Image Credits: Unsplash Denys Nevozhai

Envoy as Edge Proxy over Kubernetes

What is Envoy?

Envoy is an open source, modern and high performance proxy. It was designed for cloud native applications and for large microservice “service mesh” architectures.

In the world of envoy, the backend is called upstream and the front-end (or client) is called downstream. However, to keep things simple we’ll not use these terms in this blog.

Lets deploy

Don’t worry , I’ll keep it simple!

Deploy Environment

To simulate a kubernetes cluster we’ll use Docker Desktop with minikube:

minikube start --nodes 3 --name my-minikube-cluster

Above command will create a cluster in minikube with 3 nodes.

Backend Environment

For simulating a backend environment, we’re using 2 simple nginx deployments with services listening on port 81 and port 82 respectively. All the resources of the backend will be in namespace named “nginx-app-namespace”.

nginx-app-1.yaml

---
apiVersion: v1
kind: Namespace
metadata:
  name: nginx-app-namespace
---
apiVersion: v1
kind: ConfigMap
metadata:
  name: nginx-app-config-1
  namespace: nginx-app-namespace
data:
  index.html: |
    App-1: Hello, I'm Ankit Kumar!
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-app-deployment-1
  namespace: nginx-app-namespace
spec:
  # replicas: 2
  selector:
    matchLabels:
      app: nginx-app-pod-label-1
  template:
    metadata:
      labels:
        app: nginx-app-pod-label-1
    spec:
      containers:
        - name: nginx-app-container-1
          image: nginx:latest
          ports:
            - containerPort: 80
          lifecycle:
            preStop:
              exec:
                command: ["/usr/sbin/nginx", "-s", "quit"]
          volumeMounts:
            - name: nginx-webpage-volume-1
              mountPath: /usr/share/nginx/html
          resources:
            requests:
              memory: "150Mi"
              cpu: "250m"
            limits:
              memory: "250Mi"
              cpu: "500m"
      volumes:
      - name: nginx-webpage-volume-1
        configMap:
          name: nginx-app-config-1
---
apiVersion: v1
kind: Service
metadata:
  name: nginx-app-service-1
  namespace: nginx-app-namespace
spec:
  selector:
    app: nginx-app-pod-label-1
  ports:
    - protocol: TCP
      port: 81
      targetPort: 80
  type: ClusterIP

nginx-app-2.yaml

---
apiVersion: v1
kind: Namespace
metadata:
  name: nginx-app-namespace
---
apiVersion: v1
kind: ConfigMap
metadata:
  name: nginx-app-config-2
  namespace: nginx-app-namespace
data:
  index.html: |
    App-2: Hello, what's your good name?
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-app-deployment-2
  namespace: nginx-app-namespace
spec:
  # replicas: 3
  selector:
    matchLabels:
      app: nginx-app-pod-label-2
  template:
    metadata:
      labels:
        app: nginx-app-pod-label-2
    spec:
      containers:
        - name: nginx-app-container-2
          image: nginx:latest
          ports:
            - containerPort: 80
          lifecycle:
            preStop:
              exec:
                command: ["/usr/sbin/nginx", "-s", "quit"]
          volumeMounts:
            - name: nginx-webpage-volume-2
              mountPath: /usr/share/nginx/html
          resources:
            requests:
              memory: "150Mi"
              cpu: "250m"
            limits:
              memory: "250Mi"
              cpu: "500m"
      volumes:
      - name: nginx-webpage-volume-2
        configMap:
          name: nginx-app-config-2
---
apiVersion: v1
kind: Service
metadata:
  name: nginx-app-service-2
  namespace: nginx-app-namespace
spec:
  selector:
    app: nginx-app-pod-label-2
  ports:
    - protocol: TCP
      port: 82
      targetPort: 80
  type: ClusterIP

Deploy above applications:

kubectl apply -f ./nginx-app-1.yaml -f nginx-app-2.yaml

kubectl get pods -n nginx-app-namespace

Deploying Envoy as a Layer 7 HTTP proxy over Kubernetes

Envoy will route and load balance traffic to the backend nginx deployments.

Note: We are currently using version 1.28.x, the latest stable release at the time of writing this blog.

