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I'm running Drupal 6 with Nginx 1.5.1 and PHP-FPM (PHP 5.3.26) on a 1GB single core VPS with 3GB of swap space on SSD storage. I just switched from shared hosting to this unmanaged VPS because my site was getting too heavy, so I'm still learning the ropes. I have moderately high traffic, I don't really monitor it closely but Google Adsense usually record close to 30K page views/day. I usually have 50 to 80 authenticated users logged in and a few hundred more anonymous users hitting the Boost static HTML cache at any given moment. I have a maximum of 10 PHP-FPM child processes configured. I am using the "ondemand" PHP-FPM process manager.

I'm running into an occasional error that is really hard to debug because it's seemingly random. Out of maybe 30 intentional posts by users, 1 of them gets duplicated. I configured it so the post button is disabled after the first click, so it's not the result of double clicking. In fact, it even happened to me once when I was posting. The double posts occur within a few seconds of each other. I examined the log files, and the duplicate post always seems to correspond to an nginx POST error: recv() failed (104: Connection reset by peer) while reading response header from upstream. And this event seems to relate to a PHP-FPM error of an execution timeout error of index.php and subsequent SIGTERM of the PHP-FPM worker process.

Here are links to the nginx access and error logs and the PHP-FPM error log.

They are pruned and slightly obfuscated to show a duplicate post error that just happened today at 12:34 by me with an IP address of "". The node on which the dupe happened is 22802.

This issue did not occur when I was running on Apache/FastCGI on my previous shared webhost. I should also mention that I am using Redis for caching and the Zend Optimizer+ opcache. But I tried disabling both of those mechanisms to avoid the dupes error, and it made no difference.

Thanks for any help you can provide!

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Why aren't you on Drupal 7 already? – Michael Hampton Jul 2 '13 at 18:10
I'm still dependant on some Drupal 6 modules. Drupal 6/7 isn't the issue here, though. – rahim123 Jul 2 '13 at 18:18
As for the Drupal 6/7 thing, I never had problems with double posting on Drupal 6 on my previous host. It's some sort of config issue with PHP-FPM I suspect. – rahim123 Jul 2 '13 at 18:24

Well, I'm going to answer my own question. The problem apparently had something to do with the request_terminate_timeout = 30s value that I was using, possibly combined with the ondemand FPM process manager. The double post always coincided with a PHP-FPM timeout error combined with a killing of a child process immediately after. So I disabled the request_terminate_timeout, and it appears to be redundant anyway since the php.ini file already specifies a 30 second timeout. I also realized that I don't really need the ondemand process manager because I'm the only user on this box with fairly stable load, so I switched to static and set the pm.max_requests fairly low to 100. This prevents memory leaks.

One or both of these changes has effectively eliminated the duplicates posts.

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