Julia EvansJun 19, 2024

when I asked people to explain how UDP works I got a lot of answers to the effect of "it's spray and pray"

but I'm having trouble thinking of examples of UDP-based protocols that actually work in a "spray and pray" way —

* DNS is "send 1 packet, retry if you don't get a reply”
* QUIC is a sophisticated system for streaming data over UDP
* I'd guess that video protocols correct for packet loss
* maybe statsd is a "spray and pray” system?

(please do not reply to this explaining how UDP works)

Show threadÉcole des Bro-ArtsJun 19, 2024
@b0rk I think you're on the right track here. Statsd is a great example--and as I'm sure you remember, that can make your graphs wrong. There's also the Consul UDP gossip layer--remember when that DDOSed itself? 🤣
Show threadJulia EvansJun 19, 2024
@aphyr I don't remember that Consul issue actually, I'll look it up! thanks for the pointer
Show threadÉcole des Bro-Arts
@b0rk I don't know if we ever did a writeup on that one--I have this possibly mistaken memory that it was something like load + packet loss + an aggressive retry mechanism which caused a storm in the gossip layer. Might have been some kind of nack/flow control message issue too? OTOH Nelson's slides (https://www.slideshare.net/slideshow/operating-consul-as-an-early-adopter/53333600) point to churn in service watches. That might *also* be a flow control issue... @coda, you remember this one?
Operating Consul as an Early Adopter

Operating Consul as an Early Adopter - Download as a PDF or view online for free

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Jun 19, 2024 at 1:51pmWeb
Show threadCodaJun 19, 2024
@aphyr @b0rk I don’t remember any details, just that consul 0.1 was a rodeo.