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nginx: trigger slow php-fpm process, but quickly return status 200

Is it possible for nginx to trigger a php-fpm process, but then close the nginx worker and quickly return an empty page with status 200?

I have some slow php processes that need kicking off a few times a week. They can take between 3 and 4 minutes each. I trigger them with a cron manager site. The php process writes a lock file at the start, and when the process is complete an email is sent and finally the lock file is removed.

Following this guide, in my php-fpm worker pool, I have this: request_terminate_timeout = 300 and in my nginx site config I have fastcgi_read_timeout 300;

It works, but I don't care about the on-screen result. And the cron service I use has a time limit of 5 seconds, and after repeated timeouts, it disables the job.

Yes, I know I could fork a process in php, let it run in the background, and return a 200 to nginx. And yes, I could pay and upgrade my cron service. Nonetheless, it would be an interesting and useful thing to know, anyway.

So, is this possible, or does php-fpm require an open and "live" socket? I ask that because on the "increase your timeout" page referred to above, one answer says

"Lowest of three. It’s line chain. Nginx->PHP-FPM->PHP. Whoever dies first will break the chain".

In other words, does that mean that I can never "trigger" a process, but then close the nginx part of the trigger?

Solution

  • You can.

    1. exec a php cli script by adding a trailing &, redirecting output to a log file or /dev/null, pass any parameters as json or serialized (use escapeshellarg()), the exec will return 0 immediately (no error); or
    2. use php's ignore_user_abort(), send a Connection: close header, flush any output buffers as well as a normal flush(). Put any slow code after that. You'll need to test this under Nginx.

    Either way, return a 202 code to signify acceptance but no response. And it's up you to make sure your script doesn't run forever; give it a heartbeat so it touch()es a file every so often. If the file is old and it's still running, kill it.