CDN:Rewrite access URLs

Background information

The HTTP status code 302, also known as the Found message, indicates that the requested resource has temporarily relocated. After you configure the access URL rewrite feature, POPs add the new URL of the resource to the Location header in the response that is returned together with an HTTP 302 status code. After the client receives the response, the client sends a request to the new URL.

After you create an access URL rewrite rule, the POPs return the HTTP status code 302 to the client by default if the requested resource has relocated. You can also set the HTTP status code to 303 or 307. To change the HTTP status code, submit a ticket.

Differences between access URL rewrite and origin URL rewrite

Rewrite an access URL

1. A client initiates a request to a POP. The request URL is old.example.com/hello.

2. After the POP receives the request, the POP adds the new URL to the HTTP Location header in the response that is returned together with an HTTP 302 status code, and rewrites the request URL to new.example.com/hello based on access URL rewrite rules.

3. After the client receives the response and the HTTP 302 status code, the client initiates a request to the new URL.

4. The POP checks the cache. If the content that corresponds to the rewritten URL exists in the cache, the POP returns the content to the client. If not, the POP initiates a request to the origin server. The request URL is new.example.com/hello, which is rewritten.

5. The origin server receives the request and returns the requested content to the POP.

6. The POP caches the requested content and returns the requested content to the client.

Rewrite an origin URL

1. A client initiates a request to a POP. The request URL is cdn.example.com/files/hello.txt.

2. After the POP receives the request, the POP checks the cache. If the content that corresponds to the rewritten URL exists in the cache, the POP returns the content to the client. If not, the POP rewrites the origin URL to origin.example.com/secret/files/hello.txt based on origin URL rewrite rules.

3. The origin server receives the request and returns the requested content to the POP.

4. The POP caches the requested content and returns the requested content to the client.

Procedure

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.

4. In the left-side navigation tree of the domain name, click Cache.

5. Click the Access URL Rewrite tab.

6. Click Create, and configure the parameters based on your business requirements.

   

   Parameter	Description
   Path to Be Rewritten	Enter a URL that starts with a forward slash (/). The URL cannot contain http:// or domain names. You can use Perl Compatible Regular Expressions (PCRE) to specify the URL. Example: ^/hello$.
   Target Path	Enter a URL that starts with a forward slash (/). The URL cannot contain http:// or domain names. Example: /index.html.
   Flag	By default, Redirect and Break are supported. Redirect: If the URL in a request matches a rule, Alibaba Cloud CDN returns the HTTP 302 status code and the request is redirected to the actual URL. The value of the Location header in the response message that is returned by the POP to the client is the actual URL. Parameters in the original URL are not modified. After the current rule is executed, the request is matched against other rules. Break: If the URL in a request matches a rule, the requested URL is overwritten by the actual URL. Parameters in the original URL are not modified. After the current rule is executed, other rules are skipped. Empty, enhance-break, and enhance_redirect are also supported. To use these rules, submit a ticket. Empty: If multiple rules are configured and the URL in a request matches a rule, the request is matched against other rules after the current rule is executed. enhance_break: enhance_break is similar to Break, but modifies the URL, including parameters. enhance_redirect: enhance_redirect is similar to Redirect, but modifies the URL, including parameters. Note Different rules use different rewrite methods, and whether the rewritten URL supports other domain names and other protocols also varies. Empty, Break, and enhance_break rewrite the URL in a request, but cannot modify the domain name or protocol in the URL. For example, the rules cannot modify the protocol from HTTP to HTTPS. Redirect and enhance_redirect use 302 redirection to rewrite a URL, and can modify the domain name or protocol in the URL. You can set the Location header to the current domain name or another domain name. This way, the original URL uses the example.com domain name, and the rewritten URL uses the aliyundoc.com domain name. The Location header in 302 redirection responses supports different protocols. This way, the original URL uses the HTTP protocol, and the rewritten URL uses the HTTPS protocol.
   Rule Condition	Rule conditions can identify parameters in a request to determine whether a configuration applies to the request. Do not use conditions Select the configured rule conditions in Rules Engine. For more information, see Rules engine.
   Enable NGINX variable computing	By default, the check box is not selected. If you select this check box, you can use NGINX built-in variables in the destination URL. Sample configurations: Path to Be Rewritten: ^/test.jpg$ Target Path: /test.${arg_type} After you enable NGINX variable calculation, the value of ${nginx_var} is calculated. ${arg_type} indicates the value of the type parameter in the original URL. Note To configure this parameter, submit a ticket.

7. Click OK.

   After a rewrite rule is created, the rule is displayed on the Access URL Rewrite tab. You can modify or delete the rule.

Sample configurations

The value of Path to Be Rewritten is a regular expression ^/hello$, which is an expression used to match a specific string pattern. The following list describes the regular expression:

• ^: matches a string from the beginning of the string.

• /hello: matches the string "/hello".

• $: matches a string to the end of the string.

This regular expression matches only the string "/hello". Examples:

• "/hello" can be matched.

• "/hello/" cannot be matched because the string contains an extra character "/" at the end.

• "hello" cannot be matched because "/" is missing from the beginning of the string.

• "/hello world" cannot be matched because the string contains extra characters after "/hello".

When a client requests http://example.aliyundoc.com/hello, which contains the string /hello, the POP writes a new URL http://example.aliyundoc.com/index.html to the Location header and returns the Location header together with an HTTP 302 status code to the client. The client initiates a request to http://example.aliyundoc.com/index.html.