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Deploying Sensu monitoring on Heroku

Sensu - trying to unsuck monitoring

Some months ago I wanted to set up monitoring for a handful of servers I use for personal stuff. As a first solution Nagios came to mind. However for several reasons I didn’t want to set it up and configure it. And I really didn’t want to dedicate an existing server to do monitoring or get a new one just for that purpose. Around that time I also read about Sensu, a new approach to monitoring, which is a result of Nagios not being a good fit for the monitoring needs at Sonian. Its technology stack is Ruby, Redis and AMQP. I immediately thought it should be possible to put this on the Heroku Cedar stack and run it on an instance there, which would make a nice solution for monitoring a small number of systems. So I hacked away and with a lot of help (and patience) from Sean Porter, the adaptions to make the server and API part of Sensu deployable on Heroku are in the new 0.9.6 release.

Setting up the Sensu repository

In order to get started and configure your Sensu instance, clone the example repository from Github.

    git clone

The example includes a basic folder layout for running a server or API instance on Heroku. All configuration files can be dropped in the config/ folder. They will be picked up by the process when Sensu starts. The example repo also includes a basic handler (bin/showme.rb), which prints event data to STDOUT. There are a lot more handlers in the Sensu community plugins repository on Github. Since handlers are just ruby scripts, you can download the handlers you want and also put it in the bin/ directory. Don’t forget to add the correct configuration file for the handler in the config/ directory also. A great overview how to configure Sensu can be found on Joe Miller’s blog and there is also an official install guide.


In order to deploy Sensu to Heroku, you need to create two apps. One will be the Sensu API instance and the other one the Sensu server. It doesn’t really matter, which one you start with. The important thing is, that you only need to add the RabbitMQ and Redis plugins once and can then reuse the settings on the second instance.

So create the first instance on the cedar stack from within the example repo and add the plugins:

    heroku create --stack cedar awesome-sensu-server
    heroku plugins:install redistogo
    heroku plugins:install rabbitmq
    heroku config:add API_PORT=80

You have to add the API_PORT environment variable to the server instance, since otherwise it will assume it’s running the API itself and assign the instance locale port from the PORT environment variable to use as the API port. After that is done, push the code to Heroku and scale up a worker process:

    git push heroku master
    heroku ps:scale app=1

For the API instance create a new branch in the repo or clone the example repo into a new location. Then initialize the API:

    heroku create --stack cedar awesome-sensu-api
    heroku config:add REDISTOGO_URL="value from server instance"
    heroku config:add RABBITMQ_URL="value from server instance"

Now change the Procfile to start up the API instead of the Sensu server like this:

    app: sensu-api -v -c config/config.json -d config/

Commit the changes and push it to the Heroku app:

    git push heroku-api master
    heroku ps:scale app=1

Now all you have to do is set up clients and voila, you have Heroku hosted monitoring. If you’re not yet familiar with setting up clients, I highly recommend Joe Miller’s blog again. He’s a strong contributor to Sensu and has written an abundance of blog posts and tutorials about it. And of course there is also the sensu wiki.

Further improvements

A definite improvement for plugins and handlers would be to be able to also read configuration from environment variables. At the moment the way to go is to add a configuration JSON file in the config folder. This is fine except for the fact that you’d also have API keys commited to the repo.

And obviously more bugs will probably come up, once more people run Sensu on Heroku. I’ve been running a low volume instance for a couple of weeks now and it works pretty great so far.