Linux Web Server Hack – How to Write Automated Load Balancing Script!

max — Tue, 23 Sep 2008 16:15:14 +0000

Well, I have been manually managing the dedicated server for this site for last 2 years or so but I found a better way to automate the server so it doesn’t ever go down due to overload.

One of the common problems in dedicated servers is the fact that load can go out of control and your web server along with it, causing you to hard-restart the server.

A better way to deal with this over-load problem is to shut down the HTTPD server (web server) before your server load gets to something around 2 to 5.

When the server load drops under 2, the script then can restart the server.

By doing this, you save a lot of headaches especially if you get “digged” or simply need the site up as much as possible.

Believe it or not, there’s no script that does this available free online so I made one for all you webmasters:

#!/bin/bash loadavg=`uptime | awk '{print $9}'` RESTART="/sbin/service httpd restart" # bash doesn't understand floating point # so convert the number to an interger thisloadavg=`echo $loadavg|awk -F \. '{print $1}'` if [ "$thisloadavg" -ge "5" ]; then echo "Busy - Load Average $loadavg ($thisloadavg) " httpd -k stop elif [ "$thisloadavg" -le "2" ]; then echo "Okay - Load Average $loadavg ($thisloadavg) " pgrep httpd if [ $? -ne 0 ] # if apache not running then # restart apache $RESTART echo "restart!" else echo "no restart!" fi else echo "waiting...!" fi

Save this code somewhere such as /root/checkload.sh.

Then add the following to your cron job. (/etc/cron.d/sa-update for Fedora Linux)

*/1 * * * * root sh /root/checkloadsh

This will run the script every 1 minute to check the load and if load is too high, web server will be turned off, if it’s lower than 2 and web server is off, it will turn the web server on.

There’s a lot of things that can go wrong with your web server whether from extra traffic or whatnot, but this script will be handy and I do recommend it to anyone who’s having trouble with high-load web servers that go down often. (like this blog)

Now, go install this script, you will never have to worry about your web server dying from high load ever again.

You can also change the value of “2″ in the code to something higher such as 5 or 10, which will wait longer to shut the web server off if load goes high.

I didn’t write the code from scratch, I took 2-3 different scripts and mixed it up so here’s the resources I used for the code:

Load Average Script – This one is the main skeleton I used

Check/Restart HTTPD Script – This one I used to check HTTPD server before trying to restart it.

Cron Task Scheduler – I keep forgetting that the most left number is the minutes, darn.

NOTE – This is a simple solution to keep your dedicated server running on 1 server (like this one), if you can afford more servers, you will need to resort to load balancing the “servers”, load balancing here refers to balancing within 1 server.

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Linux Web Server Hack – How to Write Automated Load Balancing Script!

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Linux Web Server Hack – How to Write Automated Load Balancing Script!

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