Web Application Firewall：Enable WAF protection for a Layer 7 CLB instance

Background information

After you add Elastic Compute Service (ECS) instances that are deployed in the same region to a CLB instance, CLB uses virtual IP addresses (VIPs) to combine the ECS instances into a high-performance, high-availability server pool. Then, CLB forwards inbound requests to the ECS instances based on forwarding rules. For more information, see What is CLB?

You can add a Layer 7 CLB instance to WAF. After you add a Layer 7 CLB instance to WAF, all traffic of the CLB instance is redirected to WAF by using a specified gateway. WAF filters out malicious traffic and forwards normal traffic to the CLB instance. The following figure shows the network architecture.

Limits

Web services that use one of the following Alibaba Cloud services can be added to WAF in cloud native mode: Application Load Balancer (ALB), Microservices Engine (MSE), Function Compute, Classic Load Balancer (CLB), Elastic Compute Service (ECS), and Network Load Balancer (NLB).. If you want to use WAF to protect web services that do not use the preceding Alibaba Cloud services, add the domain names of the web services to WAF in CNAME record mode. For more information, see Add a domain name to WAF.

Prerequisites

• A WAF 3.0 instance is purchased. For more information, see Purchase a subscription WAF 3.0 instance and Purchase a pay-as-you-go WAF 3.0 instance.

• A CLB instance is created, and an HTTP or HTTPS listener is added to the CLB instance. The instance also meets the preceding requirements. For more information about the requirements, see the "Limits" section of this topic. For more information about how to add an HTTP or HTTPS listener, see Add an HTTP listener or Add an HTTPS listener.

• If you use a subscription WAF instance, make sure that the number of protected objects that you added to WAF does not exceed the upper limit. If the number exceeds the upper limit, you can no longer add cloud service instances to WAF.

  To view the number of protected objects that you can add to WAF, go to the Protected Objects page.

Add traffic redirection ports

1. Log on to the WAF 3.0 console. In the top navigation bar, select the resource group and region of the WAF instance. You can select Chinese Mainland or Outside Chinese Mainland.

2. In the left-side navigation pane, click Website Configuration.

3. On the Cloud Native tab, click CLB(HTTP/HTTPS) in the left-side cloud service list.

4. Click Add.

5. Click Authorize Now to authorize your WAF instance to access CLB.

   Alibaba Cloud automatically creates the AliyunServiceRoleForWAF service-linked role. To view the service-linked role, log on to the Resource Access Management (RAM) console and choose Identities > Roles in the left-side navigation pane.

   Note

   If your WAF instance is already authorized to access CLB, skip this step.

6. In the Configure Instance - Layer 7 CLB Instance panel, configure the parameters. The following table describes the parameters.

   

