Using RSpec to monitor your apps

RSpec did it again. It blew my mind. Just when I was doubting how awesome it was.

At Skylines we run a lot of services. API’s, websites, apps. You name it. When something goes down we want to know about it. Not when a client calls but the second after it breaks.

As a good developer you write a bunch of (unit/integration) tests. These tests are used when writing the code. But when the code is deployed all bets are off.

Our applications have a lot of moving parts and when one breaks that impacts our user experience. We want to monitor the experience our users are getting. It our API still up? Does it return valid JSON? Contains the JSON returned the fields we expect it to hold?

These questions sounded eerily like your run of the mill RSpec tests. I saw two problems with RSpec. Unlike regular tests we wanted to run tests continuously on live applications. Also RSpec just outputs on the console whether or not a test failed, we want to receive emails/texts when stuff breaks.

Turns out these aren’t problems at all! Years ago David wrote about the metadata properties you could pass to a describe or it method. Turns out this is ideally suited for what we want. Flag an example (or example group) as being a live test:

describe "live tests", :run_live do
  it "should return a 200 status code" do
    response = Curl::Easy.http_get("http://google.com")
    example.metadata[:live][:time_to_first_byte] = response.start_transfer_time
    response.header_str.should =~ /200 OK/
  end

  it "should return valid JSON"
  it "should have some fields in the JSON"
end

And in spec_helper.rb:

config.after(:each, :run_live => true) do |example_group|
  #do whatever you like with the exception and possible metadata
  example_group.example.exception
  example_group.example.metadata[:live]
end

All we need now is a daemon on some random server which checks out every repo we have and periodically run:

$ rspec -t run_live

Happy.