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rtyler

Even a failed experiment teaches you something

The most recent Jenkins security advisory contains a fix for an issue in the GitHub Authentication plugin. One which I reported many moons ago, during an experiment I named “Code Valet.” Seeing the issue finally resolved brought fond memories back into my mind and I realized that I have never really reflected and shared what it was and more importantly: why it failed. At it’s core, Code Valet was intended to solve two fundamental problems: firstly, I wanted a Jenkins Pipeline as a Service, since I find Jenkins Pipeline to be a very useful tool, which I wanted for all my open source projects. Secondly, the Jenkins project needed to shift its footing towards a continuous feedback and continuous delivery model. Code Valet aimed to solve both of these problems.

Years ago, CloudBees had tried to run “Jenkins as a Service” with its now (finally!) defunct “DEV@Cloud” service, or in a different manner with Kohsuke’s “Buildhive” project. DEV@Cloud provided users with a full Jenkins installation, which I believe was part of its undoing. The essential balancing act of developer tools is that we must provide our customers with enough power and flexibility, but not so much that they shoot themselves in the foot. Providing a full Jenkins installation to many people is not only giving them the gun, but loading it, pointing it at their foot, and then daring them not to shoot. Jenkins is powerful but unfortunately it can become unwieldy and a support nightmare. “Jenkins Pipeline as a Service” meant something different to me, Code Valet would allow users to run Pipelines but not actually administer the instance. In fact, I made explicit design choices to prevent end-users from even seeing too much behind the curtains of Code Valet. I consider myself an expert at configuring and operating Jenkins, and everything in Code Valet was tuned appropriately for the users already, nothing on an administrative level was necessary. In fact, the user experience was also intentionally locked into Blue Ocean, and it was actually impossible to do anything but create Pipelines and run them. For my own open source projects this was perfect, I could easily add a Jenkinsfile to my GitHub repositories, and things just worked!

In order to address the second problem, Code Valet’s Jenkins image was bleeding edge. Not in the way Jenkins Evergreen is bleeding edge, but more Gentoo Linux-style. Jenkins core was built daily from the HEAD of the master branch. The batteries-included plugins were also all built daily from their respective master branches. The Git plugin, Azure VM Agents plugin, Pipeline plugins, everything in the system was the absolute latest. As you may have guessed, this resulted in dozens of interesting build and runtime failures, all of which were reported upstream. For the first time, I had an environment which was providing “real world” SaaS-style feedback, using Sentry on real Jenkins workloads.

Code Valet operated as an interesting experiment out of the CloudBees CTO office for 4-5 months before I ultimately shut it down. There was nothing more to learn, and it was clear Code Valet did not have any immediate future within the CloudBees product roadmap.

Lessons

For my taste, that bleeding edge turned out to be a little too bloody. I filed two dozen tickets for various plugins, some of which were addressed very quickly, and others remained open for weeks, some still remain open. Rapid feedback is only useful with rapid(ish) iteration. Like many large and federated open source communities, the Jenkins project suffers a bit from uneven levels of investment across the plugin ecosystem. For example, while Microsoft’s developers were very responsive to issues discovered in their Azure plugins, another plugin integral to Code Valet was maintained by one person who might address issues once in a while if work wasn’t too hectic. By no means do I fault maintainers for not being responsive for volunteer projects, but building a complex system from components with disparate levels of maturity can be painful. Fortunately, many of pains from release management with Code Valet went on to inform and improve the design of what came after: Jenkins Evergreen.

Before I built Code Valet, I could have likely filled half a book with thoughts and practices on good security for Jenkins. Originally designed with internal development teams in mind, running Jenkins on a hostile network like the public internet is an uphill battle, updating default configuration settings, disabling functionality to reduce the attack surface area, and ensuring security best practices are being enforced and adhered to by the users. In the case of Code Valet, everything got far more challenging.. Combine the existing lock down procedures for a Jenkins on the public internet, and then add the requirement to lock down Jenkins far beyond what it natively supports in order to provide users with that limited “Jenkins Pipeline as a Service” experience. I ended up writing a significant amount of Groovy code to configure and adjust settings throughout Jenkins, as Configuration as Code didn’t yet exist. At times this still wasn’t enough, and I resorted to clever container or nginx hacks to disable, hide, or otherwise obfuscate certain aspects of Jenkins’ behavior. All of these hacks I still consider to be rather clever, but trying to reduce the surface area of Jenkins is an endless struggle. The system yearns to be extended in new and different ways, so it’s a constant game of whack-a-mole trying to close things up. Locking down Jenkins Pipeline alone is arguably an impossible task, something not even my silly Pipeline Shared Library hacks could manage.

