KABLAMO

Monit - How to Know When Your Web Site Is Down

If your website goes down, you want to find out fast. There are a few ways to accomplish this, but I’m using monit. Monit is a mature unix monitoring daemon and it gives me the ability not only get alerts but to restart services that go down.

Monit has lotsa power and options and you can read about all of them on the man page. Or if you don’t want to mess around with that you can pay them for a pretty web admin interface and some phone/tablet apps for a one time fee of € 65. Another simpler and I think less powerful option is monitor.us.

I don’t want to pay. So I installed monit like this:

apt-get install monit

The configuration file for monit lives at /etc/monit/monitrc. You probably don’t need to bother with that. When monit runs, it looks in /etc/monit/conf.d and executes any scripts it finds in there. Like many people I’m running nginx in front of my Starman web apps. So I want monitor both of those processes.

Here is how to do that. Created a script named /etc/monit/confd/nginx:

check process nginx with pidfile /var/run/nginx.pid

    start program = "/etc/init.d/nginx start"
    stop  program = "/etc/init.d/nginx stop"

    alert kablamo@example.com with mail-format {
           from: monit@example.com
        subject: monit alert: $SERVICE $EVENT $DATE
        message: $DESCRIPTION
    }

    if failed port 80 protocol HTTP
        request /
        with timeout 7 seconds
        then restart

Then create a second script named /etc/monit/conf.d/mywebapp. Its very similar. This assumes you are running your web app as the user web on localhost port 22222.

check process mywebapp with pidfile /var/run/mywebapp.pid

    start program = "/etc/init.d/mywebapp start" as uid web and gid web
    stop  program = "/etc/init.d/mywebapp stop"  as uid web and gid web

    alert kablamo@example.com with mail-format {
           from: monit@example.com
        subject: monit alert: $SERVICE $EVENT $DATE
        message: $DESCRIPTION
    }

    if failed port 22222 protocol HTTP
        request /
        with timeout 7 seconds
        then restart

With these scripts, anytime your processes disappear or stop working you will get email and monit will try to restart them.

But I’m paranoid. So I created a third monit script to do an end to end test in case something ever gets misconfigured somewhere. /etc/monit/conf.d/end2end:

check host networthify.com with address 71.19.156.131

    alert kablamo@example.com with mail-format {
           from: monit@monit@example.com
        subject: monit alert: $SERVICE $EVENT $DATE
        message: $DESCRIPTION
    }

    if failed port 80 protocol HTTP
        request /
        with timeout 9 seconds
        then alert

Suggestions for improvment?