envoy-deployment.yaml

---
apiVersion: v1
kind: Namespace
metadata:
  name: envoy
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: myapp
  namespace: envoy
spec:
  replicas: 1
  selector:
    matchLabels:
      app: myapp
  template:
    metadata:
      labels:
        app: myapp
    spec:
      containers:
        - name: envoy
          image: envoyproxy/envoy:v1.28-latest
          ports:
            - containerPort: 9000
          volumeMounts:
            - name: envoy-config
              mountPath: /etc/envoy
      volumes:
        - name: envoy-config
          configMap:
            name: envoy-configmap
---
apiVersion: v1
kind: ConfigMap
metadata:
  name: envoy-configmap
  namespace: envoy
data:
  envoy.yaml: |
    static_resources:
      listeners:
        - address:
            socket_address:
              address: 0.0.0.0
              port_value: 9000
          filter_chains:
            - filters:
                - name: envoy.filters.network.http_connection_manager
                  typed_config: 
                    "@type" : type.googleapis.com/envoy.extensions.filters.network.http_connection_manager.v3.HttpConnectionManager
                    stat_prefix: http_proxy
                    route_config:
                      name: all
                      virtual_hosts:
                        - name: all_backend_cluster
                          domains:
                            - '*'
                          routes:
                            - match: { prefix: "/app1" }
                              route:
                                cluster: app1_backend_cluster
                                prefix_rewrite: "/"
                            - match: { prefix: "/app2" }
                              route:
                                cluster: app2_backend_cluster
                                prefix_rewrite: "/"
                            - match: { prefix: "/" }
                              route:
                                cluster: all_backend_cluster
                                prefix_rewrite: "/"
                    http_filters:
                      - name: envoy.filters.http.router
                        typed_config:
                          "@type": type.googleapis.com/envoy.extensions.filters.http.router.v3.Router
      clusters:
        - name: all_backend_cluster
          connect_timeout: 1s
          type: strict_dns
          lb_policy: ROUND_ROBIN
          load_assignment:
            cluster_name: all_backend_cluster
            endpoints:
              - lb_endpoints:
                  - endpoint:
                      address:
                        socket_address:
                          address: nginx-app-service-1.nginx-app-namespace.svc.cluster.local
                          port_value: 81
                  - endpoint:
                      address:
                        socket_address:
                          address: nginx-app-service-2.nginx-app-namespace.svc.cluster.local
                          port_value: 82
        - name: app1_backend_cluster
          connect_timeout: 1s
          type: strict_dns
          lb_policy: ROUND_ROBIN
          load_assignment:
            cluster_name: app1_backend_cluster
            endpoints:
              - lb_endpoints:
                  - endpoint:
                      address:
                        socket_address:
                          address: nginx-app-service-1.nginx-app-namespace.svc.cluster.local
                          port_value: 81
        - name: app2_backend_cluster
          connect_timeout: 1s
          type: strict_dns
          lb_policy: ROUND_ROBIN
          load_assignment:
            cluster_name: app2_backend_cluster
            endpoints:
              - lb_endpoints:
                  - endpoint:
                      address:
                        socket_address:
                          address: nginx-app-service-2.nginx-app-namespace.svc.cluster.local
                          port_value: 82

Let’s take some time to understand the configuration in `envoy.yaml`. An envoy configuration file has two main components i.e.:

1. Listeners
2. Clusters

Both are defined under static_resources block.

1. Listeners

Its where we define where and how envoy is to accept and filter/process the incoming traffic.

In layman’s terms, its where the envoy receives the incoming traffic from the front-end.

Some of the configuration that we do here is:

“address” block

Socket address
The address and port where envoy is exposed to and receives traffic from the front-end.

“filters” block

Filters
They allow us to customize and manipulate the behavior of the proxy for specific types of traffic. Envoy has various builtin filters. Here we’re using one such filter for HTTP traffic. For other filters, you may check here.

Depending on the filter you’re using, there are a set of configurable parameters. In our case of HTTP filter, we’re using such parameters to configure the routing behavior to specific backend, based on path, by reading and modifying the header of incoming traffic.

In our configuration, if the traffic is coming at “/” then it’ll be routed to “all_backend_cluster” and if its coming to “/app1” then it’ll be routed to “app1_backend_cluster” and similarly for “/app2”.

Note: The filter route rules is checked/applied in order its written i.e. the rule which is written first is checked or applied first.

2. Clusters

Cluster is where we define the backend and how the traffic is distributed among them.

“all_backend_cluster” block

Some important things that we configure here are:

Connection Timeout
The maximum allowed time for Envoy to try establish a connection to the backend. If connection is not established withing this time frame, Envoy considers it as failure.

Type
The value of this field determines how Envoy discovers and manages backend hosts. In our case, we’re using strict_dns which means Envoy resolves DNS entries provided in the endpoint to IP addresses and uses them to connect to the backend host.

Load Balancing Policy
Specifies the load balancing policy for distributing traffic among upstream hosts. There are many load balancing policies provided by envoy. In our case, we’re using the standard Round-Robin.

Endpoints
It’s where we define the backend host endpoints i.e. their address and port on which they are exposed. In our case, since envoy is in the same cluster we use <service-name>.<namespace-name>.svc.cluster.local in address to point to the service of the nginx deployments.

In our config file, we have configured 3 clusters:

1. all_backend_cluster
   Here we have configured 2 backend endpoints i.e both the service of the 2 nginx deployments. So, traffic from any routing rule using this cluster as backend will be load balanced between the 2 services of the nginx deployments.
2. app1_backend_cluster
   Here we have only 1 backend endpoint i.e. the service of nginx-app-2. So, traffic from any routing rule using this cluster as backend will always be routed to nginx-app-1.
3. app2_backend_cluster
   Similar to app1_backend_cluster, here all the traffic will always be routed to nginx-app-2.

To deploy envoy use:

kubectl apply -f ./envoy-deployment.yaml

The envoy pod is configured (by above config-map) to listen on port 9000. Once the envoy pod is ready you can check by binding it with a local port:

kubectl port-forward -n envoy po/<your-envoy-port-name> 9000:9000

Note: Be sure to add your pod name to above command.

Or you can directly use:

kubectl port-forward -n envoy po/$(k get po --no-headers -n envoy | awk '{ print $1 }') 9000:9000

Now if you open:

http://localhost:9000

in your browser, you should see below content:

Envoy routing traffic to nginx-app-deployment-1

and if you refresh, you should see the content of the second nginx backend:

Envoy routing traffic to nginx-app-deployment-2

If you open:

http://localhost:9000/app1

you’ll always land to app-1:

Envoy routing traffic to nginx-app-deployment-1

and similarly for http://localhost:9000/app2 you’ll always land to app-2.

This was a pretty basic configuration of envoy, feel free to explore more powerful features of envoy (link to envoy’s official documentation).

I hope it helped, if yes please give it a like and share this blog among your geek friends.

Thank You!
See you soon!