feat/endpoint-discovery

[roivaz]

Description

With this PR, the discovery service gains the ability to discover and feed a list of Pod IPs to a subscribed consumer. The endpoints are discovered by watching the EndpointSlices resources in the namespace that match a given label selector.

An endpoint resource would have to be declared like

    - type: endpoint
      generateFromEndpointSlices:
        selector:
          matchLabels:
            kubernetes.io/service-name: test
        clusterName: test
        targetPort: http

This would make the discovery service watch the EndpointSlices generated by the k8s Service named test. Any other custom label selector can be used.

The (debug) logs in the discovery service show how the list of pod IPs is generated and feed to consumers:

2023-05-10T10:41:29Z	DEBUG	setup.xds.cache.v3	respond type.googleapis.com/envoy.config.endpoint.v3.ClusterLoadAssignment[kuard] version "58f6d94cd" with version "57f9787477"
2023-05-10T10:41:29Z	DEBUG	setup.xds.server.v3	Discovery Response	{"TypeURL": "type.googleapis.com/envoy.config.endpoint.v3.ClusterLoadAssignment", "NodeID": "kuard", "StreamID": 1, "Version": "57f9787477", "Resources": ["{\"@type\":\"type.googleapis.com/envoy.config.endpoint.v3.ClusterLoadAssignment\",\"cluster_name\":\"kuard\",\"endpoints\":[{\"lb_endpoints\":[{\"endpoint\":{\"address\":{\"socket_address\":{\"address\":\"10.244.0.14\",\"port_value\":8080}}},\"health_status\":\"HEALTHY\"},{\"endpoint\":{\"address\":{\"socket_address\":{\"address\":\"10.244.0.20\",\"port_value\":8080}}},\"health_status\":\"DRAINING\"}]}]}"], "Pod": "marin3r-envoydeployment-kuard-7578497bb-bbpdn"}

The health status of each endpoint is provided so the consumer can make appropriate load balancing decisions.

/kind feature
/priority important-soon
/assign

This PR depends on #177 being merged first.

How to test

make kind-create
export KUBECONFIG=${PWD}/kubeconfig
kubectl apply -f examples/e2e/deployment

Check the logs of the discovery service and the endpoint pod in the default namespace to see how the list of endpoints is updated each time the number of replicas in the nginx deployment is changed.

[roivaz]

/ok-to-test

[slopezz]

/lgtm

[3scale-robot]

LGTM label has been added.

Git tree hash: 81800917772288d9c3e16de13b4135d015d45522

[slopezz]

/lgtm

[3scale-robot]

LGTM label has been added.

Git tree hash: c10f7633594ff2bf58d1b7bbe2054d47596dd632

[roivaz]

/approve

[3scale-robot]

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