HTTP Access Logging

HTTP Requests/Responses are logged in the access log(s) and are helpful to monitor your application's usage activities, such as the persons who access it, how many hits it receives, what the errors are etc. This information is useful for troubleshooting. As the runtime of WSO2 products are based on Apache Tomcat, you can use the Access_Log_Valve variable in Tomcat 7 as explained below to configure HTTP access logs in WSO2 products. In addition, you can customize the access logs based on the supported Access Log Valve attributes. 

Configuring HTTP access logging

To configure HTTP access logs:

1. Edit the Access_Log_Valve variable as follows in the <PRODUCT_HOME>/repository/conf/tomcat/catalina-server.xml file, which is the server descriptor file for the embedded Tomcat integration.

   <Valve className="org.apache.catalina.valves.AccessLogValve"
   directory="${carbon.home}/repository/logs"
   prefix="localhost_access_log_sample."
   suffix=".log"
   pattern="%{xxx}i %{xxx}o"
   resolveHosts="false"/>

   The pattern attribute defines the formatting layout, which consists of the information fields from the requests and responses that should be logged. The description of the formatting layout specified in the above pattern attribute is given below. For more example configurations, see Customizing access logs by pattern.

   • xxx - header name we need to log
   • %{xxx}i - incoming request headers
   • %{xxx}o - outgoing response headers

   For more information on all possible values that can be given in the pattern parameter, go to:
   http://tomcat.apache.org/tomcat-7.0-doc/config/valve.html#Access_Log_Valve

   If you do not wish to customize the formatting layout, you can simply use the word 'common' or 'combined' for the pattern attribute to select a standard format. 

   • common - %h %l %u %t "%r" %s %b

   • combined - %h %l %u %t "%r" %s %b "%{Referer}i" "%{User-Agent}i"

     The optimized access only supports 'common' and 'combined' as the value for this attribute.

2. Restart the server. This will create a log file named  localhost_access_log_sample.{DATE}.log  inside the <PRODUCT_HOME>/repository/logs  directory.

Customizing access logs by pattern

Given below are a few sample configurations, for ways in which the access logs can be customized by the pattern attribute:

Example 1: Logging request headers

The configuration is as follows:

<Valve className="org.apache.catalina.valves.AccessLogValve"
directory="${carbon.home}/repository/logs"
prefix="localhost_access_log_test."
suffix=".log"
pattern="%{Content-Type}i %{Accept}i %{Accept-Encoding}i"
resolveHosts="false"/>

This sample configuration logs the Content-type, Accept and Accept-encoding headers of every request coming to the server. For example, in the following example, we use the RequestInfoExample to send the HTTP request:

GET http://<IP>:<PORT>/example/servlets/servlet/RequestInfoExample?abc=xyz

It records the following log entry in the  localhost_access_log_sample.{DATE}.log  file.

text/plain; charset=utf-8        */*        gzip,deflate,sdch

Example 2: Logging response headers

The configuration is as follows:

<Valve className="org.apache.catalina.valves.AccessLogValve"
directory="${carbon.home}/repository/logs"
prefix="localhost_access_log_test."
suffix=".log"
pattern="%{Content-Type}o %{Content-Length}o %{Date}o %{Server}o"
resolveHosts="false"/>

The above configuration sample logs the Content-type, Content-Length, Date and Server headers of every response coming from the server as follows:

text/html;charset=ISO-8859-1       662       Tue, 09 Jul 2013 11:21:50 GMT        WSO2 Carbon

Example 3: Logging other variable values

The configuration is as follows:

<Valve className="org.apache.catalina.valves.AccessLogValve"
directory="${carbon.home}/repository/logs"
prefix="localhost_access_log_test."
suffix=".log"
pattern="%r %q %h"
resolveHosts="false"/>

The above sample configuration logs the first line of the request (method and request URI), query string (prepended with a '?' if it exists) and remote hostname (or IP) of every request coming to the server as follows. 

“GET /example/servlets/servlet/RequestInfoExample?abc=xyz HTTP/1.1”      ?abc=xyz     10.100.0.67

Example 4: Logging URL encoded parameters

You cannot use the AccessLogValve to log URL encoded parameters. However, you can use the ExtendedAccessLogValve attribute for this purpose. In this example only two values (namely, className and pattern) are modified from the previous configuration.

The configuration is as follows:

<Valve className="org.apache.catalina.valves.ExtendedAccessLogValve" 
directory="${carbon.home}/repository/logs"
prefix="localhost_access_log_extended."
suffix=".log"
pattern="x-P(param1) x-P(param2)"
resolveHosts="false"/>

Send the POST request together with the URL encoded values such as  param1=value1 and param2=value2 as follows:

POST http://<IP>:<PORT>/example/servlets/servlet/RequestInfoExample

The above sample configuration logs the following:

'value1'     'value2'