Adopt Envoy in place of HAProxy for load balancing

[shwetha-s-poojary]

Switching load balancing from HAProxy to Envoy.
Based on the discussion in the referenced Slack thread: https://kubernetes.slack.com/archives/CEKK1KTN2/p1759769331878379.

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[stmcginnis]

Others, please correct me if I am wrong, but I don't believe we want to explicitly call docker commands here. User may be using podman or nerdctl and not have docker present on their system. Is there an equivalent to sending HUP to envoy?

[aojea]

you do not need to restart , see how is done in cloud provider kind https://github.com/kubernetes-sigs/cloud-provider-kind/blob/4820e03979d5ff7fbcd8645794db2ff39a608b3f/pkg/loadbalancer/proxy.go#L276-L313

[BenTheElder]

Yeah, we should not exec directly to docker in particular here, but we also don't need to.

[shwetha-s-poojary]

@stmcginnis envoy does support hot restarts, but for this scenario a simple container restart seems to be the most reliable and straightforward option. I’ll look into detecting the container runtime so we can use the appropriate tool instead of assuming docker.
@aojea @BenTheElder from my understanding, only dynamic (xDS) configuration avoids restarts; static configuration still requires one. For the kind use case, static config seems sufficient and avoids the complexity of a full dynamic config setup. The cloud-provider-kind example you shared above uses dynamic config, but I believe the earlier version relied on static config and required restarts (ref: PR link).
Please correct me if I’m mistaken anywhere — I appreciate the guidance.

[aojea]

@shwetha-s-poojary if we know all the configuration before hand you just need to pass the final config during the entrypoint and you can just use existing libraries to create the container, see

https://github.com/kubernetes-sigs/cloud-provider-kind/blob/dc1a6e4c3b21716be9f87476d5cdb78389f05537/pkg/loadbalancer/server.go#L247-L263

the example I provided in my previous comment is to update the configuration dynamically without having to restart the container, you can write files on the filesystem of the container and envoy will pick the config and autoconfigure itself, no need to restarts

[BenTheElder]

I’ll look into detecting the container runtime so we can use the appropriate tool instead of assuming docker.

I'd really rather not expand the node container runtime abstraction just for this purpose, haproxy has been working ~fine.

But see antonio's comment above.

[aojea]

@shwetha-s-poojary so you need to follow the cloud-provider-kind implementation, a straw man approach will be

1. bootstrap the container with an initial config that allow to use dynamic configuration based on files

• example config
  https://github.com/kubernetes-sigs/cloud-provider-kind/blob/4820e03979d5ff7fbcd8645794db2ff39a608b3f/pkg/loadbalancer/proxy.go#L33-L53

• override the config during container start https://github.com/kubernetes-sigs/cloud-provider-kind/blob/37c196059f9c31de6f0734e22b608923f00eb195/pkg/loadbalancer/server.go#L247-L257

unfortunately I think this is per provider https://github.com/search?q=repo%3Akubernetes-sigs%2Fkind%20runArgsForLoadBalancer&type=code

2. at runtime, add the expected configuration

create the config as in cloudprovider kind

https://github.com/kubernetes-sigs/cloud-provider-kind/blob/4820e03979d5ff7fbcd8645794db2ff39a608b3f/pkg/loadbalancer/proxy.go#L82-L273

and write it to the corresponding node in the expected path (configured in step 1)

kind/pkg/cluster/internal/create/actions/loadbalancer/loadbalancer.go

Lines 77 to 91 in 02382a0

	// create loadbalancer config data
	loadbalancerConfig, err := loadbalancer.Config(&loadbalancer.ConfigData{
	ControlPlanePort: common.APIServerInternalPort,
	BackendServers: backendServers,
	IPv6: ctx.Config.Networking.IPFamily == config.IPv6Family,
	})
	if err != nil {
	return errors.Wrap(err, "failed to generate loadbalancer config data")
	}
	// create loadbalancer config on the node
	if err := nodeutils.WriteFile(loadBalancerNode, loadbalancer.ConfigPath, loadbalancerConfig); err != nil {
	// TODO: logging here
	return errors.Wrap(err, "failed to copy loadbalancer config to node")
	}

[shwetha-s-poojary]

@aojea @BenTheElder @stmcginnis Thanks for the guidance! Looks like switching to dynamic config is the way to go.I'll get on it.