kpng-diffstore

Anyone building a kube proxy impl needs to diff endpoints/services periodically.

• When an endpoint is created, you need to updated LB rules to Loadbalkance to that endpoint
• When an endpoint is deleted, you need to delete a LB endpoint
• When a service is created, you need to add forwarding rule to a node to not reject that IP:port combination (and also add endpoints in the bullets above, likely)

... and so on.

So you need to know:

• when things were added (so you can update things)
• what changed (so you can avoid rewriting already current forwarding rules on the node)

KPNG has built an abstract tool for this called DIFFSTORE lets learn about it.

DiffStore is a powerful tool provided by KPNG sigs.k8s.io/kpng/diffstore for tracking incremental changes and computing deltas after processing a full state.

Defining diff-store

// loadBalancerStore
var loadBalancerStore = diffstore.NewAnyStore[string, *hcn.LoadBalancer](func(a, b *hcn.LoadBalancer) bool {
    return a.Equal(b)
})

Adding items to diff-store

loadBalancerStore.Get(loadBalancer.Key()).Set(loadBalancer)

Computing incremental changes

# Done() computes all the incremental changes internally
loadBalancerStore.Done()

# Reset() resets the diffstore for next fullstate
loadBalancerStore.Reset()

Iterating over incremental changes

for _, item := range loadBalancerStore.Deleted() {
    loadBalancer := item.Value().Get()
    // delete existing loadbalancer
}

for _, item := range loadBalancerStore.Changed() {
    loadBalancer := item.Value().Get()
    if item.Created() {
        // create new loadBalancer
    }else{
        // update existing loadBalancer
    }
}