Azure PHP App Service - Change pm.max_children setting

Question

I'm seeing in the logs for my PHP app service the following message:

WARNING: [pool www] server reached pm.max_children setting (5), consider raising it

From doing a but of searching it seems like having the max_children value at 5 is pretty low. It seems the default for most PHP installations is 20. Is there a way to change this number with in the app service?

Thanks!

Answer 1

Hi @Alec Dhuse ,

Thanks for the question. You're correct the default max_children setting is 20. what version of PHP are you using?

Based on the solution found here, "you need to find your php-fpm.conf or www.conf depending on what version of PHP-FPM you have installed. for example edit /etc/php/7.0/fpm/pool.d/www.conf. You’ll want to look for the following settings and make adjustments based on your server specs:

[php-fpm-pool-settings]  
pm = dynamic  
pm.max_children = 25  
pm.start_servers = 10  
pm.min_spare_servers = 5  
pm.max_spare_servers = 20  
pm.max_requests = 500  

Depending on the name of your service, you can try on of the following:

sudo systemctl restart php-fpm  

sudo systemctl restart php7.0-fpm  

the following command will help us to determine the memory used by each (PHP-FPM) child process:

ps -ylC php-fpm --sort:rss  

You can check an average memory usage by single PHP-FPM process with this command:

ps --no-headers -o "rss,cmd" -C php-fpm | awk '{ sum+=$1 } END { printf ("%d%s\n", sum/NR/1024,"M") }'  

Hope that helps. Please let us know if you have further questions.

Thanks,
Grace

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Answer 2

@Grmacjon-MSFT

Do you have feedback in regards this being PHP 8 and not 7 as used in your example

Also, any idea about my question regarding the teir in scope, what amount of request one should in theory expect a P1v3 app should be able to handle?

Answer 3

As of now (september 23) the proper way is to set the FPM_* configuration variables understood by Oryx, see here. Be careful: invalid configurations (for example setting FPM_MIN_SPARE_SERVERS greater than FPM_MAX_CHILDREN) will result in a startup failure of the php-fpm pseudo service.

Overriding the www.conf configuration file of the default WWW pool is futile: at startup, AppService will just override it silently. Rehashing (i.e. kill -HUP) the PHP-FPM daemonized process is also wrong (it will just crash the webapp).

Should you need more customization, e.g. a more specific www.conf you are advised to bake your own Docker image and deploy that.