Hello all, I have migrated another production web service over to Nim and wanted to share how it turned out. I hope some of you may find this interesting.
#### The Migration The service I migrated to Nim manages around 100k concurrent mostly long-lived WebSocket connections. These WebSocket connections are opened by client apps (Android, Windows desktop, etc) and are used to receive realtime events. I wrote the new WebSocket server using [Mummy](https://github.com/guzba/mummy), [Ready](https://github.com/guzba/ready) and [JSONy](https://github.com/treeform/jsony). I wasn't quite sure what to expect for performance but have been pleasantly surprised. The new Nim server has now been running for a week now on a single 2 vCPU + 16GB RAM VM. This VM is behind a load balancer for HTTPS termination, the same kind of setup as described in [my previous post](https://forum.nim-lang.org/t/9902). With 100k open WebSocket connections, the new server's CPU and RAM usage are both under 10% (~7.5%ish). This is pretty great. While I don't have 1 million production WebSocket connections to prove it, this provides a solid indication that Nim + Mummy can handle 1M+ WebSocket connections on a single small VM which is quite cool. The server is also not just sitting there idle either, every minute over 200k messages are sent to clients (most of these are simple heartbeat messages). Considering this new Nim server has been humming along without any issues for the past week I am ready to say the migration has been a success. #### Thoughts I have now put Nim and Mummy into production serving both [a lot of HTTP request traffic](https://forum.nim-lang.org/t/9902) and a lot of WebSocket connections. Since everything has performed really well in both cases it is pretty easy to say I am happy with the results I have achieved with Nim. Why does this matter to you? 1. Many other languages used for web programming are either not capable of handing so many WebSocket connections per VM or have to go to extraordinary effort to make it work. This out-of-the-box performance highlights a strength of Nim. 2. If you're learning Nim (or interested in doing so), this provides real-world evidence that Nim is capable of exceptional performance for web servers too, not just in games or systems programming. Seems smart to me to learn a language that can do so much while still having such pleasant syntax. 3. [Nim 2.0](https://forum.nim-lang.org/t/10051) is very close and for me the highlight is ARC/ORC + threads:on as the new defaults. Well, everything written above is multi-threaded and compilied with those settings. Having these servers running in production for days, weeks and soon months without issue provides more proof that Nim's threading capabilities are very real, solid and perhaps under-utilized. 4. It can be hard to know if a programming language or web server or lib or whatever is a good choice without real-world testimonials of things actually working in production. A demo app and passing some tests are not always enough to go on. Does the system last in front of a lot of traffic for months on end? That's a very high bar to clear and what I want to prove. Thanks for giving this a read and good luck with your own Nim adventures.
