Cesar Chew at 17:47, 24 November 2014

2014-11-24T17:47:01Z

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{{Cat|Apache|02}}

<slideshow style="nobleprog" headingmark="⌘" incmark="…" scaled="true" font="Trebuchet MS" >
;title: Apache workers
;author: Sam Bashton (NobleProg Ltd)

</slideshow>
=== Apache worker model ⌘===
* Apache can function using different models
* Most common - prefork
=== Apache prefork ⌘===
* One central Apache process to accept incoming connections, read configuration etc
* Multiple child processes to serve requests
* Each child can serve only one request at a time
=== Apache prefork settings ⌘===
```
StartServers 8
MinSpareServers 5
MaxSpareServers 20
ServerLimit 256
MaxClients 256
MaxRequestsPerChild 4000
```
=== Tuning Apache prefork ⌘===
* StartServers
:* Number of Apache processes to create on first start
* MinSpareServers
:* Minimum number of spare Apache processes that should be available at any time. If less spare workers than this are available, Apache will start more
* MaxSpareServers
:* Maximum number of spare workers.If more than this are available, Apache will kill them off at a rate of 1/second to bring it below this.
=== Tuning Apache prefork ⌘===
* Default EL5 config has a maximum of 256 child processes
* This means maximum 256 concurrent requests
* In reality, 256 may well be too high
* When using PHP, Apache processes are often 30MB+
* 30 * 256 = 7680MB of RAM required, just for workers
* Under these conditions, 256 MaxClients suitable only for machines with at 8GB RAM
=== Sizing MaxClients ⌘===
* Tool ps_mem.py can be used
:* http://www.pixelbeat.org/scripts/ps_mem.py
:* Shows actual RAM in use by each process
:* Should be used on a server with a representative workload
* Set MaxClients too high, and you'll start swapping
=== What are the workers doing? ⌘===
* Apache module `mod_status` shows this data
* Module is loaded by default but not enabled
* Uncomment the section in /etc/httpd/conf/httpd.conf to enable
:* Change `.example.com` to `127.0.0.1`
* Once enabled, run `service httpd fullstatus` to see data
=== Exercise ⌘===
* Enable mod_status and find the status of each worker
* How much memory is each httpd process using on your VM?
* What is a suitable value for MaxClients on this VM based on the above?

Apache workers - Revision history

Cesar Chew at 17:47, 24 November 2014