I’m doing some self-education these days, and was exploring YARP today. I learned about this via HackerNews some time ago, and only now got around to taking the time to explore in more detail. As Microsoft describes it, YARP is “a library to help create reverse proxy servers that are high-performance, production-ready, and highly customizable.”

It’s not a reverse proxy in its own right, but a library that you can embed into an ASPNET app to allow it to act as a reverse proxy. The “Yet Another” moniker is completely appropriate; there are many, many Reverse Proxies out there in various shapes, sizes and configurations. Why Microsoft wanted to build another one when there are good options out there – Envoy, nginx, haproxy, and many others – is perhaps a topic worth exploring (Google, my most recent employer, promotes the open-source Envoy proxy as a general-purpose RP, and also sells an API Platform, Apigee, that includes its own reverse proxy). It seems to me that Microsoft has large cloud investments, and wants to have control over this particular critical piece of widely-used infrastructure. Rather than compromise with something that’s already out there, go build something that fits the requirements for their massive cloud footprint, as well as for the shops other than Microsoft who are invested in .NET. I don’t think it’s worthy of too much more discussion than that.

With so many available options in reverse proxies, an interested observer might want to have some insight into comparisons between them. Now there are various criteria a person might want to investigate when comparing – features like hot-reload of configuration, the configuration model in general, support for “farms” of proxies all centrally managed, platform availability, performance…. Any reader could probably add two or three more items to that list.

All of that is interesting, but I don’t have time to conduct a thorough comparison at this time. But I will offer one quick observation. While exploring Envoy proxy back in November, I built it from source on my macbook pro. The build was a bear, and took maybe 90 minutes? Something like that. Basically it built every library that the envoy proxy depended on. I suspect most people don’t do that; they just use the docker container that the envoy project publishes.

Just for fun I cloned the yarp repo and ran a build. After sorting out some puzzles [1, 2] on my own, the build completed in about 55 seconds. That’s a pleasant surprise.

I know that with Bazel, the envoy build will be much faster on subsequent runs. But even so, building a YARP proxy is much much faster than building Envoy.