Achieving Continuous Integration with Drupal
In the early 1990s, my first job out of college was as a software engineer at a startup company. We were building a commercial product using a well-known open-source network security project. In those days, Agile software development practices (not to mention the World Wide Web, or even widespread public awareness of the Internet) still were in the future. My fellow engineers on that project (who had just graduated with me and to this day are the best programmers I know) and I were taught what we now call the Waterfall method. We thought we were invincible.
We had no idea what was coming. After consultation with potential customers, we wrote a Requirements document describing what the product needed to do, a Functional Specification that described how the product would look and behave, a Design document that described the technical architecture and internals of how we would build it, and even a Test Plan that described the automated tests we would build to ensure the product worked. We had a release deadline, declared by management, of "before Christmas". Good thing we were so young! We engaged in our Death March. The local Chinese delivery place got to know us well. I got home around 1am every morning for months. We finally finished and shipped version 1.0 of the product on December 18. It took me a few weeks to remember what normal humans did when they were not at work.
What Did I Learn from This Experience?
What we did wrong: basically, everything about the software engineering methodology we used was completely stupid. We shipped a working product on time, but we started with the benefit of a working open-source project. We made essentially every mistake that Agile development was invented to prevent.
What we did right: we actually implemented our Test Plan. Since the tests were automated, the build process had to be automated. It certainly added a lot of "extra work" to the project, but the payoff was huge. Before we left for the day, we would kick off the build script. When we came in the next morning, if the last line of output said PASSED, we felt confident and ready to ship. We didn't know it at the time, but we were on the path of what eventually would be called Continuous Integration (CI).
Fast-forward 20 years. I'm now at Acquia, which produces commercial products for companies using the open-source project Drupal. Drupal is a LAMP-stack application for building Web sites and services. We realized early on that everyone using Drupal needs to host it somewhere, and that most people building sites with Drupal do not also want to have to become experts in building a reliable, scalable infrastructure for hosting it. More than that, they also want to be able to follow best practices in software development, testing and deployment; they want to use Continuous Integration. However, they often do not have the time, resources or management support to invest in the necessary infrastructure. I've spent the last three years addressing that problem.
What Is Continuous Integration?
Many excellent and persuasive resources on the Web talk about the principles of CI in detail. In this article, I discuss a simplified list of the most meaningful best practices for Drupal Web site development:
Use a source code repository. This is step zero for good software development. Most people are doing this, using Git, SVN or other systems; if you are not, start now.
Make small, frequent changes. All developers should commit their changes frequently. This reduces the inevitable conflicts and lets problems surface sooner. Also, small, frequent changes enable small, frequent releases, making all the rest of the principles more valuable.
Automate testing. Have your repository automatically integrated with a testing environment, so that every commit triggers a test run. This way, you know immediately if something broke.
Test in a clone of the production environment. It does no good to test your software under different conditions from those that it will run in production; doing so is a recipe for taking down your site when you deploy. Never hear someone say "But it worked on my machine!" again.
Make all versions easily accessible. Despite best efforts, production releases still will break, so you need an easy way to re-deploy a prior version. Then, you'll want to compare the working and broken versions to figure out what went wrong. To do this, you'll need a reference copy of past releases.
Have an audit trail (that is, a blame list). This helps you not just in the source control of who made this commit, but who deployed the commit as well. This can provide rationale as well as potential fixes.
Automate site deployment. In order to tolerate small, frequent releases, pushing a release needs to be an automated process so it's very quick and easy. If it's a big chore to push one release, the whole process falls apart.
Measure results and iterate rapidly. Are the changes helping? Is the site faster? Did the usability enhancement yield more sales? If it's not, you can iterate again.
Achieving Continuous Integration requires some amount of infrastructure, the culture and discipline of the engineering team to use it, and management's understanding and commitment so that it supports the necessary investment. This is an article about technology, not management and culture, so I focus primarily on the infrastructure here.
Building It Yourself
Many shops build their own CI systems that are perfectly tailored to their own needs. Doing so is perfectly reasonable if you have the time and resources to get there. The biggest danger of doing it yourself, of course, is deciding to—and then not getting around to it. You end up doing things the manual, slow and error-prone way "until we have time to fix it", which often turns out to be "never". When you do get started, it probably will end up being a permanent side project, which may lead you to cut corners that will end up causing problems at the worst possible time later.
Here are some of the things you should keep in mind.
Use a source code repository. You probably already are (right?). You will need to be familiar with its "post-commit hook" capability to script actions based on it. If you are using a hosted repository (such as GitHub), you will have to integrate with its Web-based hooks.
Make small, frequent changes. All of your developers will be making frequent commits, resolving conflicts locally as best they can. To keep things moving forward, you need to have a constantly available running copy of everyone's latest code. One way to do this is to deploy the tip of your main development branch automatically to a shared development environment, so everyone always can see it. You can script this yourself using your repo's post-commit hooks. A build automation tool like Jenkins will help, but you still need to write the deployment script yourself.
Automate testing. Assuming you write automated tests for your site, you will want to run them every time someone makes what they believe is a release-ready commit. Lots of tools exist for doing this. One popular choice is Jenkins (formerly called Hudson), and it is excellent. It can integrate directly with your code repository and trigger a "job" on every commit, or run a job on a schedule.
The tests themselves are not the whole story though. Because your application is a Drupal site, you need to test it in a Web environment. You'll certainly need a running database server. If you want to test actual page loads like a browser would see, you'll need a running Web server too. You probably want to test your application along with a reasonably current production database; if you don't automate that, one day you'll find yourself testing against year-old data. However, you also probably want to "scrub" your current production database before running tests against it, lest you accidentally spam all your customers from your test servers, or worse. This is all the responsibility of your test harness script, run by Jenkins.
If you fool yourself that you can "mock out" these dependencies and have purely standalone unit tests that can run anywhere, reality will mock you back. You will discover that tests are not accurately simulating your live environment, and you will have to roll back a release that "passed all of its tests" but failed in production.
Test in a clone of the production environment. This is where things really get interesting. I've already talked about needing a running Web and database server. If your site uses additional services like memcached, Varnish or Apache Solr, you need to make sure those are in place too. If your production site uses SSL, you either need SSL running in your testing environment, or you need to turn off the checks or redirection that enforces it. Ultimately, it is as much work to maintain your test environment as it is your production environment.
Barry Jaspan is a serial software engineer and entrepreneur who has been creating and selling open-source software products literally since he was 12 years old (many moons ago!).
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