After languishing for a few years, Pulse got a burst of interest and development in 2014. Since I first heard of it, I’ve found the idea of a central message bus for the goings-on in Mozilla’s various systems rather intruiging, and I’m excited to have been able to grow it over the last year.
Pulse falls into that class of problem that is a result of, to borrow from a past Mozilla leader, our tendency to make our lives difficult, that is, to work in the open. Using RabbitMQ as a generic event stream is nothing special; Mozilla’s use of it as an open system is, I believe, completely unique.
Adapting a system intended for private networks into a public service always results in fascinating problems. Pulse has a decent permission-control system, but it’s not designed for self service. It is also very trusting of its users, who can easily overwhelm the system by just subscribing to streams and never consuming the messages.
The solution to both these problems was to design a management application: PulseGuardian. Via Persona, it handles account management, and it comes with a service that monitors Pulse’s queues. Since we presume users are not malicious, it sends a friendly warning when it notices a queue growing too large, but if ignored it will eventually kill the queue to save the system.
If you build it, they will come, or so says some movie I’ve never seen, but in this case it appears to be true. TaskCluster has moved whole-hog over to Pulse for its messaging needs, and the devs wrote a really nice web app for inspecting live messages. MozReview is using it for code-review bots and autolanding commits. Autophone is exploring its use for providing Try support to non-BuildBot-based testing frameworks.
Another step for Pulse beyond the prototype phase is a proper library. The existing mozillapulse Python library works decently, aside from some annoying problems, but it suffers from a lack of extensibility, and, I’m beginning to believe, should be based directly on a lower-level amqp or RabbitMQ-specific Python package and not the strange, overly generic kombu messaging library, in part because of the apparent lack of confirm channels in kombu. We’re looking into taking ideas from TaskCluster’s Pulse usage in bug 1133602.