Posts Tagged ‘unreachable’

Auto restart Apache on High server load (bash shell script) – Fixing Apache server temporal overload issues

Saturday, March 24th, 2012

auto-restart-apache-on-high-load-bash-shell-script-fixing-apache-temporal-overload-issues

I've written a tiny script to check and restart, Apache if the server encounters, extremely high load avarage like for instance more than (>25). Below is an example of a server reaching a very high load avarage:;

server~:# uptime
13:46:59 up 2 days, 18:54, 1 user, load average: 58.09, 59.08, 60.05
load average: 0.09, 0.08, 0.08

Sometimes high load avarage is not a problem, as the server might have a very powerful hardware. A high load numbers is not always an indicator for a serious problems. Some 16 CPU dual core (2.18 Ghz) machine with 16GB of ram could probably work normally with a high load avarage like in the example. Anyhow as most servers are not so powerful having such a high load avarage, makes the machine hardly do its job routine.

In my specific, case one of our Debian Linux servers is periodically reaching to a very high load level numbers. When this happens the Apache webserver is often incapable to serve its incoming requests and starts lagging for clients. The only work-around is to stop the Apache server for a couple of seconds (10 or 20 seconds) and then start it again once the load avarage has dropped to less than "3".

If this temporary fix is not applied on time, the server load gets increased exponentially until all the server services (ssh, ftp … whatever) stop responding normally to requests and the server completely hangs …

Often this server overloads, are occuring at night time so I'm not logged in on the server and one such unexpected overload makes the server unreachable for hours.
To get around the sudden high periodic load avarage server increase, I've written a tiny bash script to monitor, the server load avarage and initiate an Apache server stop and start with a few seconds delay in between.

#!/bin/sh
# script to check server for extremely high load and restart Apache if the condition is matched
check=`cat /proc/loadavg | sed 's/\./ /' | awk '{print $1}'`
# define max load avarage when script is triggered
max_load='25'
# log file
high_load_log='/var/log/apache_high_load_restart.log';
# location of inidex.php to overwrite with temporary message
index_php_loc='/home/site/www/index.php';
# location to Apache init script
apache_init='/etc/init.d/apache2';
#
site_maintenance_msg="Site Maintenance in progress - We will be back online in a minute";
if [ $check -gt "$max_load" ]; then>
#25 is load average on 5 minutes
cp -rpf $index_php_loc $index_php_loc.bak_ap
echo "$site_maintenance_msg" > $index_php_loc
sleep 15;
if [ $check -gt "$max_load" ]; then
$apache_init stop
sleep 5;
$apache_init restart
echo "$(date) : Apache Restart due to excessive load | $check |" >> $high_load_log;
cp -rpf $index_php_loc.bak_ap $index_php_loc
fi
fi

The idea of the script is partially based on a forum thread – Auto Restart Apache on High Loadhttp://www.webhostingtalk.com/showthread.php?t=971304Here is a link to my restart_apache_on_high_load.sh script

The script is written in a way that it makes two "if" condition check ups, to assure 100% there is a constant high load avarage and not just a temporal 5 seconds load avarage jump. Once the first if is matched, the script first tries to reduce the server load by overwritting a the index.php, index.html script of the website with a one stating the server is ongoing a maintenance operations.
Temporary stopping the index page, often reduces the load in 10 seconds of time, so the second if case is not necessery at all. Sometimes, however this first "if" condition cannot decrease enough the load and the server load continues to stay too high, then the script second if comes to play and makes apache to be completely stopped via Apache init script do 2 secs delay and launch the apache server again.

The script also logs about, the load avarage encountered, while the server was overloaded and Apache webserver was restarted, so later I can check what time the server overload occured.
To make the script periodically run, I've scheduled the script to launch every 5 minutes as a cron job with the following cron:

# restart Apache if load is higher than 25
*/5 * * * * /usr/sbin/restart_apache_on_high_load.sh >/dev/null 2>&1

I have also another system which is running FreeBSD 7_2, which is having the same overload server problems as with the Linux host.
Copying the auto restart apache on high load script on FreeBSD didn't work out of the box. So I rewrote a little chunk of the script to make it running on the FreeBSD host. Hence, if you would like to auto restart Apache or any other service on FreeBSD server get /usr/sbin/restart_apache_on_high_load_freebsd.sh my script and set it on cron on your BSD.

This script is just a temporary work around, however as its obvious that the frequency of the high overload will be rising with time and we will need to buy new server hardware to solve permanently the issues, anyways, until this happens the script does a great job 🙂

I'm aware there is also alternative way to auto restart Apache webserver on high server loads through using monit utility for monitoring services on a Unix system. However as I didn't wanted to bother to run extra services in the background I decided to rather use the up presented script.

