Routing with the Envoy proxy in under 10 minutes

Running the App with Envoy as an Edge Proxy

Clone the repository and checkout to the envoy branch by executing the command below:

git clone https://github.com/rinormaloku/k8s-mastery.git \
    && cd k8s-mastery/ \
    && git checkout envoy

Now build the images and run the containers by executing the command below from the k8s-mastery directory:

docker-compose --compatibility up --build

Check that the application is up and running in http://localhost/. It is! That was quick and simple. Let’s get a quick overview of how this works

Envoy Edge Proxy an Overview

The Sentiment Analysis application is composed of three external facing services:

• SA-Frontend is routed to on three cases:
  1. Base path: /
  2. Static files: /static
  3. Images Files: .png, .ico etc.
• SA-WebApp is routed to when the request path is /sentiment.
• SA-Feedback is routed to when the request path is /feedback.

To be able to target the clusters the envoy needs an address, this is dependent on the environment, and in our case, we are using Docker Compose which creates an entry for every service, in other words with the following config in docker-compose.yaml:

  sa-frontend:
    build: 
      context: ./sa-frontend
    image: rinormaloku/sentiment-analysis-frontend:feedback
    networks:
      - envoymesh
    expose:
      - "80"

This way the other services in the network can access sa-frontend using its name sa-frontend. Which is used in the envoy configuration in the next section.

Envoy Static Configuration

In Envoy nomenclature services are called clusters (i.e. there can be more than one service in the cluster), and below we display the configuration for sa-frontend cluster to forward requests to the address sa-frontend, defined in the file external-envoy.yaml:

  clusters:
  - name: sa-frontend
    connect_timeout: 0.25s
    type: strict_dns
    lb_policy: round_robin
    http_protocol_options: {}
    hosts:
    - socket_address:
        address: sa-frontend
        port_value: 80

With the cluster defined we need to route to them, which is specified in the filters section for the listener on port 0.0.0.0:80, as shown below:

- match:
    path: "/"
  route:
    cluster: sa-frontend
- match:
    prefix: "/static"
  route:
    cluster: sa-frontend
- match:
    regex: '^.*\.(ico|png|jpg)$'
  route:
    cluster: sa-frontend

And this is it! With this simple config we are:
1. Listening for requests from the downstream (can be any client in our case it’s the browser) in port 80.
2. In case of matching any of the options, we are forwarding the requests to the upstream, i.e instances of sa-frontend cluster.
3. Docker compose has added a DNS entry that forwards requests of sa-frontend to its container.

Summary

In this article, in under 10 minutes, we got the microservice application up and running and we got introduced to the most important Envoy Proxy concepts:

• Downstream,
• Upstream,
• Listeners,
• Clusters,
• Static Configuration

If you like quick and to the point articles like this one, let me know! 🙂