Alibaba Cloud ACP-Cloud1 Dumps

 A DDoS attack is a type of cyberattack that aims to exhaust the resources of a target server or network, such as bandwidth, CPU, memory, or disk space, by sending a large amount of malicious traffic or requests. This can cause the server or network to slow down, crash, or become unavailable to legitimate users. A DDoS attack is not intended to steal confidential information, crack passwords, or target databases, although these may be secondary objectives or consequences of some attacks. A DDoS attack is one of the most common and powerful threats to website security, as it can be launched from multiple sources, use various attack methods, and evade traditional defense mechanisms. According to the DDoS Attack Statistics and Trend Report by Alibaba Cloud, the proportion of volumetric attacks at 50Gbps and above has doubled, and the resources exhaustion attack reached a peak value of 3 million QPS in 2020-2021. References: DDoS Attacks: Sources, Strategies and Practices - Alibaba Cloud, DDoS Attack Statistics and Trend Report by Alibaba Cloud, Use Alibaba Cloud Anti-DDoS Service to Defend DoS Attack, Anti-DDoS Basic - Alibaba Cloud

ApsaraDB for RDS is Alibaba Cloud's managed database service that simplifies O&M tasks for relational databases like MySQL. It offers built-in features for automatic backups, high availability, and Master/Slave synchronization, which reduces manual intervention and helps scale the database as traffic grows. By migrating to ApsaraDB for RDS, users can offload complex O&M responsibilities to Alibaba Cloud, ensuring a more efficient and scalable database solution for high-traffic applications.

Different Alibaba Cloud VPCs are completely isolated from each other by default, but they can communicate with each other over the intranet by using different methods, such as Cloud Enterprise Network (CEN), VPN gateways, VPC peering connections, and PrivateLink. These methods allow you to establish secure and reliable connections between VPCs without exposing your network traffic to the internet. References:

Overview of VPC connections - Alibaba Cloud

Cross-VPC peering - Alibaba Cloud

ALIYUN::VPC::VpcPeerConnection - Alibaba Cloud

 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.

During cool-down time, scaling activities in the same scaling group are temporarily locked to avoid unnecessary scaling activities. The cool-down time begins once all ECS instances in a multi-instance scaling action are added or removed.

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Even though the scaling rule is set to "Adjust to 10 ECS instances," the maximum instance limit set for the scaling group is 8. Thus, when the scheduled task is triggered, Auto Scaling will increase the number of instances up to the maximum allowed, which is 8. Therefore, the scaling group will contain 8 instances, not 10, as it adheres to the defined maximum limit.

Alibaba Cloud Object Storage Service (OSS) does not solely rely on RAID 0+1 redundancy technology to achieve high data reliability. OSS uses a distributed system architecture to store data across multiple devices and servers. OSS also supports cross-region replication (CRR) to replicate data across different regions for disaster recovery. OSS is designed for 99.9999999999% (12 9’s) data durability and 99.995% service availability12. References:

Object Storage Service (OSS) - Alibaba Cloud

What is OSS? - Object Storage Service - Alibaba Cloud Documentation Center

Alibaba Cloud OSS automatically maintains three copies of each data object to ensure data reliability and redundancy. This setup allows OSS to recover data automatically without human intervention in case of hardware or system failures, ensuring high data durability.

Alibaba Cloud OSS provides three primary access permissions for buckets: Private, Public-read, and Public-read-write.

Private: Only the owner has access to read or write data.

Public-read: The owner can read and write, but others can only read.

Public-read-write: The bucket is fully open for reading and writing by all users.There is no Private-read permission in OSS access control options, so option A is incorrect.

When the black hole policy is triggered by excessive DDoS traffic, the affected server is temporarily isolated from the network to prevent further damage. During this period, no services are available, meaning the server cannot provide limited-speed services.

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.

Alibaba Cloud OSS (Object Storage Service) is designed for storing large volumes of unstructured data, such as files, images, and videos, making it an optimal solution for network disk applications. By migrating storage from ECS data disks to OSS, the team can offload storage tasks, reduce the number of ECS instances required, and significantly lower O&M costs. OSS also provides high scalability, reliability, and cost-effectiveness for such use cases.

