Logs and Monitoring for Apache Servers | Page 2

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Logs and Monitoring for Apache Servers

Creating a Custom Log File

You may want to create new log files in addition to the ones included with Apache. This example uses CustomLog to create a new log file and store the information defined by a previously defined log format named common, as seen in the previous section. You can replace the nickname with the format definition itself. An additional, simpler directive is Transferlog, which will just take the definition provided by the latest LogFormat directive.

Redirecting Logs to an External Program

You can also use CustomLog or TransferLog to redirect ("pipe") the log output to an external program instead of a file. To do this, you need to begin with the pipe character "|", followed by the path to a program that will receive the log information on its standard input. This example uses the rotatelogs program included with Apache, which is described in a later section.

When an external program is used, it will be run as the user who started httpd. This will be root if the server was started by root; be absolutely sure that the program is secure. Also, when entering a file path on non-Unix platforms, care should be taken to make sure that only forward slashes are used, even though the platform may allow the use of backslashes. In general, it is a good idea to always use forward slashes throughout the configuration files.

Logging Requests Conditionally

You can decide whether or not to log a request based on the presence of an environment variable. This variable can be previously set based on a number of parameters, such as the client's IP address or the presence of a certain header in the request. As shown in this example, the CustomLog directive can accept an environment variable as a third argument. If the environment variable is present, the entry will be logged; otherwise, it will not. If the environment variable is negated by prefixing it with an "!", the entry will be logged if the variable is /not/ present. The example shows you how to avoid logging images in GIF and JPEG format and how to log requests from a particular IP address to a separate log file. See the next section for another example.

Monitoring Who Is Linking to Your Website

In order to monitor who is linking to your website, you can log the Referer: header from the request. This header contains the URL that linked to the page being requested. While not always present or accurate, it works for the majority of cases. This example shows how to use an environment variable to log the referrer information to a separate file. In this particular case, we are only interested in logging external referers, not those that come from an internal web page. To do so, in this example we check whether the referrer matches our own domain.

Monitoring Apache with mod_status

The mod_status module provides information on server activity and performance, allowing a server administrator to find out how well their server is performing. An HTML page is presented that gives the current server statistics in an easily readable form, such as the number of workers serving requests, the number of idle workers, the time the server was started/restarted, and so on.

If you include an ExtendedStatus On directive, additional information will be displayed, such as individual information about each worker status, total number of accesses, current requests being processed, and so on.

Bear in mind that, depending on your server load, this extended statistics recording may have a significant impact on server performance.

This example shows how to enable the mod_status monitoring, while restricting access to this information to only certain IP addresses. You can now access server statistics by using a Web browser to access the page at https://www.example.com/server-status.

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