Nginx & php Error in EC2 with LB

How can I know the correct numbers to input for the increase, or what is recommended?

I often calculate numbers using the following calculations.

pm.max_children = available memory of instance / average memory usage of php-fpm process

If you are using Linux, you can get the average memory used by the php-fpm process using the following command.

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

I often set "worker_connections" to about twice the number shown in the error. In your case, I think it would be a good idea to set it to around "1,536". Be careful not to set the number larger than "worker_rlimit_nofile". https://nginx.org/en/docs/ngx_core_module.html#worker_connections

It should be kept in mind that this number includes all connections (e.g. connections with proxied servers, among others), not only connections with clients. Another consideration is that the actual number of simultaneous connections cannot exceed the current limit on the maximum number of open files, which can be changed by worker_rlimit_nofile.

You can check the number of files that can be handled by the OS using the following command.

cat /proc/sys/fs/file-max

Therefore, I think it is best to calculate "worker_rlimit_nofile" as follows.

worker_rlimit_nofile = Number of files that can be handled by the OS / Number of Nginx processes