Over the course of the past couple days, I've been experimenting with some ideas with my "PentaGram" project, and I think I've made enough progress to write a follow-up blog post.
It's worth mentioning now that the commits to the repository have a lot of commentary in the commit messages and are meant to help guide you along step-by-step.
I do recommend opening the linked commit messages in a separate window and check them out as you follow along at home.
In order to best emulate a true outside-in workflow, I started with this
which really just added the
apphost.feature file mentioned in the previous
Feature: Serve the PentaGram web application In order to serve up PentaGram (and satanic phots) to millions of devil worshippers As an operations engineer App hosts should be configured to run the PentaGram web application
As you might expect, this by itself is pretty useless so I wrote out the first scenario and committed that too.
I should mention now that between just about every commit, and at every step of the way I was both running Cucumber and RSpec.
In order to realistically test the Puppet code underlying the entirety of the
apphost.feature, I needed to spin machines up and down rapidly, so I
integrated another one of my projects:
Blimpy. Since this was very
experimental, the majority of my first few hours of work on PentaGram was
consumed making the first couple steps in the scenario work:
Scenario: Provision a fresh app host Given an empty host And the host is to become a PentaGram app host When I provision the host
At this point I was ready to start driving the code necessary make the "When I provision the host" step run correctly. This required me to do a couple things:
Unfortunately as you can see here getting rspec-puppet up and running properly can be a little bit of work. I found out as I started to look at pulling in third party modules to manage things such as Apache, that I needed to create symlinks for them inside my "pentagram-web" module in order for rspec-puppet to find them properly.
With these dependencies being pulled into my "pentagram-web" module, I felt ready to step back out into Cucumber land.
What I found out when I ran the Cucumber scenario again, and actually provisioned the machine, was that the Passenger module required some more dependencies to be installed! Sure, I could have found this out by actually reading the full documentation on the Passenger module, but who has time for that these days? I addressed this in this commit, which was a good reminder that it doesn't matter how good your RSpec is, there's nothing quite like actually running your code.
Once everything was provisioning "mostly" properly, I was left to jump back "out" to Cucumber and implement the last two step definitions:
Then it should be running a web server And it should be responding to web requests
I thought about how best to implement this, and decided on the most simple
solution (in my opinion): ssh into the box and look! The reason I went for this
approach was to keep things simple, I could have made web requests to the
machine, but I wanted to focus on the bare minimum needed to pass the test. For
the first step I executed "
pgrep httpd" and made sure it returned a zero exit
code. For the second step, I invoked
localhost and made sure
that it could connect properly.
What I found out when I implemented these two steps was that...I actually was failing my Cucumber! In another great example of there being no substitute for running the code, I discovered an unspecified dependency in the Puppet resource graph between the Passenger module and Apache, which was fixed in this commit. Even though Puppet was provisioning the host correctly, it was failing to correctly start Apache, and thus failed the scenario!
The most important lesson I learned in this exercise was that you must execute your Puppet against a real machine before going to production. Correctly parsing Puppet, passing puppet-lint and rspec-puppet checks is not enough, it must execute on a machine or else you're really just guessing that it will work in production.
A couple weeks ago when I wrote about Puppetizing OpenGrok I mentioned using "Tinker Driven Development." At the time I really didn't know anything about OpenGrok or how I would manage it with Puppet. I am more convinced now that if I had taken an "outside-in" appraoch with the puppet-opengrok module, I would have been able to actually use Behavior/Test Driven Development. Even though I really didn't know anything about how OpenGrok worked, I knew what behavior I wanted from the system.
Provisioning isn't the end. In my previous post, I talked about "Operations as a stake-holder" which for this level of "outside-in" I think is fine, but in the end, Operations is a part of a greater organization. Even though the code implemented thus far provisons an app host which has effectively everything it needs to run PentaGram, it's not actually running PentaGram. From the "business perspective" I still haven't done anything! There's no PentaGram app running, there's no deployment happening, we're still not satisfying our users' need to post daemonic photos! I'm sure this can be fleshed out in additional scenarios that could be addressed after I met the needs of the Operations group.
It's clearer to me now where outside-in for Operations fits in the overall scheme of things. I can very easily imagine sitting down with an Operations Manager and discussing what needs to be done to "make PentaGram production ready" and in doing so, writing out the features and scenarios mentioned in the previous post.
There's still some tooling work that I think needs to be done to make this easier, but I'm optimistic about the future of behavior-driven operations!