The cost model for Code Valet was never something I expected to be net-positive. In discussions I would refer to it as a “loss leader”, something to drive adoption of Jenkins Pipeline with a calculated user acquisition cost. Still, Code Valet was deployed onto Kubernetes (AKS) and very intentionally restricted to reduce overhead and per-user cost wherever possible. Tightly packing Jenkins master containers into Kubernetes, and then dynamically provisioning Azure VM and container agents for workloads remain design patterns I stand by for cheaply running Jenkins-as-a-Service, but Jenkins is undoubtedly huge. I could not get decent performance in a low enough memory and CPU footprint for Code Valet not to be a loss leader. And while Kohsuke’s Buildhive project was, if I recall, running one big multi-tenant Jenkins instance, Code Valet by design used per-user instances. The exact numbers I cannot remember, but I spent my time thinking of more and more novel yet non-invasive ways to reduce the monthly cost per user. Looking across the market today, it is evident how punishing the race to the bottom for price on CI-as-a-Service products has been. Most vendors spend a non-trivial amount of time finding ingenious ways to arbitrage with AWS Spot Instances or other means of shaving pennies off compute-hours where possible. This was all very competitive even before GitHub Actions showed up on the scene and dropped the bottom out of the market entirely. In my opinion, developer tools has always been a challenging market to work in. Developers inherently undervalue their tools, recognizing the importance of a $3000 laptop or a $1000 chair to our daily productivity, we still balk at $15/month services or licenses which would otherwise improve our lives.

Early in 2018, CloudBees acquired Code Ship, bringing onboard a great product and engineering team, but also a pretty good CI-as-a-Service offering. While Code Ship doesn’t speak Jenkins Pipeline, it was already quite a mature product with significant market traction, helping close the book on the Code Valet experiment.


The CI/CD landscape in 2019 is littered with various forms of declarative and turing-complete YAML. I still find myself wanting a Jenkins Pipeline as a Service because I still fervently believe that Pipeline is a good tool. The modelling capacity is better than anything else, and the extensibility options are superb, whether with Shared Libraries, or a variant my pal James Dumay prototyped which never made it out of the lab. That said, running a large Jenkins infrastructure no longer appeals to me. There’s a very good reason why CloudBees builds and sells their CloudBees Core product: scaling Jenkins CI/CD as a service is hard. For something intended to be generally available like Code Valet, I would now argue that it is impossible to do with off-the-shelf Jenkins.

The direction Pipeline is heading, driven by one of the chief architects of Jenkins Pipeline Andrew Bayer, is looking more and more parseable. That may leave the door open to alternative execution engines for Jenkins Pipeline in the future. To me that is key for a descendant of Code Valet. With an execution engine designed for the needs of a Pipeline-as-a-Service offering, Jenkins Pipeline would more easily be supported from a security, maintainability, and cost standpoint.

Ultimately I think the biggest lesson I learned from Code Valet was to think bigger. I started out using Jenkins as the runtime for Code Valet because Blue Ocean already existed, Jenkins Pipeline already existed, all these things were built already, albeit for a very different purpose. I intentionally steered away from building a new engine because I figured it would be too much work. Some months after I first created Code Valet, I ended up writing a parser for Jenkins Pipeline’s Declarative syntax and a basic execution engine. While neither were complete, I was surprised with how little effort it took to build the engine from scratch, compared to the effort required to reduce Jenkins to something smaller.

Rather than trying to use a swiss-army knife as a sword, it may be a better idea to melt it down and simply forge anew.