In this scenario, a combination of Server Load Balancer (SLB), ECS, ApsaraDB for RDS, and Auto Scaling is ideal. SLB distributes incoming traffic across multiple ECS instances, ensuring high availability and reliability. Auto Scaling automatically adjusts the number of ECS instances based on demand, managing costs efficiently by scaling out during peak times and scaling in when demand decreases. ApsaraDB for RDS provides a managed database service that handles increasing database demands without requiring complex manual scaling. This portfolio is optimal for fluctuating gaming traffic as it ensures load balancing, scalability, and cost control.

In Alibaba Cloud VPCs, only custom route tables can be created and deleted by users. The default route table associated with each VPC cannot be deleted, although custom routing entries within it can be modified. This limitation ensures the integrity of essential VPC networking components.

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Auto Scaling in Alibaba Cloud is designed to automatically adjust resources, such as ECS instances, based on the demand and scaling policies. This works best with applications that are stateless and horizontally scalable, as these applications do not rely on data stored locally on an instance, allowing them to scale in and out without affecting performance or user experience. Statelessness and horizontal scalability allow Auto Scaling to manage ECS instances efficiently without manual intervention.

When changing the specifications of an RDS instance, service interruptions can occur during some upgrade and downgrade operations, depending on the RDS instance type and the complexity of the change. While upgrades are generally supported, certain modifications may result in brief downtime as the system reconfigures resources. This is contrary to option B. Additionally, database version downgrades are restricted, and MySQL 5.1 can indeed be upgraded directly to MySQL 5.6 in Alibaba Cloud RDS.

Using lifecycle hooks in Auto Scaling allows for custom operations, such as updating the Redis whitelist when instances are added or removed. An OOS (Operation Orchestration Service) template can automate this process, and MNS (Message Notification Service) can trigger events to inform Redis when changes occur.

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Modifying the MAC address of an ECS instance’s NIC can cause network disconnection issues because Alibaba Cloud's VPC network infrastructure relies on consistent NIC configuration. Changing the MAC address may prevent the instance from being identified correctly on the network.

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Alibaba Cloud RDS allows multiple databases to be created on a single instance. However, each database within the same instance must have a unique name, and resources are shared among instances unless specified otherwise. Additionally, not all RDS editions support High Availability (HA) mode; HA is typically available in certain editions, like RDS for MySQL and RDS for PostgreSQL.

In SLB, a Listener is configured with policies and forwarding rules that define how the load balancer will handle incoming requests, including protocol, port, and health check configurations. It does not represent an SLB instance itself or a collection of ECS instances, but it plays a crucial role in managing traffic routing and session persistence.

Alibaba Cloud OSS (Object Storage Service) is the ideal solution for storing large volumes of video data generated by a surveillance system. OSS provides scalable, secure, and cost-effective storage that can accommodate growing data needs without the space limitations of local ECS disks. Additionally, OSS enables easy access to historical data when required, making it well-suited for video storage in use cases like surveillance.

Alibaba Cloud Object Storage Service (OSS) is ideal for storing large amounts of unstructured data, such as images and videos. By migrating static files to OSS, you can free up disk space on your ECS instance, allowing you to efficiently handle storage needs as your business scales. OSS is a highly scalable and cost-effective solution for handling media files and other static assets.

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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.

Alibaba Cloud ECS allows users to set an auto-release time for Pay-As-You-Go instances, giving flexibility in handling temporary workloads without manually releasing instances. Notably, the auto-release time can be adjusted multiple times even after the instance has been created, allowing for modifications as business needs change. This feature provides a convenient way to manage costs by automatically releasing instances when they are no longer needed. However, once the auto-release time is set, it must be adjusted or canceled if changes are required.

OSS provides the fragment management function to help you delete the fragment files left in OSS after you forget to invoke the “Complete Multipart Upload” interface. Fragment management allows you to list, delete, or restore the fragment files in a bucket. You can use the OSS console, OSS SDKs, or OSS APIs to perform fragment management operations. OpenAPI batch deletion, online batch deletion, and bucket clearing are not the functions provided by OSS to delete the fragment files. 

