Assistance with Apache Tuning on LAMP Stack

I'm looking for a little guidance and specific directives for tuning apache2 on a web server instance. Background:

I'm running a PHP/MYSQL-based web app on a Digital Ocean droplet with the following specs: 48 GB / 16 CPU Ubutnu LAMP stack. (160 GB SSD for the app files and OS, in case it matters/helps.)

Right now, the [url removed, login to view] directive is NOT well configured at all, and Apache2 is often very slow, sometimes returning timeout errors, during periods of heavy load. This is the current configuration that was on the app server when I took it over:

ServerLimit 5000

<IfModule mpm_prefork_module>

StartServers 5

MinSpareServers 5

MaxSpareServers 10

MaxClients 5000

MaxRequestsPerChild 0

</IfModule>

<IfModule mpm_worker_module>

StartServers 5

MinSpareServers 5

MaxSpareServers 10

MaxClients 5000

MaxRequestsPerChild 0

</IfModule>

The max CPU utilisation only ever seems to get to around 65% before apache2 crashes, though all available connections seem to be used up before that.

Here's a quick TOP dump (first N lines), so you can see the relative size of each apache2 process:

PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND

1089 mysql 20 0 8727952 119624 7876 S 145.7 0.2 2:21.73 mysqld

85 root 20 0 0 0 0 S 12.4 0.0 0:08.10 ksoftirqd+

7 root 20 0 0 0 0 S 7.2 0.0 0:08.51 rcu_sched

10 root 20 0 0 0 0 S 6.5 0.0 0:03.21 rcuos/2

267 root 20 0 0 0 0 S 4.9 0.0 0:06.04 jbd2/vda1+

6492 www-data 20 0 325144 14660 6620 S 4.2 0.0 0:01.58 apache2

8 root 20 0 0 0 0 S 3.9 0.0 0:03.45 rcuos/0

20 root 20 0 0 0 0 S 3.9 0.0 0:03.10 rcuos/12

23 root 20 0 0 0 0 S 3.9 0.0 0:03.20 rcuos/15

18 root 20 0 0 0 0 S 3.6 0.0 0:03.08 rcuos/10

6214 www-data 20 0 325040 14504 6468 S 3.6 0.0 0:00.90 apache2

12 root 20 0 0 0 0 S 3.3 0.0 0:02.78 rcuos/4

7229 www-data 20 0 325144 14464 6432 S 3.3 0.0 0:00.86 apache2

7513 www-data 20 0 325144 14636 6596 S 3.3 0.0 0:01.16 apache2

7698 www-data 20 0 325156 14672 6628 S 3.3 0.0 0:01.17 apache2

13 root 20 0 0 0 0 S 2.9 0.0 0:02.73 rcuos/5

What I'd like to get from you is directive on how to tune/modify apache to maximise performance on the hardware available and, in the event that resources are fully constrained, simply reject connections -- versus allowing the server to become overwhelmed so quickly, along with a little documentation/detail as to how you arrived at the suggestions. Nothing more than a quick email and copy/pasteable [url removed, login to view] directives are needed.

Also, one more note: The connections can be closed as soon as apache is done with them -- there's no need to keep connections alive for any period of time.

Apache Linux PHP Ubuntu

Project ID: #11529274

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