Error code 503: "Service Unavailable" - AFS

AFS Integration Guide

Reference Guide

"The server is currently unable to handle the request due to a temporary overloading or maintenance of the server. The implication is that this is a temporary condition which will be alleviated after some delay." (source)

  • This error occurs when there are too many queries waiting to be processed by the Query Manager. If the processing queue becomes too large then HTTP 503 error codes are issued to new clients until the load becomes small enough to ensure nominal processing.

Code integrating AFS should try to repost queries when obtaining a 503 error code. The new posts should delayed by a reasonable amount of time and limited to a few retries.


  • Query at t0, get error code 503
  • Post query again at t0+1s, get error code 503
  • Post query again at t0+2s, get a reply

  • This error code can also appear when any error happens between the (Fast)CGI and the Query Manager. This error should be logged in the web server error log, with a message like "Error! ..."

  • This error occurs when Query Manager is synchronizing its reply databases with Update Manager.