Interesting info to know is Apache module mod_overload exists – which can be used for checking load average. Using this module once load avarage is over a certain number apache can stop in its preforked processes current serving request, I've never tested it myself so I don't know how usable it is. As of time of writting it is in early stage version 0.2.2
If someone, have tried it and is happy with it on a busy hosting servers, please share with me if it is stable enough?

How to install and configure torbutton on Debian / Anonymizing Iceweasel, Firefox on Debian GNU/Linux

Thursday, August 5th, 2010

Tor Onion Logo

There is a quite a buzz online recently about the implications breach of personal privacy by simple browing online.
A week ago I've blogged On How to improve your web browser security for better personal identity
Though there is probably a plenty of more things to be done on guaranteeing your anonymous identity online, the article lacked to mention one very one vital project related with anonymity – the tor Anonymity online project
The project offer the user the right to be anonymous online through a complex constantly expanding network of volunteers which voluntary install and grant access to the installed tor server to be used as a proxy from their computers.
A very thorough explanation on what is tor can be red here
Enabling tor on your personal computer would at least guarantee you that every now and then your traffic browser network traffic (request) would flow through a random tor servers located on a different worldly geographic locations.
Usually the traffic to a destination host would pass through 5 tor network nodes. Where the traffic is unecrypted between last node and the 4th node, while in the other four ones it's completely crypted.
This makes your tracking almost impossible if it's based on technologies like for instance Maxmind's Geoip or Geonames's geographical data base because every now and then you'll appear to be coming to the end point referrar web server originating from a different tor node ip address

The tor server is a free software licensed under the GPL and this is also a good assurance because everybody is able to have a look on the code and this is a further guarantee that the software doesn't include a malicious ways for a middle users to sniff on your traffic.

The tor project has even built a pre-bundled browser ready to be worn by yourself on a usb stick, so you can quickly start using the tor anonymous network on any random computer anywhere.
The tor browser page is available here also Tor Browser Bundle for Windows is available here
Tor server is available for both Windows, Mac OS X, Linux and Linux/BSD Unix
Of course tor is not perfect it opens some other possible doors for attackers which are much less likely to occur if you don't use it, however in general it's better off with tor than without it.

One serious reason for not reason for not using Tor might be that it's usually many times slower than normal browser since, it routes traffic through a different tor network nodes.
So if you decide to go on and use it you better be patient and calm 🙂

Since I'm a Debian user and I really do value my privacy I decided to start using Tor.
In order to start using Tor it's usually necessary to configure your browser to use The TorButoon Firefox browserextension

Nevertheless on Debian GNU/Linux if you try to go the straigh way as explained on Tor's website install the TorButton and configure it to work in cooperation with the polipo caching proxy
You will be not able to browse after enabling straight the tor plugin.
If you try the up-mentioned approach you're probably about to come to errors like:
"the proxy server is refusing connections"
,
Proxy error: 502 Disconnected operation and object not in cache
or
504 Connect to superquizgames.com:80 failed: SOCKS error: host unreachableThe following error occurred while trying to access http://yourwebsite.com/:504 Connect to superquizgames.com:80 failed: SOCKS error: host unreachable

In order to properly install configure and enable the TorButton on my Debian GNU/Linux I had to get through the following steps:

1. Install the polipo caching proxy

debian:~# apt-get install polipo

2. Download and overwrite default polipo configuration with the one from torproject.org

This is necessary to configure in order to have polipo adapted to work with tor, so issue the following commands:

debian:~# cd /etc/polipo
debian:~# wget https://svn.torproject.org/svn/torbrowser/trunk/build-scripts/config/polipo.conf
debian:~# mv config config.bak
debian:~# mv polipo.conf config

3. Restart polipo for the new config settings to take affect

debian:~# /etc/init.d/polipo restart

4. Install the iceweasel-torbutton browser extension

debian:~# apt-get install iceweasel-torbutton

The iceweasel-torbutton will also install you the tor package which is evidently required for the torbutton to operate.
Now you should be ready to go, you can enable the tor use from the tor button which should appear in your browser in the bottom right corner of your browser.
It should look something similar to:

Tor Button screenshot in Iceweasel

Tor Enable/Disable Iceweasel browser Button

To test your Tor Configuration you can use the Test Settings button which is straight available from TorButton's preferences

From here after it might be a good idea to play with the TorButton security settings and configure it according to your liking, bear in mind that you should have a solid knowledge on how browsers work and some basic Internet protocols before you start tampering this options.
If tou don't know what you do you better stop and don't tamper with the torbutton security options.
The only one that you will most probably want to untick is The Disable plugins during Tor usage , stopping this option will allow you to have a flash video streaming display properly, otherwise you won't be able to use , Vbox etc.
Below you see a screenshot of the TorButton Security Settings dialog.

TorButton properties Dialog

To open up this dialog you need to navigate to the TorButto and choose preferences with the right mouse buttons 🙂
Hope this article is informative to somebody out there.
User feedback is mostly welcome! Cheers 🙂