Tuesday, November 17, 2009

Monitoring multiple MySQL instances with Munin

I've been using Munin for its resource graphing capabilities. I especially like the fact that you can group servers together and watch a common metric (let's say system load) across all servers in a group -- something that is hard to achieve with other similar tools such as Cacti and Ganglia.

I did have the need to monitor multiple MySQL instances running on the same server. I am using mysql-sandbox to launch and manage these instances. I haven't found any pointers on how to use Munin to monitor several MySQL instances, so I rolled my own solution.

First of all, here is my scenario:
  • server running Ubuntu 9.04 64-bit
  • N+1 MySQL instances installed as sandboxes rooted in /mysql/m0, /mysql/m1,..., /mysql/mN
  • munin-node package version 1.2.6-8ubuntu3 (installed via 'apt-get install munin-node')
Step 1

Locate mysql_* plugins already installed by the munin-node package in /usr/share/munin/plugins. I have 5 such plugins: mysql_bytes, mysql_isam_space_, mysql_queries, mysql_slowqueries and mysql_threads. I don't use ISAM, so I am ignoring mysql_isam_space_.


Step 2

Make a copy of each plugin for each MySQL instance you want to monitor. I know this contradicts the DRY principle, but I just wanted something quick that worked. The alternative is to modify the plugins and add extra parameters so they refer to specific MySQL instances.

For example, I made N + 1 copies of mysql_bytes and called them mysql_m0_bytes, mysql_m1_bytes,..., mysql_mN_bytes. In each copy, I modified the line "echo 'graph_title MySQL throughput'" to say "echo 'graph_title MySQL throughput for mN'". I did the same for mysql_threads, mysql_queries and mysql_slowqueries. So at the end of this step I have 4 x (N+1) new plugins in /usr/share/munin/plugins.


As I said, the alternative is to modify for example mysql_bytes and add new parameters, e.g. a parameter for the title of the graph. However, I don't know exactly how the plugin is called from within Munin, and I don't want to fiddle with the number and order of parameters it's called with -- which is why I chose the easy way out.

Step 3

Create symlinks in /etc/munin/plugins to the newly created plugins. Example:

ln -s /usr/share/munin/plugins/mysql_m0_bytes /etc/munin/plugins/mysql_m0_bytes

(and similar for all the other plugins).


Step 4

Specify the path to msyqladmin for the newly defined plugins. You do this by editing the plugin configuration file /etc/munin/plugin-conf.d/munin-node.

Here's what I have in this file related to MySQL:

[mysql_m0*]
user m0
env.mysqladmin /mysql/m0/my sqladmin

[mysql_m1*]
user m1
env.mysqladmin /mysql/m1/my sqladmin

[mysql_m2*]
user m2
env.mysqladmin /mysql/m2/my sqladmin

[mysql_m3*]
user m3
env.mysqladmin /mysql/m3/my sqladmin

What the above lines say is that for each class of plugins starting with mysql_mN, I want to use the mysqladmin utility for that particular MySQL instance. The way mysql-sandbox works, mysqladmin is actually available per instance as "/mysql/mN/my sqladmin".

Note that the naming convention is important. The syntax of the munin-node plugin configuration file says that the plugin name "May include one wildcard ('*') at the start or end of the plugin-name, but not both, and not in the middle." Trust me, I haven't read this fine print initially, and I named my new plugins something like mysql_bytes_mN, then tried to configure the plugins as mysql_*mN. Pulling hair time ensued.

Step 5

Restart munin-node via 'service munin-node restart'. At this point you're supposed to see the new graphs under the Mysql link corresponding to the munin node where you set all this up. You should see N+1 graphs for each type of plugin (mysql_bytes, mysql_threads, mysql_queries and mysql_slowqueries). The graphs can be easily differentiated by their titles, e.g. 'MySQL throughput for m0' or 'MySQL queries for m1', etc.

One other quick tip: if you want to easily group nodes together, come up with some domain name which doesn't need to correspond to a real DNS domain name. For example, I called my MySQL servers something like mysqlN.myproject.mydomain.com in /etc/munin/munin.conf on the Munin server side. This allows me to see the myproject.mydomain.com group at a glance, with all the metrics for the nodes in that group shown side by side.

Here's how I defined each node in munin.conf:

[mysqlN.myproject.mydomain.com]
 address 192.168.0.N
 use_node_name yes

(where N is 1, 2, etc)

3 comments:

Julien. said...

Hello !

Did you try :

ln -s /usr/share/munin/plugins/mysql_bytes /etc/munin/plugins/mysql_m0_bytes

etc ?
That way you keep one single script but 'symlinked' multiple times, if you glance at the munin snmpd_ plugins that's how it does. And actually they pass informations to the munin node by the symlink name, ex : snmp__if_eth0 symlink of
/usr/share/munin/plugins/snmp__if_ (traffic for the eth0 interface) etc.

Grig Gheorghiu said...

Hi, Ju -- thanks for the tip. No, I haven't tried that, but I'll try it and report back here.

Grig

Unknown said...

This is extremely useful to me. Thanks a lot for posting this.

Modifying EC2 security groups via AWS Lambda functions

One task that comes up again and again is adding, removing or updating source CIDR blocks in various security groups in an EC2 infrastructur...