Everything you ever wanted to know about UDP sockets but were afraid to ask, part 1

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Snippet from internal presentation about UDP inner workings in Spectrum. Who said UDP is simple!

Historically Cloudflare’s core competency was operating an HTTP reverse proxy. We’ve spent significant effort optimizing traditional HTTP/1.1 and HTTP/2 servers running on top of TCP. Recently though, we started operating big scale stateful UDP services.

Stateful UDP gains popularity for a number of reasons:

QUIC is a new transport protocol based on UDP, it powers HTTP/3. We see the adoption accelerating.

We operate WARP — our Wireguard protocol based tunneling service — which uses UDP under the hood.

— We have a lot of generic UDP traffic going through our Spectrum service.

Although UDP is simple in principle, there is a lot of domain knowledge needed to run things at scale. In this blog post we’ll cover the basics: all you need to know about UDP servers to get started.

Connected vs unconnected

How do you “accept” connections on a UDP server? If you are using unconnected sockets, you generally don’t.

But let’s start with the basics.

Read the article