Ubuntu Gutsy - Apache configuration #1

Let's take a look at the main apache2.conf and ports.conf for our Ubuntu Gutsy install.

We're not actually going to change a lot at this point, just look at the main settings and see what they mean and what a change will actually do


Defaults

Why no specific changes to the default? Well, it's difficult to give a definitive configuration as there are so many variables to consider such as expected site traffic, Slice size, site type, etc.

However, we'll discuss the main settings and you can make any decisions as to what settings you feel are best for your site.

My advice is very simple: experiment. Find what works best on your setup.

ports.conf

Open the ports.conf file:

sudo nano /etc/apache2/ports.conf

The default entry is:

Listen 80

<IfModule mod_ssl.c>
    Listen 443
</IfModule>

Well, that seems fair enough. Port 80 is the standard HTTP port to listen on and if you have the ssl module loaded, then it will also listen on port 443 (HTTPS)

Unless you are using a custom port for experimentation, leave the defaults as they are (we'll look at SSL certificates and implementing HTTPS in another article).

apache2.conf

Open up the main Gutsy Apache config file:

sudo nano /etc/apache2/apache2.conf

I won't list the contents here but, if you are not familiar with the settings, have a read of the comments. I find them very informative and straight to the point.

Let's look at some of the main settings and what they mean:

Timeout

Default:

Timeout 300

This sets (in simple terms) the maximum time, in seconds, to wait for a request, action it and the response to the request.

The default is deliberately set high to allow for varied situations. You can reduce this to something more sane, such as 45 or even lower. A decrease may also help in reducing the effects of a DOS attack.

KeepAlive

Default:

KeepAlive On

Keep this set at 'On' as it allows for persistent connections to a client so each file, image, etc is not requested with a new connection. This allows for more efficiency. Define the KeepAlive settings as shown below:

MaxKeepAliveRequests

Default:

MaxKeepAliveRequests 100

Now we have our persistent connection, set the maximum number of requests per connection. Keep this high more maximum efficiency. If you have a site with images, javascripts, etc, try increasing this to 200.

KeepAliveTimeout

Default:

KeepAliveTimeout 15

So how long does the persistent connection wait for the next request? The default setting is very high and can easily be reduced to 2 or 3 seconds. If no new requests are received during this time the connection is killed.

What does this mean? Well, once a connection has been established and the client has requested the files needed for the web page, this setting says "sit there and ignore everyone else until the time limit is reached or you get a new request from the client".

Why would you want a higher time? In cases where there will be a lot of interactivity on the site. However, in most cases, people will go to a page, read it for a while and then click for the next page. You don't want the connection sat there doing nothing and ignoring other users.

prefork MPM

During the Apache install we selected apache2-mpm-prefork and not apache2-mpm-worker. If you want to know more about the differences between the two I will point you towards the official Apache docs (which are actually very good).

Default:

<IfModule mpm_prefork_module>
    StartServers                  5
    MinSpareServers           5
    MaxSpareServers          10
    MaxClients                    150
    MaxRequestsPerChild   0
</IfModule>

Again, it's difficult to give a suggestion here as to what is best for your site but, most the time, they can be left at the defaults.

StartServers: number of child server processes created at startup

MinSpareServers: minimum number of child server processes not doing anything (idle).

MaxSpareServers: maximum number of child server processes not doing anything (idle) - any more than the maximum will be killed.

Don't set Max lower than Min but Apache will ignore silly numbers here and set the Max at Min+1.

MaxClients: sets the maximum simultaneous requests that Apache will handle. Anything over this number will be queued until a process is free to action the request.

MaxClients is not the same as the maximum number of visitors you can have. It is the maximum requests.

Remember the KeepAliveTimeout? This was set low so the next request can be actioned but the original (now 'idle') client will still be sat there reading your webpage - the new (active) request will be actioned or, if the MaxClients limit has been reached, will be queued ready for the next available process.

In most cases, the client is not 'active'. Take this page. You requested it (using an active process) and then spent a while reading it which uses no processes - you are 'idle' (as far as the server is concerned!).

MaxRequestsPerChild: sets how many requests a child process will handle before terminating. The default is zero, which means it will never die.

Why change this if the Max numbers are set as shown above? Well, it can help in managing your Slice memory usage.

If you change the default you give a child a finite number of actions before it will die. This will, in effect, reduce the number of processes in use when the server is not busy. Thus freeing memory.

Freeing it for what though? If other software needed memory then it would also need it when the server is under load. It is unlikely you will have anything that requires memory only when the server is quiet.

Summary

Quite a lot here but as you go through the different settings you will see that the theory is quite simple. Naturally, there is a lot more to it than this article (or set of articles) can go into.

In the second apache2.conf article we will look at other settings that will add some more efficiency and help in increasing the security of our Slice.

PickledOnion.

Article Comments:

joshhunt commented Fri Feb 15 08:56:21 UTC 2008:

There is a typo:

"Feeing it for what though" should be "Freeing it for what though"

PickledOnion commented Fri Feb 15 10:34:47 UTC 2008:

Hey,

Thanks - I've changed it.

PickledOnion

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