HTTPDNS:Configure custom DNS resolution based on Function Compute

Prerequisites

• You have added the domain name for which you want to configure custom DNS resolution. For more information, see 1. Add a domain name.

1. Authorize the service-linked role

When HTTPDNS calls Function Compute to implement custom DNS resolution, you must grant permissions to a service-linked role in the HTTPDNS console so that HTTPDNS can use Function Compute.

2. Create a custom resolution function

First, activate Alibaba Cloud Function Compute and develop a custom resolution function. After development, publish the service and function, and then generate a formal version or alias.

To ensure the security and stability of the HTTPDNS Function Compute policy, do not use the default Latest version when you configure the policy. You must specify a published service and function version.

HTTPDNS supports both FC 2.0 and FC 3.0, but FC 3.0 is recommended (FC 2.0 is deprecated). For more information about the differences between them, see Differences between FC 2.0 and FC 3.0.

If you still need to create an FC 2.0 function, see Create an FC 2.0 function.

3. Write the custom resolution function code

1. Write the function code

   In the function editor, enter your custom resolution logic. The function must accept context parameters passed by HTTPDNS, such as client IP, region, and ISP, and return the processed resolution result. For example:

   The programming language in this example is nodejs6 or nodejs8.

   'use strict';
   exports.handler = (event, context, callback) => {
     // Format the input parameters into an object.
     const eventObj = JSON.parse(event.toString());
     const {
       location, // Region
       ips, // Resolution result from the authoritative server
       ttl, // Original TTL
     } = eventObj;
   
     if (location.province === 'zhejiang' && location.isp === 'chinanet') {
       // When a user from Zhejiang Telecom accesses the domain name, return the specified IP address.
       callback(null, {
         ips: ips.concat(['1.1.X.X']), // Add the specified IP address to the returned IP array.
         ttl: event.ttl * 2, // Modify the TTL.
         extra: "", // Carry additional parameters for the client.
       });
     } else {
       // Default return.
       callback(null, {
         ips,
         ttl,
         extra: "",
       });
     }
   };

2. Configure test input parameters

   Before you click Test Function, set mock input parameter data to verify that the function behaves as expected. The test event must simulate the actual HTTPDNS call format. For example:

   {
     "domainName": "www.aliyun.com", // The domain name being resolved
     "clientIp": "192.168.1.4", // Client IP
     "location": {
       "continent": "asia", // Continent of the client IP
       "region": "cn", // Country or region of the client IP
       "isp": "bgp", // ISP line of the client IP 
       "province": "zhejiang" // Province of the client IP
     },
     "ips": ["192.168.1.3"], // List of resolution results. This result is not available in the BEFORE_READ_CACHE stage.
     "ttl": 60, // TTL of the resolution result. This result is not available in the BEFORE_READ_CACHE stage.
     "hookType": "BEFORE_WRITE_CACHE", // Stage in which the function runs
     "parameters":{ // Parameter object carried in the resolution request
       "param1":"p1",   // Corresponds to the parameter "sdns-param1=p1" in the URL
       "param2":"p2"
      }
   }

3. Run the test and verify the result

   Click Test Function and check whether the returned result contains the expected ips, ttl, or extra fields and is in the correct format. Example response:

   {
       "ips": event.ips.concat(['192.168.1.2']),
       "ttl": event.ttl * 2,
       "extra": "some-thing-send-to-user"
       // ,"domainName": "www.alibabacloud.com" // Valid only in the BEFORE_READ_CACHE stage
       // ,"cacheKey": "cache-key-001" // Valid only in the BEFORE_READ_CACHE and BEFORE_WRITE_CACHE stages
    }

   Note

   For more information about the custom resolution function mechanism and complete descriptions of input and response parameter fields, see the detailed documentation: Write the custom resolution function code.

4. Attach the Function Compute service to the domain name for resolution

For each domain name that requires custom resolution, you can configure Function Compute services in multiple regions. You can also configure the same Function Compute service for the Function Compute policies of multiple domain names that require custom resolution.

What to do next

After you configure custom DNS resolution based on Function Compute as described in this topic, see Overall workflow to complete the subsequent steps.