Celery can very well handle 100k tasks/sec. Celery is not locked in to Python, but you are right it's not a drop in solution for other languages as it doesn't

Celery can very well handle 100k tasks/sec. Celery is not locked in to Python, but you are right it's not a drop in solution for other languages as it doesn't support them natively (yet, but that will change soon). You can write simple workers for Celery in other languages too, and there is one in active development for Java. But then Redis is not really a good choice, AMQP is more convenient for interoperability. Have no idea if pinterest evaluated Celery, because they have not been in contact. If they did there are several pitfalls they could have gotten wrong at this scale, but I'm pretty confident it would have been more than suitable. It could have been a benefit for all of us and chances are they have underestimated the effort needed to maintain a custom solution.