# 499 errors in IE9 causing order duplicates **URL:** \ **Category:** NGINX\ **Created:** [October 26, 2010, 3:49pm UTC](https://www.ruby-forum.com/t/499-errors-in-ie9-causing-order-duplicates/198113 "2010-10-26T15:49:42Z")\ **Posts on this page:** 2\ **Page:** 1
**Author:** ![Dobai-Pataky\_BSSSSl](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/77aa72/32.png) [@Dobai-Pataky\_BSSSSl](https://www.ruby-forum.com/u/Dobai-Pataky_BSSSSl)\ **Post date:** [October 26, 2010, 3:49pm UTC](https://www.ruby-forum.com/t/499-errors-in-ie9-causing-order-duplicates/198113/1 "2010-10-26T15:49:42Z")
We use nginx to reverse proxy to a farm of apache servers. It rocks. But we’ve noticed that Internet Explorer 9 has been generating duplicate orders. It does not happen every time, but often enough. It appears to be an IE 9 issue, but I’m hoping the experts here can confirm my theory: A request comes from an IE 9 client. Nginx passes the request to an upstream apache server. For some reason, the IE 9 browser closes the connection before the apache server returns results with return code 200. Nginx sees a closed connection, and generates a 499 error (client problem, connection closed). IE 9 sees that, and immediately re-sends the request. Nginx forwards to apache, receives the response, and forward to the client, logging a 200. Log results are below Does this seem correct? Anyone else seeing this behavior? Any suggestions for a graceful way to handle this? (Duplicate orders BAD) Thanks, ``` -Paleo ``` On nginx, we see: XX.XX.XX.XX - - [14/Oct/2010:18:01:31 -0400] “POST /checkout.php HTTP/1.1” 499 0 “[https://www.somesite.com/precheckout.php](https://www.somesite.com/precheckout.php)” “Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; Trident/5.0)” “-” XX.XX.XX.XX - - [14/Oct/2010:18:01:33 -0400] “POST /checkout.php HTTP/1.1” 200 6996 “[https://www.somesite.com/precheckout.php](https://www.somesite.com/precheckout.php)” “Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; Trident/5.0)” “-” And on apache, the same requests log: XX.XX.XX.XX - - [14/Oct/2010:18:01:30 -0400] “POST /checkout.php HTTP/1.0” 200 6996 “[https://www.somesite.com/precheckout.php](https://www.somesite.com/precheckout.php)” “Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; Trident/5.0)” google XX.XX.XX.XX - - [14/Oct/2010:18:01:30 -0400] “POST /checkout.php HTTP/1.0” 200 6996 “[https://www.somesite.com/precheckout.php](https://www.somesite.com/precheckout.php)” “Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; Trident/5.0)” google ---
**Author:** ![Paleo\_Tek](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/ce73a5/32.png) [@Paleo\_Tek](https://www.ruby-forum.com/u/Paleo_Tek)\ **Post date:** [October 26, 2010, 8:43pm UTC](https://www.ruby-forum.com/t/499-errors-in-ie9-causing-order-duplicates/198113/2 "2010-10-26T20:43:04Z")
Hello! On Tue, Oct 26, 2010 at 09:48:23AM -0400, Paleo Tek wrote: > (client problem, connection closed). IE 9 sees that, and > immediately re-sends the request. Nginx forwards to apache, > receives the response, and forward to the client, logging a 200. > Log results are below IE can’t “see” 499 as it’s logged after client already closed connection. It’s IE who closed connection (which is logged with 499 fake code) and re-issued request. Most likely reason - user hit “Submit” button two times (so on second click IE aborted first request and issued another one). This problems isn’t nginx and/or IE specific, though may show in logs slightly differently depending on exact borwser and/or server behaviour. Usual methods to prevent it from happening - either use javascript to disable submit button, or use some token in form and filter duplicates at server side, see e.g. [1]. [1] [http://stackoverflow.com/questions/414835/avoid-race-conditions-in-php-on-submit-please-do-not-click-submit-more-than-once](http://stackoverflow.com/questions/414835/avoid-race-conditions-in-php-on-submit-please-do-not-click-submit-more-than-once) Maxim D.