real-time analytics, what's your go-to architecture

I'm working on this project, and we need to show real-time user activity metrics on a dashboard. We're expecting potentially thousands of users at the same time, plus a constant flow of events. I've seen a couple of approaches, like using Kafka with Spark Streaming, or maybe something a bit more straightforward with Redis pub/sub and a backend service. I'm wondering what has worked well for others and if there are any traps to watch out for when building for scale and low latency. So, what's your go-to setup for this?