Redhat – Basic Apache httpd server setup becomes slow to serve images requiring frequent restart

apache-2.2httpdhttpd.confperformanceredhat

I have an Apache httpd server running on RHEL 5.3. I'm using this server to serve static content (images) to for a website running on another httpd instance. In the public web directory are several images, and that is all. Some time after startup, the server becomes very slow to serve images to the browser, and can often hang for several minutes whilst trying to serve a 16×16 png.

What is the best way to go about debugging this problem?

I've run top on the box to verify that there is enough free memory, and CPU available. The machine isn't going into swap, and the httpd process only takes up CPU and memory for a couple of seconds when the image is requested through the browser. However the image is only returned often after several minutes.

A restart of the httpd process resolves the issue, and the images load quickly.

This seems like the simplest setup of a web server possible. What could the issue be?

Thanks

UPDATE: httpd.conf settings:

Timeout 10
KeepAlive On
MaxKeepAliveRequests 150
KeepAliveTimeout 15
ServerLimit 3

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

Best Answer

A couple questions:

Have you done any tuning to the Apache.conf file? Which Apache MPM are you using?
What parameters are currently set in the Apache.conf file for:

Timeout
KeepAlive
MaxKeepAliveRequests
KeepAliveTimeout
MinSpareServers
MaxSpareServers
StartServers
MaxClients
MaxRequestsPerChild

Related Solutions

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You're running out of swap because you're using all your RAM and then some. You have a serious problem that you need to rectify right now.

You have two choices: ignore cause and just add more RAM, or target the problem of what's actually munching on your memory.

Adding RAM is fairly cheap and fairly easy if it's your server but it's a temporary fix and if it's a VPS or a rented server, it's not so cheap. Let's have a go at fixing the root problem instead. What's sucking in that much memory? Here are a few tips:

Turn off InnoDB (unless you need it) in MySQL
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Consider a smaller httpd like cherokee, lighttpd or nginx (they're really fast and eat almost no RAM). Main downside is you can't use .htaccess files but you can hard-code in their functionality.
Are you using an OP-code cache for PHP? Try turning it off or switching to another, more efficient one.

In terms of just getting swap items back into real RAM, you can do that by:

swapoff -a && swapon -a

But don't try then when you've got less free memory than you have things in swap. It'll crash your server.

Linux – Fine tunning of Apache 2 MPM Prefork module parameters

You are going to run out of ram before you will be able to server a Million requests. How large are you apache client processes? I bet over 10MB (probably 25MB). You server could probably only handle 250 clients if the clients were only 10MB.

Might try lighttpd with fast-cgi.

To answer you question you would need to edit the mpm.conf files /etc/apache2/modules.d/00_mpm.conf for me, but im on gentoo so it will be a bit diffrent depending on the distro of linux you are using. But in that config there is a secion for prefork

Here is mine for a server with 12Gb of ram. (and we load balance the sites of 20 identical servers)

<IfModule mpm_prefork_module>
        StartServers            100
        MinSpareServers          5
        MaxSpareServers         200
        ServerLimit             375
        MaxClients              375
        MaxRequestsPerChild      0
</IfModule>

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