WebSockets are now a standard JavaScript Web API and there are Node packages like ws or C++ and Rust implementations such as uWebSockets and tungstenite. These are great if you have the infrastructure already or have time. If you want quickly to build out a proof-of-concept or, even, if you anticipate unpredictable load, then serverless is well worth a look. Ably, together with alternatives like partykit can help you get going quickly, if you do pick the serverless route.