www.gavinwill.me.uk

Apache will normally serve a file at the maximum speed possible. I needed to rate limit an apache server to act as a fake QOS to ensure the line would not be saturated when serving large files. This is incredibly easy to do with mod_bw. First we need to install and enable mod_bw

 apt-get install libapache2-mod-bw
 a2enmod bw

Then it is a simple task of specifying the limits in you virtualhost conf file.

BandWidthModule On
ForceBandWidthModule On
BandWidth 10.40.0.0/16 0
BandWidth all 1500000

The above enables the module, forces the module for all apache traffic and then finally we dont restrict the local network but restrict everyone else to 150KB/s.

Then simply restart apache

/etc/init.d/apache2 restart

You can test by commenting out the line for the local network, restarting apache again and then try to download a large file and you should notice the browser is only about to download at around 150KB/s.

I had a requirement to ensure that a linux server was mounted to a windows share that was used for backups. Adding this check into Nagios was incredibly easy with a custom script and use the check_by_ssh command.

First I needed to create a script that would check if the mountpoint existed and then report back an exit code of 2 if it is mounted and an exit code of 0 if it was not mounted so Nagios can report accordingly.

 
test "`mount | grep windows.share`" ==  ""
if [ $? == 0 ]; then
echo " Windows Share Not Mounted.  Backups will fail "
exit 2
 
else
echo " Windows Share Mounted "
exit 0
fi

This script was then saved in /usr/local/bin as check_mount.sh and made executable.

On the Nagios Server I then created the simple custom command to run this script.

##############################################################################
# CUSTOM Check Linux Mounted to Backup Drive
#
##############################################################################
 
define command{
command_name    check_mount
command_line $USER1$/check_by_ssh -H $HOSTADDRESS$ -t 45 -C /usr/local/bin/check_mount.sh
}

Finally you then need to define the service for the check to occur.

define service{
        use generic-service
        host_name remoteserver
        service_description Backup Drive Mounted
        check_command check_mount
}

With the command now defined it is really easy to add any further monitoring of other linux servers that have a windows share mounted by simply copying the script over, amending it to suit and adding the extra host to the service description.

I am a massive fan of Nagios. Whilst it has an initial learning curve it can be an incredibly powerful system. Assuming you have a standardised naming structure for your servers, switches and other infrastructure you can use regular expressions to create a hostgroup that will cover all your devices.

define hostgroup {
    hostgroup_name  Domain Controllers
    alias           All Domain Controllers
    members ^.*dc[0-5]$,^.*(dev|prd|)$
}

If you run a logical structure and have lots of switches or servers this can be a really easy way to ensure you are monitoring all servers or switches and can easily be expanded by simply changing the regex.

Nagios is an amazing tool for monitoring and reporting and alerting of availability of hosts and services. I have typically only used simple SNMP checks or NRPE checks with a small agent installed on the remote host. I wanted to be able to measure a sites server room temperature via a USB probe that was on a remote box and installing NRPE or using SNMP was not an option. The only way to obtain the temperature was to run a command on the remote box. Thankfully Nagios has the inbuilt check_by_ssh command which allows nagios to connect up to a remote computer via ssh to then run the command. It does require SSH login via keys, thankfully this is also really easy to setup with ssh-keygen and ssh-copy-id.

It is important that these keys are generated as the user running nagios and a corresponding nagios user on the remote system.

On the Nagios server su into the running user for Nagios which will most likely be Nagios unless you have any customisations.

Run the command

ssh-keygen

This creates the public and private keys.

Copying the public key to the remote host is incredibly easy using ssh-copy-id

ssh-copy-id -i ~/.ssh/id_rsa.pub remote-host

ssh-copy-id appends the keys to the remote-host’s .ssh/authorized_key

Now simply test connecting via ssh by running the command

ssh remote-host

You should connect straight away without being prompted for any password. If this is the case you can now create a custom command and service in nagios to monitor the remote-host and obtain any values / information you require to monitor.