RDS for MySQL supports connections through tools that are compatible with MySQL, such as MySQL-Front, Navicat MySQL, and command-line MySQL commands. SQL Server Management Studio (SSMS) is designed for Microsoft SQL Server and is not compatible with MySQL, so option D is incorrect.

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.

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. References: Security Center - Alibaba Cloud, Cloud Security- Alibaba Cloud, Introduction to Security Center - Alibaba Cloud Document Center

Alibaba Cloud Object Storage Service (OSS) is ideal for storing unstructured data, including media files such as pictures, videos, and documents. OSS offers scalable storage, high durability, and easy access, making it well-suited for handling large volumes of unstructured data.

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According to the Alibaba Cloud Academy, Auto Scaling supports three scaling modes: manual mode, scheduled task, and cloud monitor and event-triggered task. Manual mode requires manual intervention to adjust the number of ECS instances, which is not feasible and with minimum operation efforts. Scheduled task allows you to set the time and number of ECS instances to be added or removed in advance, which is suitable for predictable traffic changes. Cloud monitor and event-triggered task allows you to set the monitoring metrics and thresholds for scaling actions, which is suitable for dynamic traffic changes. Healthy check mode is not a scaling mode, but a feature of SLB to ensure the availability of ECS instances behind the load balancer. References: : ACP Cloud Computing Certification Preparation Course - Auto Scaling, : ACP Cloud Computing Certification Preparation Course - Server Load Balancer

 To execute a task at a specific time such as removing 1 ECS instance every night at 00:00, you need to perform two operations: create a scaling rule and create a scheduled task. A scaling rule is a set of instructions that defines how Auto Scaling scales computing resources in response to changes in business load. A scheduled task is a type of scaling task that can execute a specified scaling rule at a specified time. By creating a scaling rule that removes 1 ECS instance from the scaling group, and creating a scheduled task that executes this scaling rule every night at 00:00, you can achieve the desired result. You do not need to create a new scaling group, because you already have one scaling group created. You also do not need to create an event-triggered task, because this type of scaling task is triggered by events such as Cloud Monitor alarms or API calls, not by a specific time. References: 1, 2, and 3.

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. 

In Alibaba Cloud SLB, Layer-7 (HTTP/HTTPS) services require enabling the "X-Forwarded-For" header to retrieve the real IP address of clients, while Layer-4 (TCP/UDP) services can obtain the real IP address directly without additional settings.

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Alibaba Cloud CDN is particularly effective for websites with high traffic and static resources that are frequently accessed by different users. In such cases, CDN caching and delivery from edge nodes greatly reduce the load on origin servers and improve access speed for end users, especially in regions closer to the edge nodes.

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

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

According to the Alibaba Cloud Auto Scaling documentation1, the Lifecycle Hook feature allows you to perform custom operations on instances that are added to or removed from a scaling group. You can define a lifecycle hook to specify a timeout period and a web hook URL. When an instance is about to be removed, Auto Scaling sends a notification to the web hook URL and waits for a response. During the timeout period, you can perform the necessary operations on the instance, such as gracefully shutting down the service, backing up the data, or sending a custom notification. After the operations are completed, you can send a response to the web hook URL to confirm the removal of the instance. This way, you can ensure that the instance is removed without affecting the user experience or causing data loss. Therefore, option D is the best solution to eliminate the customer’s concern. References: Lifecycle hooks and Alibaba Cloud Auto Scaling.

According to the Alibaba Cloud Academy, a VPC is an isolated network environment that is completely isolated from each other. Each VPC has an independent tunnel ID, and a tunnel ID corresponds to a virtualized network. This means that different VPCs cannot communicate with each other through the tunnel ID. Subnets are not divided like the traditional network environment, but rather are logical divisions of the VPC. Different cloud servers within each subnet are connected by the same router, but different subnets are interconnected by route tables, not switches. ECS instances in a VPC use security group firewalls for Layer 4 network access control, not Layer 2. The internal networks of different VPCs are completely isolated and can be interconnected through IP addresses mapped to the outside, such as NAT Gateway or EIP. References: ACP Cloud Computing Certification Preparation Course - Internetworking with VPC, Alibaba Cloud VPC User Guide

