Rewrite HTTP headers in back-to-origin requests

Alibaba Cloud CDN allows you to rewrite HTTP headers in back-to-origin requests. You can add, delete, change, and replace HTTP headers in back-to-origin requests based on your business requirements.

Background information

HTTP request headers are a component of the header section in request messages transmitted over HTTP. HTTP request headers bring specific parameters to servers.

If the requested resource is not cached on CDN nodes, the request is redirected to the origin server. The information carried by the request headers is passed to the origin server. Alibaba Cloud CDN allows you to rewrite HTTP headers in back-to-origin servers so that your origin server can identify user information more easily. For example, you can set the X-Forward-For header to bring real client IP addresses to your origin server.

Note

• A back-to-origin request is an HTTP message that is transmitted by Alibaba Cloud CDN to the origin server of a specific accelerated domain name. A rewrite rule rewrites only HTTP headers in HTTP requests that are transmitted between an origin server and CDN nodes. It does not rewrite HTTP headers in HTTP requests that are transmitted between CDN nodes and clients.
• You cannot configure custom HTTP request headers for wildcard domain names.

1. Log on to the Alibaba Cloud CDN console.
2. In the left-side navigation pane, click Domain Names.
3. On the Domain Names page, find the domain name that you want to manage and click Manage in the Actions column of the domain name.
4. In the management pane of the domain name, click Back-to-origin.
5. Click the Custom Request Headers (New) tab.
6. Click Customize.
7. Set the parameters in the Back-to-origin Request Headers dialog box.
   Notice If different operations are performed on the same request header at the same time, these operations have different priorities. The operations are prioritized in the following descending order: Replace > Add > Change or Delete. For example, if you perform the Add and Delete operations on the same request header at the same time, the request header is added and then deleted.

   • Parameters of the Add operation

     Parameter	Example	Description
     Operation	Add	Adds a specific request header to back-to-origin HTTP requests.
     Request Header	Custom Back-to-origin Request Headers	You can use the default value, or select Custom Back-to-origin Request Headers from the Request Header drop-down list to specify a request header.
     Header Name	x-code	The name of the custom request header is x-code.
     Header Value	key1, key2	You can specify one or more values for a request header. Separate values with commas (,).
     Allow Duplicates	Yes	Yes: You can add duplicate request headers. For example, x-code:key1 and x-code:key2 can coexist. No: The latest header value overwrites the existing one that uses the same header name. For example, if you add x-code:key1 and then add x-code:key2, the final header key-value pair is x-code:key2.

   • Parameters of the Delete operation

     Parameter	Example	Description
     Operation	Delete	Deletes the values of all specified request headers. Duplicate headers are also deleted.
     Request Header	Custom Back-to-origin Request Headers	You can use the default value, or select Custom Back-to-origin Request Headers from the Request Header drop-down list to specify a request header.
     Header Name	x-code	The name of the custom request header is x-code.

   • Parameters of the Change operation

     Parameter	Example	Description
     Operation	Change	You can perform the Change operation only if no duplicate request headers exist.
     Request Header	Custom Back-to-origin Request Headers	You can use the default value, or select Custom Back-to-origin Request Headers from the Request Header drop-down list to specify a request header.
     Header Name	x-code	The name of the custom request header is x-code.
     Change Value To	key1, key3	You can specify one or more values for a request header. Separate values with commas (,).

   • Parameters of the Replace operation

     Parameter	Example	Description
     Operation	Replace	You can perform the Replace operation only if no duplicate request headers exist.
     Request Header	Custom Back-to-origin Request Headers	You can use the default value, or select Custom Back-to-origin Request Headers from the Request Header drop-down list to specify a request header.
     Header Name	x-code	The name of the custom request header is x-code.
     Find	key	Allows you to use regular expressions to search for the value that you want to replace.
     Replace With	abc	Allows you to use regular expressions to replace matching values.
     Match	Match All	Match All: All matching values are replaced. For example, if you use a regular expression to replace all the "key" in x-code:key1,key2,key3 with "abc", the key-value pair is changed tox-code:abc1,abc2,abc3. Match the First Only: Only the first matching value is replaced. For example, if you use a regular expression to replace the first "key" in x-code:key1,key2,key3 with "abc", the key-value pair is changed to x-code:abc1,key2,key3.

8. Click OK.