Kubernetes API, RDS example

Small golang binary watching Istio Gateway resources on Kubernetes API and serving them as Envoy RDS configuration

Introduction

This project is a proof of concept demonstrating how to dynamically control an Envoy Proxy based on Istio Gateway resources on Kubernetes API.

It consists of one binary watching Kubernetes API for Istio Gateway resources. If these resources are annotated with custom annotations (more details below), they are served by the binary as RDS configuration (Envoy Route Discovery Service). This configuration is then consumed by Envoy to dynamically route traffic.

Example of annotations

# Annotations will be interpreted as "create a Route matching * & hello.example.org hostname, /hello prefix to cluster some_service"
apiVersion: networking.istio.io/v1alpha3
kind: Gateway
metadata:
  name: commongateway
  annotations:
    stoakes.github.com/cluster: some_service
    stoakes.github.com/hostname: "*,hello.example.org"
    stoakes.github.com/prefix: "/hello"
spec:
  selector:
    app: envoy
  servers:
    - port:
        number: 8000
        name: http
        protocol: HTTP
      hosts:
        - "*"

Resulting RDS configuration

{
    "@type":"type.googleapis.com/envoy.admin.v3.RoutesConfigDump",
 "dynamic_route_configs":[
    {"version_info":"0",
     "route_config":{
        "@type":"type.googleapis.com/envoy.api.v2.RouteConfiguration",
        "name":"rds_config_name",
        "virtual_hosts":[
            {"name":"commongateway-default","domains":["*","hello.example.org"],"routes":[{"match":{"prefix":"/hello"},"route":{"cluster":"some_service"}}]}
        ]
        },
     "last_updated":"2020-09-29T07:06:34.357Z"}
     ]
}

Getting started

Build & Start Golang binary

go build -o k8s-watcher-rds-server
# Assuming you have a valid kubeconfig locally
./k8s-watcher-rds-server watch
# or use a specific ./k8s-watcher-rds-server watch -c /etc/rancher/k3s/k3s.yaml 

Start Envoy listening to watcher for RDS configuration

RDS stands for Route Discovery Service.

docker run --rm --net=host \
            -v $(pwd)/deploy/envoy-config-rds.yaml:/etc/front-envoy.yaml \
            envoyproxy/envoy:v1.15.0 /usr/local/bin/envoy \
                     -c /etc/front-envoy.yaml \
                     --service-cluster front-proxy \
                     --service-node router~172.17.42.42~front-proxy.ns~ns.svc.cluster.local \
                     -l debug

Deploy Istio Gateway CRD & a basic gateway on your cluster

kubectl apply -f https://raw.githubusercontent.com/Stoakes/k8s-watcher-rds-server/master/deploy/istio.yaml

Once deployed, you can now browse to http://localhost:8001/config_dump and check Envoy configuration, you should see a route on hello.example.org

You can also run curl http://localhost:8000/ and get Envoy admin HTML (normally exposed on port 8001).