Data Transmission Service (DTS) is a real-time data streaming service that supports data transmission between data sources such as relational databases, NoSQL, and Big Data (OLAP). DTS supports data migration, data synchronization, and change data subscription scenarios. DTS can migrate your data to and from most of the widely used commercial and open source databases. It supports homogeneous migrations such as MySQL to MySQL, as well as heterogeneous migrations between different database platforms, such as Oracle to MySQL. Migrations can be from on-premises databases to RDS or ECS, databases running on ECS to RDS, or vice versa, as well as from one RDS database to another RDS database. DTS also supports database schema replication between instances, which means that DTS can automatically create the same schema as the source database in the target database. DTS also supports warning when source and destination has some unresolved conflict found, such as data type mismatch, primary key conflict, or foreign key constraint violation. DTS can help you resolve these conflicts by providing suggestions or allowing you to modify the data mapping rules. Therefore, the correct answer is C. Supports all of the above functions. References:

1: Data Transmission Service - Alibaba Cloud

2: What is Data Transmission Service? - Alibaba Cloud

3: Database Migration - AlibabaCloud

4: Cloud Migration without Stopping Services: Alibaba Cloud DTS

When using Alibaba Cloud SLB, you can set different weights for backend ECS instances. The higher the weight of a backend ECS instance, the more load will be assigned to it. However, the load distribution is not based on the absolute value of the weight, but on the proportion of the weight in the total weight of all healthy backend ECS instances. For example, if there are two healthy backend ECS instances with weights of 100 and 200 respectively, the first instance will receive 33.3% of the load, and the second instance will receive 66.7% of the load. Therefore, to determine the load distribution of the 5 ECS instances in the question, we need to know the weight settings of the remaining 4 ECS instances. Without this information, we cannot tell what would happen. The other options are incorrect because they are based on wrong assumptions or misunderstandings of the SLB weight setting mechanism. 

There is no limit on the number of objects that can be stored in a single OSS bucket in Alibaba Cloud. OSS is designed to support massive data storage, allowing users to store an unlimited number of files within a bucket. The only limitations are the bucket storage capacity and account-level quotas.

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RDS accounts can be used to connect with the databases created on a given RDS instance. Each account can be bound with multiple databases. However, the read/write permissions of each database can be assigned to multiple RDS accounts, not just one. For example, you can create an account with read-only permission for all databases, and another account with read-write permission for a specific database. This way, you can manage the access control of your databases more flexibly and securely. References:  Introduction to ApsaraDB RDS - Alibaba Cloud Document Center - User Management - Account Permissions

Public cloud computing offers advantages such as rapid deployment, increased flexibility and scalability, reduced costs associated with infrastructure, and minimized management and maintenance efforts. Option E is incorrect, as cloud providers typically manage the underlying infrastructure, and users do not have full control over it. Cloud computing abstracts the infrastructure layer, allowing users to focus on applications without needing to manage physical resources.

Alibaba Cloud Express Connect is a service that enables high-bandwidth, reliable, secure, and private connections between different networks, such as VPC networks across regions, Alibaba Cloud accounts, and on-premise data centers1. It supports different connection methods, such as physical connections, virtual border routers, and Express Cloud Connect1.

Scenario A: Intranet communication between VPCs and Smart Access Gateway in customers different branch offices. This scenario can be achieved by using Express Cloud Connect, which is based on the hardware capacities of Smart Access Gateway and provides SD-WAN capabilities1. Express Cloud Connect allows you to connect your branch offices to Alibaba Cloud through a dedicated partner backbone network, and access VPC networks in all regions1.

Scenario B: Intranet communication between a VPC and servers in an external IDC. This scenario can be achieved by using physical connections, which are dedicated network connections between on-premise data centers and VPC networks1. You can lease a line from your ISP or work with an Alibaba Cloud partner to establish a physical connection to Alibaba Cloud1. This way, you can access VPC networks in all regions with high bandwidth and low latency1.

