Configure 301/302 redirection - - Alibaba Cloud Documentation Center

The 301/302 redirection feature supports HTTP 301 and 302 status codes that are returned by the origin server. All features that are supported by the HTTP 302 status code in this topic are supported by the HTTP 301 status code. After you configure 301/302 redirection, points of presence (POPs) process the HTTP 301 or 302 status code that is returned by the origin server instead of returning the status code to clients. This simplifies request processing and accelerates content delivery.

Prerequisites

301/302 redirection is enabled on the origin server.

Background information

301 and 302 are HTTP status codes, which indicate that an existing resource is relocated and the request failed to access the resource. In most cases, servers add the Location header to the response header to resolve this issue. After a client receives a response that carries the HTTP 301 or 302 status code and the Location header, the request is redirected to the address that is specified by the Location header to retrieve the resource.

How it works

If a POP redirects a request to an origin server and receives the HTTP 301 or 302 status code from the origin server, the POP processes the status code. The request is redirected to the address that is specified by the Location header returned from the origin server to retrieve the resource. In this case, the HTTP 301 or 302 status code is not returned to the client.

A user requests http://example.com/examplefile.txt from a POP.
The requested file is not cached on the POP. The POP redirects the request to the origin server.
The origin server receives the request and returns the HTTP 301 or 302 status code. The response header carries the Location header that specifies the address http://www.example.org/examplefile.txt.
The POP receives the response and redirects the request to http://www.example.org/examplefile.txt.
The POP retrieves and caches the file.
The POP returns the retrieved file to the user.

If other users request http://example.com/examplefile.txt, the requested file is served directly from the POP.

Usage notes

Before you configure 301/302 redirection for an accelerated domain name, check whether an origin host is configured for the domain name. For more information, see Configure an origin host.

If an origin host is not configured for the domain name: When the origin server returns the HTTP 301 or 302 status code and the Location header that specifies a URL to the POP, the request is redirected to the URL that is specified by the Location header. The value of the Host header in the request is the domain name that is specified by the Location header.
If an origin host is configured for the domain name: When the origin server returns the HTTP 301 or 302 status code and the Location header that specifies a URL to the POP, the value of the Host header in the request is the Host header that is configured for the accelerated domain name. By default, the Host header value is the accelerated domain name. If you use the domain name that is specified by the Location header as the value of the Host header in the back-to-origin request, an error occurs. If you want DCDN to support this scenario, submit a ticket.
The Location header that is returned from the origin server can be in the following formats:
- Location: http://www.example.net/index.html. The POP redirects the request to the full URL specified by the Location header.
- Location: //www.example.net/index.html. The POP redirects the request to the URL that includes the protocol that the original request uses and the value of the Location header.
- Location: /index.html. The POP redirects the request to the URL that includes the protocol and domain name that the original request uses and the value of the Location header.

Procedure

Log on to the DCDN console.
In the left-side navigation pane, click Domain Names.
On the Domain Names page, find the domain name whose acceleration region you want to change and click Configure.
In the left-side navigation pane of the domain name, click Origin Fetch.
On the Origin Fetch tab, find 301/302 Redirection.
Turn on 301/302 Redirection.

Click Modify and configure the parameters. The following table describes the parameters.

Parameter	Description
Maximum Number of Redirects	Specify the maximum number of times that a POP can redirect to the URL that is specified by the Location header for each request. If the maximum value is exceeded, the HTTP 301 or 302 status code is returned to the user. Valid values: 1 to 5. Default value: 2. Note The maximum number of 301/302 redirects determines the number of back-to-origin requests that can be redirected to the origin server by a POP. Maximum number of back-to-origin requests = Maximum number of 301/302 redirects + 1. In this case, the default maximum number of back-to-origin requests is 3. Valid values: 2 to 6.
Retention Request Parameters	Yes: In 301/302 redirects, the parameters in requests that are redirected to the origin server are retained. The request parameters are passed to the server that is specified by the Location header. No: In 301/302 redirects, the parameters in requests that are redirected to the origin server are not retained.
Retain Request Headers	Yes: In 301/302 redirects, the headers in requests that are redirected to the origin server are retained. The header parameters are passed to the server that is specified by the Location header. No: In 301/302 redirects, the headers in requests that are redirected to the origin server are not retained.

Click OK.