Docker Swarm Networking and Dynamic Reverse Proxy

This post will show you how to setup a Swarm Cluster, deploy a couple of microservices, and create a Reverse Proxy Service (with Traefik) in charge of routing requests on their base URLs.

If you haven’t already, create a Swarm cluster, you could use the shell script below to setup a cluster with 3 nodes (1 Manager & 2 Workers)

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#!/bin/sh

for i in 1 2 3; do
  docker-machine create -d virtualbox node-$i
done

eval $(docker-machine env node-1)

docker swarm init --advertise-addr $(docker-machine ip node-1)

TOKEN=$(docker swarm join-token -q worker)

for i in 2 3; do
  eval $(docker-machine env node-$i)
  docker swarm join --token $TOKEN $(docker-machine ip node-1):2377
done

echo "Swarm cluster has been successfuly created !";

eval $(docker-machine env node-1)

docker node ls

Issue the following command to execute the script:

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chmod +x setup.sh
./setup.sh

The output of the above command is as follows:

At this moment, we have 3 nodes:

Our example microservice application consists of two parts. The Books API and the Movies API. For both parts I have prepared images for you that can be pulled from the DockerHub.

The Dockerfiles for both images can be found on my Github.

Create docker-compose.yml file with the following content:

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version: "3.3"

services:
  traefik:
    image: traefik:1.4
    ports:
      - 80:80
      - 8080:8080
    networks:
      - traefik-net
    volumes:
      - /var/run/docker.sock:/var/run/docker.sock
    configs:
      - source: traefik-config
        target: /etc/traefik/traefik.toml
    deploy:
      placement:
        constraints:
          - node.role == manager

  books:
    image: mlabouardy/books-api
    networks:
      - traefik-net
    deploy:
      placement:
        constraints:
          - node.role == worker
      labels:
        - "traefik.port=5000"
        - "traefik.backend=books"
        - "traefik.frontend.rule=Path:/books"

  movies:
    image: mlabouardy/movies-api
    networks:
      - traefik-net
    deploy:
      placement:
        constraints:
          - node.role == worker
      labels:
        - "traefik.port=5000"
        - "traefik.backend=movies"
        - "traefik.frontend.rule=Path:/movies"

networks:
  traefik-net:
    driver: overlay

configs:
  traefik-config:
    file: config.toml

• We use an overlay network named traefik-net, on which we add the services we want to expose to Traefik.
• We use constraints to deploy the APIs on workers & Traefik on Swarm manager.
• Traefik container is configured to listen on port 80 for the standard HTTP traffic, but also exposes port 8080 for a web dashboard.
• The use of docker socket (/var/run/docker.sock) allows Traefik to listen to Docker Daemon events, and reconfigure itself when containers are started/stopped.
• The label traefik.frontend.rule is used by Træfik to determine which container to use for which Request Path.
• The configs part create a configuration file for Traefik from config.toml (it enables the Docker backend)

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logLevel="DEBUG"
debug=true

[web]
address=":8080"

[docker]
endpoint="unix://var/run/docker.sock"
watch=true
swarmmode=true

In order to deploy our stack, we should execute the following command:

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docker stack deploy --compose-file docker-compose.yml api

Let’s check the overlay network:

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docker network ls

Traefik configuration:

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docker config ls

To display the configuration content:

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docker config inspect api_traefik-config --pretty

And finally, to list all the services:

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docker stack ps api

In the list of above, you can see that the 3 containers are being running on node-1, node-2 & node-3 :

If you point your favorite browser (not you IE 😂) to the Traefik Dashboard URL (http://MANAGER_NODE_IP:8080) you should see that the frontends and backends are well defined:

If you check http://MANAGER_NODE_IP/books, you will get a list of books

If you replace the base URL with /movies:

What happens if we want to scale out the books & movies APIs. With the docker service scale command:

We can confirm that:

Obviously Traefik did recognise that we started more containers and made them available to the right frontend automatically:

In the diagram below, you will find that the manager has decied to schedule the new containers on node-2 (3 of them) and node-3 (4 of them) using the Round Robin strategy

Drop your comments, feedback, or suggestions below — or connect with me directly on Twitter @mlabouardy.