Scenario C: Intranet communication between two VPCs in different accounts and different CIDR Blocks. This scenario can be achieved by using peering connections, which are logical connections that enable communication between VPC networks2. Peering connections support cross-region and cross-account scenarios, and allow you to connect VPC networks with different CIDR blocks2. However, peering connections are not part of Alibaba Cloud Express Connect, but a separate service called Cloud Enterprise Network2.

Scenario D: Intranet communication between two VPCs under the same account in the same region. This scenario can also be achieved by using peering connections, which are logical connections that enable communication between VPC networks2. Peering connections support intra-region and same-account scenarios, and allow you to connect VPC networks with different CIDR blocks2. However, peering connections are not part of Alibaba Cloud Express Connect, but a separate service called Cloud Enterprise Network2. References: 1: Express Connect - Alibaba Cloud 2: Introduction to Cloud Enterprise Network - Alibaba Cloud Document 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.

This is a correct description of distributed computing, where a large task is divided into smaller tasks, distributed across multiple nodes, and later recombined to produce the final result. Distributed computing is widely used to handle large-scale computations and improve processing efficiency.

Alibaba Cloud OSS does not charge for data ingress, meaning there are no traffic charges for uploading files to OSS, whether through the management console or Open API. However, traffic charges may apply for data egress, i.e., downloading files from OSS.

CEN is a service that allows you to create a global network for rapidly building a distributed business system with a hybrid cloud computing solution. CEN enables you to build a secure, private, and enterprise-class interconnected network between VPCs in different regions and your local data centers1. CEN uses transit routers deployed in different regions to build a full-mesh network on top of the Alibaba Cloud global transmission network. CEN enables global network communication: The two transit routers can be connected through multiple highly available and highly reliable lines2. To establish communication between two VPCs in different regions via the intranet, you can use CEN to attach the VPCs to the transit routers in their respective regions, and then create a bandwidth plan to allocate bandwidth resources for inter-region connections3. This way, you can avoid the complexity and cost of setting up VPN or Express Connect connections between the VPCs, and enjoy the benefits of CEN, such as large-scale and on-demand networking, simplified network topology, flexible management, globally connected network, shortest-path algorithm, high redundancy, automatic route learning and advertisement, and bandwidth sharing and management2. References: Introduce Cloud Enterprise Network CEN and how … - Alibaba Cloud Academy, Cloud Enterprise Network (CEN) - Alibaba Cloud, Attach a network instance to a CEN instance - Cloud Enterprise Network - Alibaba Cloud

To prevent frequent alerts when User A logs in from Shanghai, the best solution is to configure the Security Center to recognize Shanghai as a frequent login location. This will prevent unnecessary security alerts each time User A accesses the server from this location.

By default, ECS instances in different zones within the same region are not interconnected via the Intranet. To enable communication between instances across zones, you would need to configure a VPC or use other network configurations. This setup provides isolation and flexibility in managing network traffic within different zones.

A route table is a set of rules that determine how network traffic is routed within a VPC or between different network instances1. A VRouter is a hub that connects all VSwitches in the same VPC and enables communication between them2. When you create a VPC, a VRouter and a default route table are automatically created for the VPC1. The default route table contains system routes that are automatically generated by the system based on the network topology1. The system routes cannot be modified or deleted1.

However, you can also create custom route tables for your VPC and add custom routes to them1. Custom routes are manually configured by users to route traffic to specific destinations, such as other VPCs, VBRs, VPN Gateways, or NAT Gateways1. Custom routes can be modified or deleted as needed1. You can also associate VSwitches with different route tables to implement fine-grained routing control1.

Therefore, the statement that the routing entries of the route table can not be modified manually is not correct, as it only applies to system routes, not custom routes. The other statements are correct, as each VRouter may have multiple route tables, one default and several custom1; when a VPC is deleted, the corresponding route table is also deleted3; and the default route table cannot be deleted1. References: Route table overview - Virtual Private Cloud - Alibaba Cloud Documentation Center, VRouter overview - Virtual Private Cloud - Alibaba Cloud Documentation Center, Delete a VPC - Virtual Private Cloud - 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