502 Gateway Errors back again


Hi ,
A while back we were getting 502 errors from Nginx. I upped some values for PHP and Nginx after moving to a new AWS Virtual server with 30 GB RAM and 4 CPUs. But we started seeing a few again just navigating the Mailwizz pages. Also we got reports from our subscribers, recipients of emails, that they got them at times also. Today we were sending 6 campaigns set an hour apart for about 300,000 emails total. I took a look at the Nginx error log and was surprised to see about 8 errors every second! They were almost all like:

2017/11/28 14:36:47 [error] 9719#9719: *3351082 connect() to unix:/run/php/php7.0-fpm.sock failed (11: Resource temporarily unavailable) while connecting to upstream, client:, server: email.causeaction.com, request: "POST /index.php/dswh/9 HTTP/1.1", upstream: "fastcgi://unix:/run/php/php7.0-fpm.sock:", host: "mailer.causeaction.com"

I am a Linux newbie. Just stared learning Linux 6 months ago when we started using Mailwizz.
I'm wondering if ALL these errors return 502 errors....for example upon Link Click or Unsubscribe. That would make for a lot of unhappy subscribers. Or are some of these actually retried until they succeed? For example, such that the subscriber might see a several-second delay before the process actually completes?

Thanks for any enlightenment on this subject. I have uploaded a partial copy of the Nginx error.log file


  • error_copy.txt
    27.4 KB · Views: 6
OK Thanks Twisted. I read several articles today and tried changing some configurations to see if it would help. I will read these articles completely and see what I may have missed.