Advanced Forwarding
Overview
Advanced forwarding policies are available only for dedicated load balancers. If you have enabled Advanced Forwarding, you can add advanced forwarding policies to HTTP and HTTPS listeners of dedicated load balancers.
You can add advanced forwarding policies to HTTP or HTTPS listeners to forward requests to different backend server groups based on HTTP request method, HTTP header, query string, or CIDR block in addition to domain names and URLs. Table 1 describes the rules and actions that you can configure for request forwarding.
The following describes how an advanced forwarding policy works:
- The client sends a request to the load balancer.
- The load balancer matches the request based on the forwarding rule you configure.
- The load balancer forwards the request to the corresponding backend server or returns a fixed response to the client based on the action you configure.
- The load balancer sends a response to the client.
Forwarding Policy |
Description |
---|---|
Forwarding rule |
There are six types of forwarding rules: domain name, URL, HTTP request method, HTTP header, query string, and CIDR block For details, see Forwarding Rule. |
Action |
The following actions are supported: forward to a backend server group, redirect to another listener, redirect to another URL, and return a specific response body. For details, see Action Types. |
How Requests Are Matched
After you add an HTTP or HTTPS listener to a load balancer, a default forwarding policy is generated. This policy uses the protocol and port specified for the listener to match requests and forward the requests to the backend server group you specified when adding the listener.
The default forwarding policy has the lowest priority and is not included when you sort forwarding policies. It can be edited but cannot be deleted.
Each request is matched based on the forwarding policy priority (a smaller value indicates a higher priority). Once a forwarding policy is matched, the request is forwarded based on this forwarding policy.
- If the request is matched with any forwarding policy of the listener, it is forwarded based on this forwarding policy.
- If the request is not matched with any forwarding policy, it is forwarded based on the default forwarding policy.
Forwarding Rule
Advanced forwarding policies support the following types of forwarding rules: domain name, URL, HTTP request method, HTTP header, query string, and CIDR block (source IP addresses).
Forwarding Rule |
Description |
---|---|
Domain name |
Example Request URL: https://www.example.com/login.php?locale=en-us=#videos Domain name in the forwarding rule: www.example.com |
URL |
For more information about URL matching rules, see URL Matching. Example Request URL: https://www.example.com/login.php?locale=en-us#videos URL in the forwarding rule: /login.php |
Query string |
Route requests based on the query string.
A query string consists of a key and one or more values. You need to set the key and values separately.
Example Request URL: https://www.example.com/login.php?locale=en-us#videos A query string needs to be configured for the forwarding rule: Key: locale Value: en-us |
HTTP request method |
Route requests based on the HTTP method.
Example GET |
HTTP header |
Route requests based on the HTTP header.
An HTTP header consists of a key and one or more values. You need to configure the key and values separately.
Example Key: Accept-Language Value: en-us |
CIDR block |
Route requests based on the source IP addresses from where requests originate. Example 192.168.1.0/24 or 2020:50::44/127 |
Action Types
Advanced forwarding policies support the following actions: forward to a backend server group, redirect to another listener, redirect to another URL, and return a specific response body.
Action |
Description |
---|---|
Forward to a backend server group |
Requests are forwarded to the specified backend server group. |
Redirect to another listener |
Requests are redirected to another listener, which then routes the requests to its associated backend server group.
NOTE:
If you select Redirect to another listener and create a redirect for the listener, it will redirect the requests to the specified HTTPS listener, but access control configured for the listener will still take effect. For example, if you configure a redirect for an HTTP listener, HTTP requests to access a web page will be redirected to the HTTPS listener you select and handled by the backend servers associated with the HTTPS listener. As a result, the clients access the web page over HTTPS. The configuration of the HTTP listener will become invalid. |
Redirect to another URL |
Requests are redirected to the configured URL. When clients access website A, the load balancer returns 302 or any other 3xx status code and automatically redirects the clients to website B. You can custom the redirection URL that will be returned to the clients.
Configure at least one of the following components:
Example URL for redirection: http://www.example1.com/index.html?locale=en-us#videos Protocol: HTTP Domain name: www.example1.com Port: 8081 Path: /index.html Query String: locale=en-us HTTP Status Code: 301 |
Return a specific response body |
Load balancers return a fixed response to the clients. You can custom the status code and response body that load balancers directly return to the clients without the need to route the requests to backend servers.
Configure the following components:
Example text/plain Sorry, the language is not supported. text/css <head><style type="text/css">div {background-color:red}#div {font-size:15px;color:red}</style></head> text/html <form action="/" method="post" enctype="multipart/form-data"><input type="text" name="description" value="some text"><input type="file" name="myFile"><button type="submit">Submit</button></form> application/javascript String.prototype.trim = function() {var reExtraSpace = /^\s*(.*?)\s+$/;return this.replace(reExtraSpace, "$1")} application/json { "publicip": { "type": "5_bgp","ip_version": 4},"bandwidth": {"name": "bandwidth123","size": 10,"share_type": "PER"}}
NOTE:
Ensure that the response body does not contain carriage return characters. Otherwise, it cannot be saved. |
URL Matching
Table 4 shows how URLs configured in the forwarding policies match the URLs in the requests.
Request URL |
Forwarding Policy |
URL in the Forwarding Policy |
Matching Mode |
Forwarding Policy Priority |
Destination Backend Server Group |
---|---|---|---|---|---|
/elb/abc.html |
Forwarding policy 01 |
/elb/abc.html |
Prefix match |
1 |
Backend server group 01 |
Forwarding policy 02 |
/elb |
Prefix match |
2 |
Backend server group 02 |
|
/exa/index.html |
Forwarding policy 03 |
/exa[^\s]* |
Regular expression match |
3 |
Backend server group 03 |
Forwarding policy 04 |
/exa/index.html |
Regular expression match |
4 |
Backend server group 04 |
|
/mpl/index.html |
Forwarding policy 05 |
/mpl/index.html |
Exact match |
5 |
Backend server group 05 |
URLs are matched as follows:
- When the request URL is /elb/abc.html, it matches both forwarding policy 01 and forwarding policy 02. However, the priority of forwarding policy 01 is higher than that of forwarding policy 02. Forwarding policy 01 is used, and requests are forwarded to backend server group 01.
- When the request URL is /exa/index.html, it matches both forwarding policy 03 and forwarding policy 04. However, the priority of forwarding policy 03 is higher than that of forwarding policy 04. Forwarding policy 03 is used, and requests are forwarded to backend server group 03.
- If the request URL is /mpl/index.html, it matches forwarding policy 05 exactly, and requests are forwarded to backend server group 05.
URL Matching Based on Regular Expressions
A path can contain letters, digits, and special characters _~';@^-%#&$.*+?,=!:|\/()[]{} and must start with a slash (/). ${path} retains the path of the request.
If you select regular expression match, the request path will be overwritten by the variables that match the regular expressions.
How Request Paths Are Overwritten
- URL matching: The client sends a request, and the request matches a regular expression in the forwarding rule. You can specify one or more regular expressions as the match conditions and set multiple capture groups represented by parentheses ( ) for one regular expression.
- Extraction and replacement: extracts the content from the capture groups.
- Destination path: writes them to $1, $2, all the way to $9 configured for the path.
Example
When a client requests to access /test/ELB/elb/index, which matches the regular expression /test/(.*)/(.*)/index, $1 will be replaced by ELB and $2 by elb, and then the request will be redirected to /ELB/elb.
Matching Step |
Description |
||
---|---|---|---|
Forwarding rule: URL |
Regular expression match |
|
|
Action: redirect to another URL |
Path |
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