   Parameter	Operation
   Select the instance and port to be added.	Synchronize Instances If the instance that you want to add to WAF is not in the instance list, click Synchronize Instances to refresh the instance list. Add Port Find the instance that you want to add to WAF and click Add Port in the Actions column. Select the HTTP or HTTPS ports that you want to add and click OK. Important If you want to add an HTTPS port, make sure that the certificate that is configured for the port is purchased by using Alibaba Cloud Certificate Management Service or uploaded to Certificate Management Service. Otherwise, the instance may fail to be added to WAF. For more information, see What do I do if an error message indicating that the certificate is incomplete is displayed when I add an HTTPS port for traffic redirection? If a certificate that is configured for a port of the instance has expired or was manually uploaded in the CLB console, certificates cannot be synchronized to WAF. You must replace the certificate with a new certificate that is purchased by using Certificate Management Service or uploaded to Certificate Management Service.
   Whether Layer 7 Proxy, Such as Anti-DDoS Pro, Anti-DDoS Premium, or Alibaba Cloud CDN, Is Deployed in Front of WAF	Specify whether a Layer 7 proxy, such as Anti-DDoS Proxy and Alibaba Cloud CDN, is deployed in front of WAF. By default, No is selected. This value specifies that WAF receives requests that are sent from clients. The requests are not forwarded by proxies. Note When a request is sent from a client to WAF, WAF uses the IP address that is used to establish the connection to WAF as the IP address of the client. The IP address is specified by the REMOTE_ADDR field of the request. If a Layer 7 proxy is deployed in front of WAF, select Yes. This value specifies that WAF receives requests that are forwarded to WAF by a Layer 7 proxy. To ensure that WAF can obtain the actual IP addresses of clients for security analysis, you must configure the Obtain Actual IP Address of Client parameter. Use the First IP Address in X-Forwarded-For Field as Actual IP Address of Client (default) By default, WAF uses the first IP address in the X-Forwarded-For field as the IP address of a client. [Recommended] Use the First IP Address in Specified Header Field as Actual IP Address of Client to Prevent X-Forwarded-For Forgery If you use a proxy that contains the originating IP addresses of clients in a custom header field, such as X-Client-IP or X-Real-IP, select this value. Then, enter the custom header field in the Header Field field. Note We recommend that you use custom header fields to store the originating IP addresses of clients and specify the header fields in WAF. This way, attackers cannot forge the X-Forwarded-For field to bypass WAF inspection. This improves the security of your business. You can enter multiple header fields. Press the Enter key each time you enter a header field. If you enter multiple header fields, WAF reads the header fields in sequence until it obtains the IP address of a client. If WAF cannot obtain the IP address of a client from the header fields, WAF uses the first IP address in the X-Forwarded-For field as the IP address of the client.
   Resource Group	Select the resource group to which you want to add the CLB instance. If you do not select a resource group, the instance is added to the default resource group. Note You can use Resource Management to create resource groups and manage resources within your Alibaba Cloud account by department or project. For more information, see Create a resource group.
   Advanced Settings	Obtain the listening protocol of WAF by using the X-Forwarded-Proto header field The X-Forwarded-Proto header field is automatically added to HTTP requests. The X-Forwarded-Proto header field is used to identify the original protocol used by the client. If your website cannot correctly handle the X-Forwarded-Proto header field, compatibility issues may occur and your business may be affected. To prevent such issues, clear Obtain the listening protocol of WAF by using the X-Forwarded-Proto header field. Enable Traffic Mark If you select Enable Traffic Mark, requests that pass through WAF are marked. This helps origin servers obtain the originating IP addresses or ports of clients. If an attacker obtains information about your origin server before you add your domain name to WAF and uses another WAF instance to forward requests to the origin server, you can select Enable Traffic Mark to intercept malicious traffic. The origin server checks whether the requests passed through WAF. If the specified header fields exist in a request, the request passed through WAF and is allowed. If the specified header fields do not exist in a request, the request did not pass through WAF and is blocked. You can configure the following types of header fields: Custom Header If you want to add a custom header field, you must configure the Header Name and Header Value parameters. WAF adds the header field to the back-to-origin requests. This allows the origin server to check whether requests passed through WAF, collect statistics, and analyze data. For example, you can add the ALIWAF-TAG: Yes custom header field to mark the requests that pass through WAF. In this example, the name of the header field is ALIWAF-TAG and the value of the header field is Yes. Originating IP Address You can specify a header field that records the originating IP addresses of clients. This way, your origin server can obtain the originating IP addresses of clients. For more information about how WAF obtains the originating IP addresses of clients, see Whether Layer 7 Proxy, Such as Anti-DDoS Pro, Anti-DDoS Premium, or Alibaba Cloud CDN, Is Deployed in Front of WAF. Source Port You can specify a header field that records the originating ports of clients. This way, your origin server can obtain the ports of clients. Important We recommend that you do not configure a standard HTTP header field, such as User-Agent. Otherwise, the original value of the standard header field is overwritten by the value of the custom header field. You can click Add Mark to add a header field. You can specify up to five header fields. Back-to-origin Keep-alive Requests If the persistent connections between WAF and your origin server time out, you can reconfigure the timeout period of persistent connections, the number of reused persistent connections, and the timeout period of idle persistent connections. Read Connection Timeout Period: the amount of time during which WAF waits for a response from the origin server. After the timeout period ends, WAF closes the connection. Valid values: 1 to 3600. Default value: 120. Unit: seconds. Write Connection Timeout Period: the amount of time during which WAF waits for a request to be forwarded to the origin server. After the timeout period ends, the origin server closes the connection. Valid values: 1 to 3600. Default value: 120. Unit: seconds. Back-to-origin Keep-alive Requests: If you want to configure the number of reused persistent connections or the timeout period of idle persistent connections, turn on Back-to-origin Keep-alive Requests and configure the following parameters: Reused Keep-alive Requests: the number of requests that WAF can forward to the origin server or the number of responses that WAF can receive from the origin server at the same time. Valid values: 60 to 1000. Default value: 1000. Timeout Period of Idle Keep-alive Requests: the timeout period of idle persistent connections. Valid values: 10 to 3600. Default value: 3600. Unit: seconds.

