====== Apache - Troubleshooting - Debugging requests and responses ======

There are times when a problem can be caused by an application server, proxy server or the web server itself.

To dump HTTP requests and responses, the **mod_dumpio** Apache web server module can be used.

  * Tt allows HTTP requests and/or HTTP responses to be written to the **error_log**.

Setting up **mod_dumpio** is simple and straight forward.

  * To dump HTTP requests to the error_log, the **DumpIOInput** directive can be set to **On**.
  * To dump HTTP responses to the error_log, the **DumpIOOutput** directive can be set to **On**.

Once these directives are enabled, entries similar to the following will be written to the error_log each time a request is received, or a response is sent:

<code bash>
[Mon Oct 12 12:13:14 2016] [debug] mod_dumpio.c(103): mod_dumpio: dumpio_in [getline-blocking] 0 readbytes
[Mon Oct 12 12:13:14 2016] [debug] mod_dumpio.c(51): mod_dumpio:  dumpio_in (data-HEAP): 16 bytes
[Mon Oct 12 12:13:14 2016] [debug] mod_dumpio.c(67): mod_dumpio:  dumpio_in (data-HEAP): GET / HTTP/1.1rn
</code>

<WRAP info>
**NOTE:**  **mod_dumpio** adds some additional overhead to request processing, and the configuration directives will require a server restart.

A graceful restart can be used to avoid killing active connections.
</WRAP>