Think shell

So recently I went nuts having to login onto each server to look at its munin graphs. While you have few servers it’s doable, but managing large farms and checking up on them while having to login into each is just pain in the ass.
So what to do?
Hey… let’s make a central munin server, and let’s hold all the graphs there. That way we can review them all with just one user name and password, we can compare host performances, etc…
To accomplish this we will need one server for centralized graphs (could be a low budget dedicated server or a small vps), apache installed on central munin server, munin-node installed on all other server we wish to monitor.

Installing munin

So this will be a minimal install for a central munin server. I’m using a small vps with minimal centos install.
First let’s setup elrepo

Now we need to install munin and munin-node (if you wish to monitor this host as well).

by default munin will put its html files into /var/www/html/munin folder
If you wish to move that to another place, now is your time. For the sake of simplicity I’ll just leave it where it is.
Of course we will need apache to access those munin html files, so if you don’t have apache installed do:

now start the apache

If you left everything as it is munin html should be available at:

http://yourhostname.com/munin/

You may notice that there is nothing there yet, just wait until we configure all other hosts.
start the munin-node on this host (if you installed it)

Make sure your cron is runing

and let’s go configure those other hosts.

Installing munin-node

Installing on cPanel

Since lot’s of my servers to monitor are with cPanel installed there is an easy way to install munin.

Login to your whm go to: Manage plugins, now find Munin, click a check box, scroll down and click save.
After the munin is installed it should appear in your whm at the bottom of the navigation.
Go and check up if the munin is installed correctly.

Installing trough cPanel will install munin-node and munin, you can disable the munin graphing later if you like.

Installing on non cPanel

We can install munin on Centos trough Elrepo.
first we will setup elrepo

and then install a munin-node:

voila… let’s configure nodes on remote servers now.

Configuring munin-node on remote hosts

For both cPanel and non-cPanel servers all we need to do is add allowed host in munin-node.conf

add at the end of the file:

where 192.168.0.20 is the ip address of you central munin server.
restart the munin-node:

If you have firewall installed on that host (and I hope you do), allow the incoming tcp port 4949 for the ip of the central node.

In csf add the following line:

to your /etc/csf/csf.allow file
or just run:

Modify this to your firewall, and don’t forget to replace 192.168.0.20 with your munin server
Now everything should be ready for data collection from central server

Configuring munin server

All we need to do now is to configure the munin

If you didn’t change any locations of html files and munin datastore you realy don’t need to change that in the conf file.

What we are interested with are the host sections. You will notice there is configuration for our localhost
You can change its name now, leave the address field as it is.

To add up a new host just add:

change the 192.168.0.10 with the ip of the server you wish to monitor.
you can now add as many host you like.
Make sure that you have enabled outgoing connections on tcp port 4949 on your central munin server.
After a while the first results should start to appear.

Configuring multi host display graphs

The real benefit of having all the host graphs and data on one place is you can easily make multi host graphs and compare the loads on the servers. This could help you grasp a bigger picture of individual server workloads and give you an idea what to improve and how to load balance between the machines.

Here is one of the example graphs, showing apache request per second. If the machines were the same hardware configuration that would give indications that some of the machines have higher hit rate and we would need to rewrite our load balancing.

We could do the same thing with load graphs and see which servers have the spikes, and distribute the workload on some less loaded servers.

So how do we configure this?

First you need to find out rrd’s name of the data you wish to put on the graph.

for example apache accesses per second:

ls -lh in the directory and you will find out what data is available to munin.
in case of the apache accesses data we will have few files named:

hostname.domainname.com-apache_accesses-accesses80-d.rrd
hostname2.domainname.com-apache_accesses-accesses80-d.rrd

what we are interested with are those fields (marked in red) after the domain name separated by dash.
Ok let’s write a conf in munin.conf for this two hosts.

Go under the host definitions in your conf file and add:

[domainname.com;Totals]
update no
apacheaccess.graph_title Apache access side by side
apacheaccess.graph_order hostname=hostname.domainname.com:apache_accesses.accesses80 hostname1=hostname1.domainname.com.com:apache_accesses.accesses80

Notice the red lines, they are the same as rrd filenames red parts we saw earlier, just replace dash with dot.
Green text is to disable updates for this domain declaration since updates are already done at the host declaration in the conf file. Blue is the graph representation name, followed by title in the first line and data in second.

This way you can make all the side by side graphs for all the data munin collected in rrd files. After the changes wait for a next munin update and enjoy the graphs

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