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monit service monitoring

Created by john. Last edited by alex, 352 days ago. Viewed 2,070 times. #8

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Monit is an application service monitor. It can tell you if your MySQL or Apache server has crashed, and even give it a swift kick to get it up and going again.

Compared to other service monitors I've looked at, Monit has good documentation, and a straightforward configuration.

It's available as a Debian package and there is an RPM here: http://dag.wieers.com/rpm/packages/monit/

On Debian, it won't start automatically after installing:

apt-get install monit
Reading package lists… Done
Building dependency tree… Done
The following NEW packages will be installed:
  monit
0 upgraded, 1 newly installed, 0 to remove and 0 not upgraded.
Need to get 0B/255kB of archives.
After unpacking 680kB of additional disk space will be used.
Selecting previously deselected package monit.
(Reading database … 58858 files and directories currently installed.)
Unpacking monit (from .../monit_1%3a4.8.1-2.1_i386.deb) …
Setting up monit (4.8.1-2.1) …
Starting daemon monitor: monit won't be started/stopped
        unless it it's configured
        please configure monit and then edit /etc/default/monit
        and set the "startup" variable to 1 in order to allow 
        monit to start

In /usr/share/doc/monit/README.Debian, your find some information about creating a monit_delay script to prevent monit from restarting services that are slow to come up on reboot.

Now all you need to do is go uncomment some things in the configuration file. You'll find that in /etc/monit/monitrc, or if you use the RPM, it's /etc/monit.conf

There are many options for configuring monit, here is what I uncommented to get a simple configuration working:

set daemon  120
set logfile syslog facility log_daemon
set mailserver localhost
set alert root@localhost
set httpd port 2812 and
use address localhost  # only accept connection from localhost
allow localhost        # allow localhost to connect to the server and
allow admin:stR0Ngpsswd       # require user 'admin' with password 'monit'

Instead of putting services in this same file, put them in /etc/monit.d, that way it's easy to turn off/on monitoring for a particular service.

Restart Apache

For testing Apache's status, it's standard practice to create an empty file or 'token' for Monit to request.

On Debian

mkdir /var/www/monit/
touch /var/www/monit/token

Paste this in your Apache configuration:

SetEnvIf        Request_URI "^/monit/token$" dontlog
CustomLog       logs/access.log common env=!dontlog

Then paste this in /etc/monit.d/apache.conf

start program = "/etc/init.d/apache2 start"
stop  program = "/etc/init.d/apache2 stop"
      if failed host 127.0.0.1 port 80 
              protocol HTTP request /monit/token then restart
      if 5 restarts within 5 cycles then timeout

Then edit /etc/default/monit

# You must set this variable for monit to start
startup=1

Startup monit

/etc/init.d/monit start

check that it's running and then for fun, lets stop apache:

ps aux | grep monit 
root     11583  0.0  0.7  20400  1248 ?        Sl   04:20   0:00 /usr/sbin/monit -d 180 -c /etc/monit/monitrc -s /var/lib/monit/monit.state
/etc/init.d/apache2 stop

In syslog you'll see something like this:

Jun 18 04:32:41 rimu monit[11583]: HTTP error: Server returned status 404 
Jun 18 04:32:41 rimu monit[11583]: 'apache2' failed protocol test [HTTP] at INET[127.0.0.1:80] via TCP 
Jun 18 04:32:41 rimu monit[11583]: 'apache2' trying to restart 
Jun 18 04:32:41 rimu monit[11583]: 'apache2' stop: /etc/init.d/apache2 
Jun 18 04:32:42 rimu monit[11583]: 'apache2' start: /etc/init.d/apache2

You can find many other configuration examples for MySQL, Mongrel and other popular applications, just google them up.

watch nginx

check process nginx with pidfile /var/run/nginx.pid
  start program = "/etc/init.d/nginx start"
  stop program = "/etc/init.d/nginx stop"
  if failed port 80 protocol HTTP request / then restart
  if 5 restarts with 5 cycles then timeout

watch mongrels

http://www.igvita.com/blog/2006/11/07/monit-makes-mongrel-play-nice/

http://software.pmade.com/blogs/ramblings/2006/12/27/mongrel-cluster-and-monit

http://rubyforge.org/pipermail/mongrel-users/2006-September/001359.html

watch a VirtualHost or remote URL

check host arbitrary_name with address real_url
  if failed port 80 proto http then alert

See the man page for more examples.

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