HTTP access logs help you monitor information such as the persons who access the product, how many hits are received, what the errors are, etc. This information is useful for troubleshooting errors.

All WSO2 products can enable access logs for the HTTP servlet transport. This servlet transport works on 9443/9763 ports, and it receives admin/operation requests. Therefore, access logs for the servert transport is useful for analysing operational/admin-level access details. Additionally, in products such as WSO2 Enterprise Service Bus, WSO2 Enterprise Integrator (and WSO2 API Manager), access logs can be generated for the PassThrough and NIO transports. The PassThrough/NIO transports works on 8280/8243 ports and is used for API/Service invocations. By default, the access logs from both the servlet transport and the PassThrough/NIO transports are written to a common access log file located in the <EI_HOME>/repository/logs/ directory.

See the topics given below to configure the default behaviour of HTTP access logs in the ESB.

Configuring access logs for the HTTP servlet transport

Note that access logs for the HTTP servlet transport logs details of the request as well as the response on a single log line.

As the runtime of WSO2 products is based on Apache Tomcat, you can use the Access_Log_Valve variable in Tomcat as explained below to configure access logs for the HTTP servlet transport:

Open the <EI_HOME>/conf/tomcat/catalina-server.xml file (which is the server descriptor file for the embedded Tomcat integration)

Customize the attributes for the Access_Log_Valve variable shown below.

<Valve className="org.apache.catalina.valves.AccessLogValve" 
               directory="${carbon.home}/repository/logs"
               prefix="http_access_management_console_" 
               suffix=".log"
               pattern="combined" />

The attributes that are used by default are explained below. See the descriptions of the Tomcat-supported Access Log Valve attributes and customize the required values.

directory	The path to the directory that will store the access log file. By default, this location is set to "`${carbon.home}/repository/logs"` in all WSO2 products.
prefix	The prefix added to the log file's name. By default, this is "http_access_management_console_".
suffix	The suffix added to the log file's name. By default, this is ".log".
pattern	The attribute defines the format for the log pattern, which consists of the information fields from the requests and responses that should be logged. The pattern format is created using the following attributes: A standard value to represent a particular string. For example, "%h" represents the remote host name in the request. See the list of string replacement values supported by the Tomcat valve. %{xxx}i is used to represent the header in the incoming request (xxx=header value). %{xxx}o is used to represents the header in the outgoing request (xxx=header value). While you can use the above attributes to define a custom pattern, the standard patterns shown below can be used. common (Apache common log pattern): pattern=%h %l %u %t "%r" %s %b combined (Apache combined log pattern): pattern=%h %l %u %t "%r" %s %b "%{Referer}i" "%{User-Agent}i" Note that, by default, the "combined" pattern is enabled in the ESB.

Restart the server. According to the default configurations, a log file named http_access_management_console_.{DATE}.log is created inside the <EI_HOME>/repository/logs directory. The log is rotated on a daily basis.

Configuring access logs for the PassThrough and NIO transports (Service/API invocation)

Note that access logs for the PassThrough/NIO transports log the request and the response on two separate log lines.

By default, access logs related to service/API invocation are disabled for performance reasons in the above products. You should enable these access log only for troubleshooting errors. Follow the steps given below to enable access logs for the PassThrough transport:

Change the log level from WARN to INFO for the following entry in the <EI_HOME>/conf/log4j.properties configuration file.
```
log4j.logger.org.apache.synapse.transport.http.access=INFO
```

You can customize the format of this access log by changing the following property values in the <EI_HOME>/conf/access-log.properties configuration file. If this file does not exist in the product by default, you can create a new file with the following parameters.

access_log_directory	Add this property ONLY if you want to change the default location of the log file. By default, the product is configured to store access logs in the `<EI_HOME>/repository/logs` directory.
access_log_prefix	The prefix added to the log file's name. The default value is as follows: access_log_prefix=http_access_
access_log_suffix	The suffix added to the log file's name. The default value is as follows: access_log_suffix=.log
access_log_file_date_format	The date format used in access logs. The default value is as follows: access_log_file_date_format=yyyy-MM-dd
access_log_pattern	The attribute defines the format for the log pattern, which consists of the information fields from the requests and responses that should be logged. The pattern format is created using the following attributes: A standard value to represent a particular string. For example, "%h" represents the remote host name in the request. Note that all the string replacement values supported by Tomcat are NOT supported for the PassThrough transport's access logs. The list of supported values are given below. %{xxx}i is used to represent the header in the incoming request (xxx=header value). %{xxx}o is used to represents the header in the outgoing request (xxx=header value). While you can use the above attributes to define a custom pattern, the standard patterns shown below can be used. common (Apache common log pattern): access_log_pattern=%h %l %u %t "%r" %s %b combined (Apache combined log pattern): access_log_pattern=%h %l %u %t "%r" %s %b "%{Referer}i" "%{User-Agent}i" By default, a modified version of the Apache combined log format is enabled in the ESB as shown below. Note that the "X-Forwarded-For" header is appended to the beginning of the usually combined log format. This correctly identifies the original node that sent the request (in situations where requests go through a proxy such as a load balancer). The "X-Forwarded-For" header must be present in the incoming request for this to be logged. access_log_pattern=%{X-Forwarded-For}i %h %l %u %t \"%r\" %s %b \"%{Referer}i\" \"%{User-Agent}i\"

Restart the server.
Invoke a proxy service or REST API that is deployed in the ESB. For testing purposes, use the artifacts in the quick start guide.
The access log file for the service/API will be created in the <EI_HOME>/repository/logs directory. The default name of the log file is http_access_.log.

Note that there will be delay in printing the logs to the log file.

Supported log pattern formats for the PassThrough and NIO transports

Although the WSO2 logging implementation is based on the Tomcat implementation, the set of attributes supported by the WSO2 logging implementation is different from the string replacement values supported by Tomcat.

Attribute	Description
`%a`	Remote IP address
`%A`	Local IP address
`%b`	Bytes sent, excluding HTTP headers, or '-' if zero
`%B`	Bytes sent, excluding HTTP headers
`%c`	Cookie value
`%C`	Accept header
`%e`	Accept Encoding
`%E`	Transfer Encoding
`%h`	Remote host name (or IP address if enableLookups for the connector is false)
`%l`	Remote logical username from identd (always returns '-')
`%L`	Accept Language
`%k`	Keep Alive
`%m`	Request method (GET, POST, etc.)
`%n`	Content Encoding
`%r`	Request Element
`%s`	HTTP status code of the response
`%S`	Accept Chatset
`%t`	Date and time, in Common Log Format
`%T`	Content type
`%u`	Remote user that was authenticated (if any), else '-'
`%U`	Requested URL path
`%v`	Local server name
`%V`	Vary Header
`%x`	Connection Header
`%Z`	Server Header