The idea of using a service which can generate partial updates for Firefox has been around for years. We actually used to have a server called Prometheus that was responsible for generating updates for nightly builds and the generation was done as a separate process from actual builds.
Scaling that solution wasn't easy and we switched to build-time update generation. Generating updates as a part of builds helped with load distribution, but lacked of flexibility: there is no easy way to generate updates after the build, because the update generation process is directly tied to the build or repack process.
Funsize willl solve the problems listed above: to distribute load and to be flexible.
Funsize is split into several pieces:
REST API fronted powered by Flask. It's responsible for accepting partial generation requests, forwarding them to the queue and returning generated partials.
Celery-based workers to generate partial updates and upload them to S3.
SQS or RabbitMQ to coordinate Celery workers.
One of the biggest gains of Funsize is that it uses a global cache to speed up partial generation. For example, after we build an en-US Windows build, we ask Funsize to generate a partial. Then a swarm of L10N repacks (almost a hundred of them per platform) tries to do a similar job. Every single one asks for a partial update. All L10N builds have something in common, and xul.dll is one of the biggest files. Since the files are identical there is no reason to not reuse the previously generated binary patch for that file. Repeat 100 times for multiple files. PROFIT!
The first prototype of Funsize lives at github. If you are interested in hacking, read the docs on how to set up your developer environment. If you don't have an AWS account, it will use a local cache.
Note: this prototype may be redesigned and switch to using TaskCluster. Taskcluster is going to simplify the initial design and reduce dependency on always online infrastructure.