ISPs of the visitors. This way, visitors can access the nearest or optimal server for better performance and availability. Intelligent DNS resolution does not support web page content caching, which is a function of Alibaba Cloud CDN. Alibaba Cloud CDN is a distributed network that delivers content from the origin server to the edge nodes closest to the end users, reducing the network latency and bandwidth consumption. Alibaba Cloud CDN caches the static content of the web pages, such as images, CSS, and JavaScript files, on the edge nodes, so that the users can access them faster and reduce the load on the origin server. A user will receive data from the cache in the first-time access, and then will be updated from the origin site in subsequent requests based on the cache expiration time.

References:

1: Intelligent DNS resolution - Alibaba Cloud DNS - Alibaba Cloud Documentation Center

4: Alibaba Cloud Content Delivery Network (CDN) performs content acceleration with the support of intelligent DNS resolution The following function_________is NOT included in intelligent DNS resolution.

5: Alibaba Cloud DNS:Alibaba Cloud line for intelligent DNS resolution (September 16, 2020) - Alibaba Cloud Documentation Center

In Alibaba Cloud RDS, multiple databases can be created within a single instance, allowing users to manage different databases under one RDS instance efficiently. However, databases within the same instance must have unique names, and resources such as CPU and memory are shared across databases within the same instance, contrary to the options provided in answers B and C.

Once a VPC is created in Alibaba Cloud, its CIDR Block cannot be modified. This design ensures stability and network consistency within the VPC. To change the network range, a new VPC would need to be created with the desired CIDR Block.

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Before data communication is set up, the security groups match the security group rules one by one to query whether to allow access requests. If the protocol type, port range, authorization type, and authorization object of two security group rules are the same, the following rules apply:

If the two rules have the same priority, the rule of the denial policy takes effect first, and the rule of the allowed policy does not take effect. This is because the security group rules follow the principle of minimum permission, which means that the most restrictive rule is applied when there is a conflict.

If the two rules have different priorities, the rule with a smaller priority number takes effect. This is because the security group rules follow the principle of priority, which means that the rule with a higher priority (lower number) is applied when there is a conflict. References: ECS Security Groups - Alibaba Fundamentals - Cloud Academy, Security group rules - Elastic Compute Service - Alibaba Cloud Documentation Center

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, X-Forwarded-For - MDN Web Docs