Multiple services are not spread with L2

[nvlan]

Is your feature request related to a problem?

When I create multiple services that have the same endpoint, metallb does some hashing of nodeName + serviceIP and uses this to pick which node should win the election and announce a given IP.
However, I found that most times metallb end up choosing the same node to announce more than one IP: in a cluster with 7 nodes and 3 ingress loadbalancers, the same node hosts two IPs while the remaining IP is scheduled to a different node.

Describe the solution you'd like

In the hopes to avoid most traffic using a single node, the election algorithm should be random enough to pick different nodes for different services: in my setup I use ingress-nginx and create three services that all have the same endpoint, only each service has its own contiguous IP.
I was wondering if it would make sense to use the stable version of sort.Slice in here: https://github.com/fedepaol/metallb/blob/3df9cbd68b9d24edeaba6d84f30fcf3b446a7289/speaker/layer2_controller.go#L116-L126 since it is the only explanation I could thing of for this behavior.

Additional context

No response

I've read and agree with the following

• I've checked all open and closed issues and my request is not there.
• I've checked all open and closed pull requests and my request is not there.

[fedepaol]

I am not sure using a stable sort would help here (if I got your suggestion right), as the keys are different by construction (same ip, different node name, hashed).
Changing the behaviour to something more even would introduce a state that we currently don't want to introduce.

I can try do do a few simulations to see if we are missing something obvious with the current logic, or if you were just not lucky.

[nvlan]

That was my suggestion, yes. I had three separate L2 advertisements each for a pool with a single IP, and I used a nodeSelector label to pin said IPs to nodes 1-3. After an outage (labels were not reapplied after the three first nodes were rebuilt), I simply added a single pool with three IPs and a single L2 advertisement that uses all nodes. When I deployed this new config to 5 different clusters, I see a curious pattern: first IP is assigned to the third node, second and third are assigned to the last node (each cluster has between 3 and 9 nodes, names are worker[10-19]-domain).
Please let me know if you need any further info, thanks!