how to manage message queue scaling with fluctuating loads?

hey everyone, i'm putting together a new system, and we'll be using message queues a lot for different services to talk to each other. the tricky part is, our workload isn't steady, it really jumps around a lot during the day and week. i'm trying to figure out the smartest way to scale our message queue setup, you know, like Kafka or RabbitMQ, so we don't get slammed during busy periods and don't spend too much when things are quiet. what have you guys found works well for auto-scaling message queues? like, based on how many messages are waiting or how fast they're being sent. any particular settings or ways to keep an eye on things you'd suggest