Conduit Field Report, March 2017

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For background on Conduit, please see the previous post and the Intent to Implement.

Autoland

We kicked off Conduit work in January starting with the new Autoland service. Right now, much of the Autoland functionality is located in the MozReview Review Board extension: the permissions model, the rewriting of commit messages to reflect the reviewers, and the user interface. The only part that is currently logically separate is the “transplant service”, which actually takes commits from one repo (e.g. reviewboard-hg) and applies it to another (e.g. try, mozilla-central). Since the goal of Conduit is to decouple all the automation from code-review tools, we have to take everything that’s currently in Review Board and move it to new, separate services.

The original plan was to switch Review Board over to the new Autoland service when it was ready, stripping out all the old code from the MozReview extension. This would mean little change for MozReview users (basically just a new, separate UI), but would get people using the new service right away. After Autoland, we’d work on the push-to-review side, hooking that up to Review Board, and then extend both systems to interface with BMO. This strategy of incrementally replacing pieces of MozReview seemed like the best way to find bugs as we went along, rather than a massive switchover all at once.

However, progress was a bit slower than we anticipated, largely due to the fact that so many things were new about this project (see below). We want Autoland to be fully hooked up to BMO by the end of June, and integrating the new system with both Review Board and BMO as we went along seemed increasingly like a bad idea. Instead, we decided to put BMO integration first, and then follow with Review Board later (if indeed we still want to use Review Board as our rich-code-review solution).

This presented us with a problem: if we wouldn’t be hooking the new Autoland service up to Review Board, then we’d have to wait until the push service was also finished before we hooked them both up to BMO. Not wanting to turn everything on at once, we pondered how we could still launch new services as they were completed.

Moving to the other side of the pipeline

The answer is to table our work on Autoland for now and switch to the push service, which is the entrance to the commit pipeline. Building this piece first means that users will be able to push commits to BMO for review. Even though they would not be able to Autoland them right away, we could get feedback and make the service as easy to use as possible. Think of it as a replacement for bzexport.

Thanks to our new Scrum process (see also below), this priority adjustment was not very painful. We’ve been shipping Autoland code each week, so, while it doesn’t do much yet, we’re not abandoning any work in progress or leaving patches half finished. Plus, since this new service is also being started from scratch (although involving lots of code reuse from what’s currently in MozReview), we can apply the lessons we learned from the last couple months, so we should be moving pretty quickly.

Newness

As I mentioned above, although the essence of Conduit work right now is decoupling existing functionality from Review Board, it involves a lot of new stuff. Only recently did we realize exactly how much new stuff there was to get used to!

New team members

We welcomed Israel Madueme to our team in January and threw him right into the thick of things. He’s adapted tremendously well and started contributing immediately. Of course a new team member means new team dynamics, but he already feels like one of us.

Just recently, we’ve stolen dkl from the BMO team, where he’s been working since joining Mozilla 6 years ago. I’m excited to have a long-time A-Teamer join the Conduit team.

A new process

At the moment we have five developers working on the new Conduit services. This is more people on a single project than we’re usually able to pull together, so we needed a process to make sure we’re working to our collective potential. Luckily one of us is a certified ScrumMaster. I’ve never actually experienced Scrum-style development before, but we decided to give it a try.

I’ll have a lot more to say about this in the future, as we’re only just hitting our stride now, but it has felt really good to be working with solid organizational principles. We’re spending more time in meetings than usual, but it’s paying off with a new level of focus and productivity.

A new architecture

Working within Review Board was pretty painful, and the MozReview development environment, while amazing in its breadth and coverage, was slow and too heavily focussed on lengthy end-to-end tests. Our new design follows more of a microservice-based approach. The Autoland verification system (which checks users permissions and ensures that commits have been properly reviewed) is a separate service, as is the UI and the transplant service (as noted above, this last part was actually one of the few pieces of MozReview that was already decoupled, so we’re one step ahead there). Similarly, on the other side of the pipeline, the commit index is a separate service, and the review service may eventually be split up as well.

We’re not yet going whole-hog on microservices—we don’t plan, for starters at least, to have more than 4 or 5 separate services—but we’re already benefitting from being able to work on features in parallel and preventing runaway complexity. The book Building Microservices has been instrumental to our new design, as well as pointing out exactly why we had difficulties in our previous approach.

New operations

As the A-Team is now under Laura Thomson, we’re taking advantage of our new, closer relationship to CloudOps to try a new deployment and operations approach. This has freed us of some of the constraints of working in the data centre while letting us take advantage of a proven toolchain and process.

New technologies

We’re using Python 3.5 (and probably 3.6 at some point) for our new services, which I believe is a first for an A-Team project. It’s new for much of the team, but they’ve quickly adapted, and we’re now insulated against the 2020 deadline for Python 2, as well as benefitting from the niceties of Python 3 like better Unicode support.

We also used a few technologies for the Autoland service that are new to most of the team: React and Tornado. While the team found it interesting to learn them, in retrospect using them now was probably a case of premature optimization. Both added complexity that was unnecessary right now. React’s URL routing was difficult to get working in a way that seamlessly supported a local, Docker-based development environment and a production deployment scenario, and Tornado’s asynchronous nature led to extra complexity in automated tests. Although they are both fine technologies and provide scalable solutions for complex apps, the individual Conduit services are currently too small to really benefit.

We’ve learned from this, so we’re going to use Flask as the back end for the push services (commit index and review-request generator), for now at least, and, if we need a UI, we’ll probably use a relatively simple template approach with JavaScript just for enhancements.

Next

In my next post, I’m going to discuss our approach to the push services and more on what we’ve learned from MozReview.

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