[dub]

> A surprising number of systems exhibit this behavior, sadly.

I noticed [0, ∞] delivery semantics in a widely-used, internal/homegrown message delivery system at a big tech company once. The bug was easy to spot in the source code (which I was looking at for unrelated reasons), but the catch-22 is that engineers with the skills to notice these sorts of subtle but significant infra bugs are the same engineers who would've advised against building (or continuing to use) your own message delivery system in the first place when there are perfectly serviceable open source and SaaS options.

[dan-robertson]

I think whether or not to build your own thing isn’t an obvious choice for a big company. You might have lots of other infrastructure to integrate with and adapting an existing solution might not work as well as making something from scratch that eg integrates with your storage layer or how you manage permissions. The choice may be between having a team dedicated to managing some third party thing (because in the real world these systems have bugs or cases that don’t perform well or need more hardware or rebalancing or whatever) and having a team dedicated to developing and managing an internal solution. The latter case can mean you get to take advantage of existing infrastructure, have less work integrating with this thing, and have in-house experts who can investigate and fix bugs.

I don’t think it’s as simple as always preferring to bring in external things.