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Sensu monitoring and Flapjack

Posted by Marius Voila on November 07, 2014 in London, U.K . — 0 comments This post contains 672 words

While researching for a monitoring notification routing & event processing system, I came across Flapjack, an alert notification router that works with check execution engines like Nagios and Sensu. Despite Sensu having built in notification and rollup, using these features can have various drawbacks that aren’t immediately apparent. The latest iteration(1.0) of Flapjack was built from the ground up to focus on alert routing. The Unix philosophy of doing one thing and doing it well really appeals to me, so I decided to look into this tool more and implement it in production.

In my case, I’m integrating Flapjack with Sensu instead of Nagios, so there is no need for the Nagios receiver. Instead, Sensu will be configured to feed check events directly into the Redis queue that is processed by Flapjack.

Installing Flapjack:

$ echo "deb precise main" > /etc/apt/sources.list.d/flapjack.list
$ apt-key adv --keyserver --recv-keys 8406B0E3803709B6
$ apt-get update && apt-get install flapjack

The Flapjack omnibus package includes its own instance of Redis on port 6380 so will not interfere with your Sensu Redis so you can run Flapjack on the same server. You’ll need to adjust /etc/flapjack/flapjack_config.yaml to fit your needs regarding email, sms, gateways, jabber and the email templates.

On the Sensu server, we need to install the Flapjack handler:

$ git clone git://
$ cp sensu-community-plugins/extensions/handlers/flapjack.rb /etc/sensu/extensions

Create /etc/sensu/conf.d/flapjack.json with the following contents. It should match the configuration used by Flapjack to connect to its own Redis.

  "flapjack": {
    "host": "localhost",
    "port": 6380,
    "db": "0"

Let’s take the ActiveMQ check from example and add flapjack as handler.

  "checks": {
    "activemq_watch_check": {
      "command": "/etc/sensu/plugins/ -w 1 -c 2 -q my.secret.swat.queue",
      "interval": 30,
      "subscribers": ["activemq_watch"],
      "handlers": ["hipchat", "flapjack"]

After restarting the Sensu server, you should be able to see check results flowing into the Flapjack web interface on port 3080 or via the API on port 3081. If you want to test out a failure, you can either use the /opt/flapjack/bin/flapjack simulate tool included with Flapjack, or create some havok yourself with service activemq stop (I would NOT recommend to stop a service if in Production).

Adding users can be done via the web interface or via the API (I prefer the API because is more fun and easier to automate :-) )

This is an example on how to add an user and a media contact via the API:

First we create a user.json file with the following content:

    "contacts": [
        "first_name": "Marius",
        "last_name": "Voila",
        "email": "",
        "timezone": "Europe/London",
        "tags": [
          "doing DevOps before I even knew DevOps was a thing"

Then we run (this assumes you have httpie installed) :

$ http POST < contacts.json


In this post, I introduced Sensu service checks and integrating them with Flapjack. There is a lot more configuration that needs to be done to make Flapjack useful, but I won’t get to in-depth on that topic. There is already a Wiki containing more instructions.