Posts Tagged ‘virtual hosts’

Check and Restart Apache if it is malfunctioning (not returning HTML content) shell script

Monday, March 19th, 2012

Check and Restart Apache Webserver on Malfunction, Apache feather logo

One of the company Debian Lenny 5.0 Webservers, where I'm working as sys admin sometimes stops to properly server HTTP requests.
Whenever this oddity happens, the Apache server seems to be running okay but it is not failing to return requested content

I can see the webserver listens on port 80 and establishing connections to remote hosts – the apache processes show normally as I can see in netstat …:

apache:~# netstat -enp 80
Active Internet connections (w/o servers)
Proto Recv-Q Send-Q Local Address Foreign Address State User Inode PID/Program name
tcp 0 0 xxx.xxx.xxx.xx:80 46.253.9.36:5665 SYN_RECV 0 0 -
tcp 0 0 xxx.xxx.xxx.xx:80 78.157.26.24:5933 SYN_RECV 0 0 -
...

Also the apache forked child processes show normally in process list:

apache:~# ps axuwwf|grep -i apache
root 46748 0.0 0.0 112300 872 pts/1 S+ 18:07 0:00 \_ grep -i apache
root 42530 0.0 0.1 217392 6636 ? Ss Mar14 0:39 /usr/sbin/apache2 -k start
www-data 42535 0.0 0.0 147876 1488 ? S Mar14 0:01 \_ /usr/sbin/apache2 -k start
root 28747 0.0 0.1 218180 4792 ? Sl Mar14 0:00 \_ /usr/sbin/apache2 -k start
www-data 31787 0.0 0.1 219156 5832 ? S Mar14 0:00 | \_ /usr/sbin/apache2 -k start

In spite of that, in any client browser to any of the Apache (Virtual hosts) websites, there is no HTML content returned…
This weird problem continues until the Apache webserver is retarted.
Once webserver is restarted everything is back to normal.
I use Apache Check Apache shell script set on few remote hosts to regularly check with nmap if port 80 (www) of my server is open and responding, anyways this script just checks if the open and reachable and thus using it was unable to detect Apache wasn't able to return back HTML content.
To work around the malfunctions I wrote tiny script – retart_apache_if_empty_content_is_returned.sh

The scripts idea is very simple;
A request is made a remote defined host with lynx text browser, then the output of lines is counted, if the output returned by lynx -dump http://someurl.com is less than the number returned whether normally invoked, then the script triggers an apache init script restart.

I've set the script to periodically run in a cron job, every 5 minutes each hour.
# check if apache returns empty content with lynx and if yes restart and log it
*/5 * * * * /usr/sbin/restart_apache_if_empty_content.sh >/dev/null 2>&1

This is not perfect as sometimes still, there will be few minutes downtime, but at least the downside will not be few hours until I am informed ssh to the server and restart Apache manually

A quick way to download and set from cron execution my script every 5 minutes use:

apache:~# cd /usr/sbin
apache:/usr/sbin# wget -q http://www.pc-freak.net/bscscr/restart_apache_if_empty_content.sh
apache:/usr/sbin# chmod +x restart_apache_if_empty_content.sh
apache:/usr/sbin# crontab -l > /tmp/file; echo '*/5 * * * *' /usr/sbin/restart_apache_if_empty_content.sh 2>&1 >/dev/null

 

How to list enabled VirtualHosts in Apache on GNU / Linux and FreeBSD

Thursday, December 8th, 2011

How Apache process vhost requests picture, how to list Apache virtualhosts on Linux and FreeBSD

I decided to start this post with this picture I found on onlamp.com article called “Simplify Your Life with Apache VirtualHosts .I put it here because I thing it illustrates quite well Apache’s webserver internal processes. The picture gives also a good clue when Virtual Hosts gets loaded, anways I’ll go back to the main topic of this article, hoping the above picture gives some more insight on how Apache works.;
Here is how to list all the enabled virtualhosts in Apache on Debian GNU / Linux serving pages:

server:~# /usr/sbin/ apache2ctl -S
VirtualHost configuration:
wildcard NameVirtualHosts and _default_ servers:
*:* is a NameVirtualHost
default server exampleserver1.com (/etc/apache2/sites-enabled/000-default:2)
port * namevhost exampleserver2.com (/etc/apache2/sites-enabled/000-default
port * namevhost exampleserver3.com (/etc/apache2/sites-enabled/exampleserver3.com:1)
port * namevhost exampleserver4.com (/etc/apache2/sites-enabled/exampleserver4.com:1)
...
Syntax OK

The line *:* is a NameVirtualHost, means the Apache VirtualHosts module will be able to use Virtualhosts listening on any IP address (configured on the host), on any port configured for the respective Virtualhost to listen on.

The next output line:
port * namevhost exampleserver2.com (/etc/apache2/sites-enabled/000-default Shows requests to the domain on any port will be accepted (port *) by the webserver as well as indicates the <VirtualHost> in the file /etc/apache2/sites-enabled/000-default:2 is defined on line 2 (e.g. :2).

To see the same all enabled VirtualHosts on FreeBSD the command to be issued is:

freebsd# pcfreak# /usr/local/sbin/httpd -S VirtualHost configuration:
wildcard NameVirtualHosts and _default_ servers:
*:80 is a NameVirtualHost
default server pc-freak.net (/usr/local/etc/apache2/httpd.conf:1218)
port 80 namevhost pc-freak.net (/usr/local/etc/apache2/httpd.conf:1218)
port 80 namevhost pcfreak.afraid.org (/usr/local/etc/apache2/httpd.conf:1353)
...
Syntax OK

On Fedora and the other Redhat Linux distributions, the apache2ctl -S should be displaying the enabled Virtualhosts.

One might wonder, what might be the reason for someone to want to check the VirtualHosts which are loaded by the Apache server, since this could be also checked if one reviews Apache / Apache2’s config file. Well the main advantage is that checking directly into the file might sometimes take more time, especially if the file contains thousands of similar named virtual host domains. Another time using the -S option is better would be if some enabled VirtualHost in a config file seems to not be accessible. Checking directly if Apache has properly loaded the VirtualHost directives ensures, there is no problem with loading the VirtualHost. Another scenario is if there are multiple Apache config files / installs located on the system and you’re unsure which one to check for the exact list of Virtual domains loaded.