alt Hacker News> This is a straightforward error in the code, which had existed undetected for many years. This type of code error is prevented by languages with strong type systems. In our replacement for this code in our new FL2 proxy, which is written in Rust, the error did not occur.
Cloudflare deployed code that was literally never tested, not even once, neither manually nor by unit test, otherwise the straightforward error would have been detected immediately, and their implied solution seems to be not testing their code when written, or even adding 100% code coverage after the fact, but rather relying on a programming language to bail them out and cover up their failure to test.
Large scale infrastructure changes are often by nature completely untestable. The system is too large, there are too many moving parts to replicate with any kind of sane testing, so often, you do find out in prod, which is why robust and fast rollback procedures are usually desirable and implemented.