Apache – PHP Scripts Suddenly Load Very Slow on Apache

apache-2.4php-fpmubuntu-20.04

I am testing why sometimes my PHP scripts takes long to load over network (>30sec) on my Apache 2.4 Ubuntu server with PHP-FPM 7.4 using mpm_event. The server was working normally in the past few months, this started happening a few days ago and I didn't change anything. I did a reboot, it didn't help.

I've made a simple test.php. Sometimes it loads normally (<100ms), but sometimes it takes 1 minute to load:

<?php echo "test\n"; ?>

Server's CPU, RAM and IO are all normal (checked with htop).
Static HTML files are loaded without any delays.
Running script locally via SSH console is very fast.
Apache error logs doesn't show anything unusual.
I checked if there is some DDOS attack by checking the number of connected IPs from same /16 subnet and didn't find anything weird (e.g. >100 connections).

How can I debug this further to see why this is happening?

Some debug output which may help:

sudo service php7.4-fpm status

Best Answer

There may be several reasons for this behavior:

If this web server processes requests from the external network, then with the increase in the amount of traffic, the load could increase, which led to an increase in the server response time.
If your scripts use calls to external resources, then in this case the response time of your server may increase due to the low response speed of the external resource.

Log message:

[30-Sep-2021 03:36:46] WARNING: [pool www] server reached pm.max_children setting (5), consider raising it

is just proof of the increased load.

In both cases, you should determine the reasons for the load by analyzing the number of requests to the scripts, and if there are calls to external resources, make sure that they work correctly.

Related Solutions

Nginx – Constantly have to reload PHP-FPM

You're using php-fpm, so I suggest to be more aggressive with how long php-fpm's children are allowed to live. You need to find the sweet spot between shortly lived threads/children and stability. The php-fpm defaults are way to generous for any production system, IMHO.

I'd reduce the number for pm.max_requests for your production pools. I think the default is 200. I'd start from 50 and see where that takes you.

Failing/complementary to that, you could also try these global options (AFAIK they are all disabled by default):

emergency_restart_threshold=3
emergency_restart_interval=1m
process_control_timeout=5s

What does this mean? If 3 PHP-FPM child processes exit with SIGSEGV or SIGBUS (i.e. crash) within 1 minute then PHP-FPM is supposed to restart automatically. The child processes wait 5s for a reaction on signals from master.

This should keep your pool of PHP worker threads nice, fresh and clean. The longer a worker is allowed to furnish requests, more unstable it will get. There's also a higher risk of memory leaks.

Here's a nice overview of all the config options I mentioned here, as well as others: http://myjeeva.com/php-fpm-configuration-101.html

Hope these tips help you! Remember to tweak and observe, unfortunately there doesn't seem to be a rule of thumb for all this, there are too many variables that affect PHP's behaviour and stability.

Increasing FcgidMaxProcesses does not help to solve “mod_fcgid: can’t apply process slot” error

Issue is resolved now.

And problem was not related to FCGID or any other Apache module configuration.

The reason behind sudden deteriorating behaviour of server was attack Yes, that's right! Though it was not DDoS, but continuous requests of attacker with different query string patterns(SQL injection) and page load time of the targeted page - excluding query string parameter - is around 3 seconds resulted in hit for threshold limit of FCGID process.

I came to know about it when I enabled mod_status which directly highlighted such attempts to breach.

I blocked the IP of that user and within a minute all operations back to normal.

Best Answer

Related Solutions

Nginx – Constantly have to reload PHP-FPM

Increasing FcgidMaxProcesses does not help to solve “mod_fcgid: can’t apply process slot” error

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