What are the limitations of ServiceLB compared to MetalLB/kube-vip?

[barrettc]

I'm in the process of building a bare-metal k3s cluster and I'm trying to understand the differences around when I would need to use something like MetalLB instead of the built-in ServiceLB. For use case context, my cluster will be primarily receiving sensor readings via MQTT via VerneMQ.

Most searches I've found are people using MetalLB and even the k3s documentation has the following note:

For exposing LoadBalancer Services, external load-balancers can be used alongside or instead of ServiceLB, but in most cases, replacement load-balancer controllers such as MetalLB or Kube-VIP are a better choice.

The majority of hits on ServiceLB are inquiries on how to disable it.

I'm just having trouble finding the exact reasons why MetalLB is recommended. What are the limitations with ServiceLB?

[brandond]

ServiceLB does not give you a real load-balanced VIP. As described in the documentation, it just exposes the service on node addresses, and set those node addresses as the loadbalancer addresses.

If you want a REAL load-balanced address, you need something else.