I have a problem, that I can not solve. Some of the communication (~10-20%) between the frontend and the backend server has stuck. Can anyone give me an advice?

Frontend PHP --------- curl --------> Backend PHP

• The frontend sends the request and it is arriving immediately to the Apache
• In the backend log there is a 5 sec delay for the start of the operation
• The backend log says that the operation was fast

Example:

• frontend curl log:

  16:30:00.00 - Runtime: 5.2454 
  

• backend apache access log:

  16:30:00.01 - /backend/.... 
  

• backend log:

  16:30:05.01 - Runtime: 0.2254
  

The way that I am logging:

• Frontend log:

  <?php
  ....
  startTime
  send curl request to Backend IP
  write to the log: currentTime, currentTime-startTime
  ...
  ?>
  

• Backend log:

  <?php
  startTime
  PHP/MySQL/Redis/etc
  write to the log: currentTime, currentTime-startTime
  ?>
  

Server

• Debian 6.0.3
• Apache/2.2.16
• PHP 5.3.3
• MySQL Ver 14.14 Distrib 5.1.49
• Redis server 2.4.2