7. Select the instance that you want to add to WAF and click OK.

   After you add a CLB instance to WAF, the CLB instance automatically becomes a protected object of WAF. The name of the protected object is in the following format: Instance ID-Port-Asset type. Basic protection rules are automatically enabled for the protected object. You can configure protection rules for the protected object on the Protected Objects page. To go to the Protected Objects page, click the ID of the CLB instance that you added to WAF on the Cloud Native tab of the Website Configuration page. For more information, see Protection configuration overview.

Manage WAF protection

Manage WAF protection in the WAF console

1. Log on to the WAF 3.0 console. In the top navigation bar, select the resource group and region of the WAF instance. You can select Chinese Mainland or Outside Chinese Mainland.

2. In the left-side navigation pane, click Website Configuration.

3. Manage WAF protection.

   • On the Cloud Native tab, click CLB(HTTP/HTTPS) in the left-side cloud service list. Then, you can view CLB instances that are added to WAF.

   • View protected objects and configure protection rules.

     After you add a CLB instance to WAF, the instance automatically becomes a protected object of WAF. The name of the protected object contains the -clb7 suffix and basic protection rules are automatically enabled for the protected object. You can view and configure protection rules for the protected object on the Protected Objects page. To go to the Protected Objects page, click the instance ID on the Cloud Native tab of the Website Configuration page. For more information, see Protection configuration overview.

   • View origin servers and remove a CLB instance from WAF.

     After you add a CLB instance to WAF, you can view the protection details of the origin servers and disable traffic redirection or remove traffic redirection ports in emergency disaster recovery scenarios.

     • Click the icon to the left of the instance name and view the ports that are added to WAF.

     • View port details: Click Port Details to view information about the port, protocol, and certificate, and then configure the Whether Layer 7 Proxy, Such as Anti-DDoS Pro, Anti-DDoS Premium, or Alibaba Cloud CDN, Is Deployed in Front of WAF, Enable Traffic Mark (Advanced Settings), and Back-to-origin Keep-alive Requests (Advanced Settings) parameters.

     • Remove a traffic redirection port: Find the port that you want to remove from WAF and click Remove in the Actions column. In the Remove message, click OK.

       Important

       • When you remove a traffic redirection port from WAF, traffic on the port is no longer protected by WAF. To re-add the traffic redirection port to WAF, click Add. For more information, see Add traffic redirection ports.

       • After you remove a traffic redirection port from WAF, your web services may be interrupted for several seconds. If clients can be automatically reconnected, the web services automatically resume. Configure reconnection mechanisms and back-to-origin settings based on your business requirements.

FAQ

• How do I check whether WAF protection is enabled for a Layer 7 CLB instance?

  1. Enter the domain name that you added to WAF in the address bar of a browser. If the domain name can be accessed, the domain name is protected by WAF.

  2. Insert malicious SQL code, such as xxx.xxxx.com?id=1 and 1=1, into requests and check whether the requests are blocked. If the 405 Method Not Allowed error is returned, the requests are blocked.

     

• CLB supports Layer 4 and Layer 7 listeners. Layer 4 listeners use the TCP or UDP protocol, and Layer 7 listeners use the HTTP or HTTPS protocol.

  • Layer 4 listeners directly forward requests to backend servers. When a CLB instance receives a request, the CLB instance modifies the destination IP address and destination port of the data packet based on the listener port. Then, the CLB instance forwards the request to a backend server. A TCP connection is established between the client and the backend server.

  • A Layer 7 listener functions as a reverse proxy. After a client request reaches a Layer 7 listener of CLB, CLB establishes a new TCP connection to a backend server over HTTP, instead of directly forwarding the request to the backend server. Compared with Layer 4 listeners, Layer 7 listeners require an additional step of Tengine processing. Factors such as client port exhaustion or excessive workloads on backend servers may affect the throughput capacity of Layer 7 listeners. If your business requires higher performance, we recommend that you use Layer 4 listeners.

  For more information, see CLB listener overview.

• Can I add an HTTP port and an HTTPS port to WAF when I enable WAF protection for a layer 7 CLB instance?

  Yes, you can add an HTTP port and an HTTPS port.

• What do I do if the "The CLB certificate whose port number is 443 is incomplete. Go to the SLB console and select a certificate that is from Certificate Management Service." error message appears when I enable WAF protection for a layer 7 CLB instance?

  You must log on to the Certificate Management Service console to renew or upload the certificate and then select the certificate in the CLB console. For more information, see Certificate renewal or Upload an SSL certificate.

References

• For information about how to obtain the originating IP addresses of clients, see Enable Layer 7 listeners to preserve client IP addresses.

• For information about how to troubleshoot the issue that CLB or ECS instances are not displayed on the Website Configuration page, see Why am I unable to find the CLB or ECS instance that I want to add to WAF on the Website Configuration page?