Request mapping: WebSphere Proxy Server

The proxy server uses request mapping to match an HTTP request that is received to an application that is deployed in the cell or routing rule.

Unlike the Apache Web Server or Caching Proxy, which have flat configuration files with routing precedence that is inherent to the ordering of directives, the proxy server uses a best match mechanism to determine the installed application or routing rule that corresponds to a request. The virtual host or URI patterns determine the best match for a web module or routing rule. For applications that are deployed in clusters, the proxy server maintains affinity (Secure Sockets Layer ID, cookie, and URL rewriting), otherwise, a weighted round-robin approach is used to select the target server. The following examples address various routing scenarios for when routing rules and applications are deployed within the same cell.

Proxy environment

A WebSphere proxy server called proxy1 is active in the same cell as the applications and routing rules. All of the applications and routing rules are enabled in the cell for proxy1, and PROXY_HTTP_ADDRESS for proxy1 is set to 80.

Virtual host	Host name	Port
default_host	host1.company.com	80
	host1.company.com	9080
	*	80
proxy_host	host2.company.com	80
	*	443
	*	80
server_host	host3.company.com	80

URI group name	URI patterns
ALL	/*
ROOMS	/kitchen/*, /bathroom/*, /bedroom/*
CONFLICT	/WM2C/*

Generic server cluster name	Protocol	Host	Port
CLUSTER1	HTTP	webserver1.company.com	9081
		webserver2.company.com	9083
CLUSTER2	HTTP	host47.company.com	8088
		host48.company.com	8088
CLUSTER2-SSL	HTTPS	host47.company.com	8443
		host48.company.com	8443

Routing rule name	Virtual host	URI group	Action
ALLTOCLUSTER1	proxy_host	ALL	Generic server cluster - CLUSTER1
ROOMTOCLUSTER2	proxy_host	ROOMS	Generic server cluster - CLUSTER2
ALLTOCLUSTER2	server_host	ALL	Generic server cluster - CLUSTER2
REDIRECTTOCONFLICT	default_host	CONFLICT	Redirect - http://www.conflict.com

Application name	Context root	Web module name	Virtual host	Web module URI patterns
App1	/WM1A/	Web Mod A	default_host	wm1a.jsp
	/WM1B/	Web Mod B	default_host	wm1b.jsp
App2	/WM2C/	Web Mod C	default_host	/*, wm2c.jsp
	/WM2D/	Web Mod D	default_host	/*, wm2d.jsp

Example 1: Basic request

The proxy1 proxy receives the following request:

GET /WM1A/wm1a.jsp HTTP/1.1 
Host: host1.company.com

The result is the wm1a.jsp file is sent as the response. The ALLTOCLUSTER1 routing rule is a possible match, but Web Mod A is chosen as the best match by proxy1 because the combination of its context root and URI pattern /WM1A/wm1a.jsp is a better match than /*. Web Mod A is also chosen as the best match because its virtual host contains the host1.company.com:80 alias, which is a more specific match than the *:80 wild card alias.

Example 2: Routing rules that use the same URI group and different virtual hosts

The proxy1 proxy receives the following request:

GET /index.html HTTP/1.1 
Host: host3.company.com

The result is the proxy1 proxy maps the request to the ALLTOCLUSTER2 routing rule, and a response is received from a server in CLUSTER2. The ALLTOCLUSTER1 routing rule is a possible match and can handle the request if the ALLTOCLUSTER2 routing rule did not exist. However, the ALLTOCLUSTER2 rule is the best match because its virtual host (server_host) explicitly lists host3.company.com.

Example 3: Routing rules that use same virtual host and different URI groups

The proxy1 proxy receives the following request:

GET /kitchen/sink.gif HTTP/1.1 
Host: host2.company.com

The result is the proxy1 proxy maps the request to the ROOMSTOCLUSTER2 routing rule and a server from the CLUSTER2 cluster sends a response. The ALLTOCLUSTER1 routing rule is a possible match, but the ROOMSTOCLUSTER2 rule is the best match because its URI group contains a pattern /kitchen/* that is a better match for the request URI /kitchen/sink.gif.

Example 4: Routing rule URI group conflicts with URI pattern of a web module that uses the same virtual host

The proxy1 proxy receives the following request:

GET /WM2C/index.html HTTP/1.1 
Host: host1.company.com

The result is indeterminate. It is unknown whether Web Mod C or the REDIRECTTOCONFLICT routing rule handles the request because they use the same virtual host and have the same URI pattern. In such cases, the ID DWCT0007E message is displayed in SystemOut.log file for the proxy1 proxy. In this example, changing the REDIRECTTOCONFLICT routing rule to use a different virtual host resolves the problem.

IBM recommends using the High Performance Extensible Logging (HPEL) log and trace infrastructure . We view HPEL log and trace information using the logViewer .

Example 5: The PROXY_HTTP_ADDRESS address is not in the virtual host

Assume that the proxy1 proxy address, PROXY_HTTP_ADDRESS, is changed to 81, while all of the other configuration information remains the same. The proxy1 proxy receives the following request:

GET /index.html HTTP/1.1 
Host: host1.company.com:81

The result is the proxy1 proxy is unable to handle the request because the PROXY_HTTP_ADDRESS address is not available in a virtual host and will send an HTTP 404 response back to the client.

Use High Performance Extensible Logging to troubleshoot applications