Monit System Linux

Welcome back to this next part in our series on setting up a high availability solution using the bottlecapdev.com BottleCap Development. You might be wondering why we are still here if we’ve managed to get the system up and running. The reason for this is that if a server fails the other will take over serving the web pages, but you would be unaware that it had done so unless you were manually checking on the servers. So this time we’ll be looking at setting up some automatic notifications for the server status using Monit.

Anyone who has done some reading about heartbeat may have noticed that it is also possible to have heartbeat send email notifications. Unfortunately the system will only mail out when the transition from one server to the other takes place. This means that should the secondary server fail while the primary is serving the website, you would not receive an email notification. The method we are going to use should be more complete, and will notify if one server should go away, but also if the web server stops serving files.

To start with, we will install monit itself, a simple task from the default repositories:

sudo apt-get install monit

 

With that installed, we’ll be looking at setting up some basic configuration, which is done in the /etc/monit/monit.rc file:

sudo nano /etc/monit/monitrc

Monit Service Manager

Monit has a relatively straightforward configuration format, and the file is heavily commented with examples and explanations. The main elements we want to set here are your mailserver settings and alert settings. Scroll to the bottom of the file and paste in the following lines:

set mailserver localhost

set alert you@yourdomain.com

 

You’ll need to change “you@yourdomain.com” to your own email address. You can also have multiple alert lines to email more than one address with alerts. If you installed iwatch previously, then it will have installed the postfix mail server for you, which means that we can use localhost to send the email alerts for you. If this isn’t installed and you don’t have a mail client on your server, then you can use a remote mail server instead by changing the mailserver line to:

set mailserver mail.yourdomain.com port 587

username “you@yourdomain.com” password “mypassword”

using tlsv1

with timeout 30 seconds

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Obviously for this to work you’ll need Monit to be logging into a valid email address at the mailserver for your emails to send. You’ll need to change the mailserver address, username and password to match the details you log in with to send email.

With your mailserver and alert destinations set, you can save and exit the file.

Next we need to create the configuration to monitor the servers. Configuration is stored in /etc/monit/conf-available, and we’ll start with a script to monitor that the website is up:

sudo nano /etc/monit/conf-available/website

 

Paste in the following, changing the IP address to your website’s domain name:

check host web-server with address 192.168.0.4

if failed port 80 protocol http with timeout 10 seconds then alert

Save and exit the file after making your changes. This will get monit to check that it can connect to your website, and will send an alert if it takes longer than 10 seconds to connect.

 

Next, we want to set up a ping test to each server directly to ensure they are online:

sudo nano /etc/monit/conf-available/partner-server

 

Paste in the following code, ensuring that on the first server the IP address used is that of the second server, and on the second that it is the first server’s IP. Change the hostname to match the server being tested – you can use your own names or firstserver/secondserver as you require.

check host firstserver with address 192.168.0.2

if failed icmp type echo

count 5 with timeout 5 seconds

2 times within 3 cycles

then alert

Save and exit the file. This file tells monit to ping the server, and if it doesn’t respond for 2 out of 3 checks to send an alert.

 

Finally, you need to enable the configuration. This is done by making a link from the files in conf-available to the conf-enabled directory. We’ll also add monitoring for the local MySQL and SSH servers while we are here:

sudo ln -s /etc/monit/conf-available/mysql /etc/monit/conf-enabled/

sudo ln -s /etc/monit/conf-available/openssh-server /etc/monit/conf-enabled/

sudo ln -s /etc/monit/conf-available/website /etc/monit/conf-enabled/

sudo ln -s /etc/monit/conf-available/partner-server /etc/monit/conf-enabled/

 

With those done, you can now restart Monit and the monitoring will start:

sudo systemctl restart monit

 

As with most of our guides in this series, you need to do this on both servers. Next time we’ll be rounding off with some final thoughts on the setup.

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