Using Traefik in Docker as a Reverse Proxy for Docker Containers

Docker containers allow for quick and easy deployment of services and applications. However, as the number of deployed applications grows, and when multiple instances of a single service are required (especially relevant for microservices architecture), we must distribute network traffic. For this purpose, you can use Traefik, a modern open-source reverse proxy server designed specifically to work with Docker containers. In this guide, we will configure Traefik as a reverse proxy for several applications running in Docker containers.

Prerequisites

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To use Traefik, the following are required:

• A cloud server or a virtual machine with any pre-installed Linux distribution. We will be using Ubuntu 22.04.

• Docker and Docker Compose installed. See our installation guide. 

In this guide, we will use two containers with the Nginx web server. Each container will display a specific message when accessed by its domain name. We will cover the creation of these containers further below.

Configuring Traefik

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Let's start by setting up Traefik:

1. Create a directory for storing configuration files and navigate into it:

mkdir ~/test-traefik && cd ~/test-traefik

2. Inside the project’s root directory, create three subdirectories: one for the Traefik configuration file and two others for the configuration files of the applications that will use Traefik:

mkdir traefik app1 app2

3. Create the main configuration file for Traefik named traefik.yml in the previously created traefik directory:

nano traefik/traefik.yml

Insert the following code into the file:

entryPoints:
  web:
    address: ":80"

providers:
  docker:
    exposedByDefault: false

api:
  dashboard: true
  insecure: true

Let’s look closer at the parameters.

• entryPoints define the ports and protocols through which Traefik will accept requests. They specify on which port and IP address the service will listen for traffic.

  • web — A unique name for the entry point, which can be referenced in routes. In this example, we use the name web.

  • address: ":80" — Indicates that the entry point will listen for traffic on port 80 (HTTP) across all available network interfaces on the system.

• providers specify the sources of information about which routes and services should be used (e.g., Docker, Kubernetes, files, etc.).

  • docker — Enables and uses the Docker provider. When using the Docker provider, Traefik automatically detects running containers and routes traffic to them.

  • exposedByDefault: false — Disables automatic exposure of all Docker containers as services. This makes the configuration more secure: only containers explicitly enabled through labels (traefik.enable=true) will be routed (i.e., will accept and handle traffic).

• The api section contains settings for the administrative API and Traefik's built-in monitoring web interface.

  • dashboard: true — Enables Traefik's web-based monitoring dashboard, which allows you to track active routes, entry points, and services. The dashboard is not a mandatory component and can be disabled by setting this to false.

  • insecure: true — Allows access to the monitoring dashboard over HTTP. This is convenient for testing and getting familiar with the system but is unsafe to use in a production environment. To ensure secure access to the dashboard via HTTPS, set this to false.

Preparing Configuration Files for Applications

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Now, let's prepare the configuration files for the applications that will use Traefik as a reverse proxy. We will deploy two Nginx containers, each displaying a specific message when accessed via its address.

1. Create the Nginx configuration file for the first application:

nano app1/default.conf

Contents:

server {
    listen 80;
    server_name app1.test.com;

    location / {
        root /usr/share/nginx/html;
        index index.html;
    }
}

For the server name, we specify the local domain app1.test.com. You can use either an IP address or a domain name. If you don't have a global domain name, you can use any name that is accessible only at the local level. Additionally, you will need to add the chosen domain to the /etc/hosts file (explained later).

Next, create the html directory where the index.html file for the first application will be stored:

mkdir app1/html

Write the message "Welcome to App 1" into the index.html file using input redirection:

echo "<h1>Welcome to App 1</h1>" > app1/html/index.html

2. Repeat the same steps for the second application, but use values specific to the second app:

nano app2/default.conf

Contents:

server {
    listen 80;
    server_name app2.test.com;

    location / {
        root /usr/share/nginx/html;
        index index.html;
    }
}

Set the local domain name for the second application as app2.test.com.

Create the html directory for the second application:

mkdir app2/html

Write the message "Welcome to App 2" into the index.html file:

echo "<h1>Welcome to App 2</h1>" > app2/html/index.html

3. Since we used local domain names, they need to be registered in the system. To do this, open the hosts file using any text editor:

nano /etc/hosts

Add the following entries:

127.0.0.1 app1.test.com  
127.0.0.1 app2.test.com  

The final project structure should look like this:

test-traefik/  
├── app1/  
│   ├── default.conf  
│   └── html/  
│       └── index.html  
├── app2/  
│   ├── default.conf  
│   └── html/  
│       └── index.html  
└── traefik/  
    └── traefik.yml

Launching Traefik and Applications

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Now let's proceed with launching Traefik and the applications. To do this, create a docker-compose.yml file in the root project directory (test-traefik):

nano docker-compose.yml

Insert the following configuration:

version: "3.9"

services:
  traefik:
    image: traefik:v2.10
    container_name: traefik
    restart: always
    command:
      - "--configFile=/etc/traefik/traefik.yml"
    ports:
      - "80:80"
      - "8080:8080"
    volumes:
      - "./traefik/traefik.yml:/etc/traefik/traefik.yml"
      - "/var/run/docker.sock:/var/run/docker.sock:ro"

  app1:
    image: nginx:1.26-alpine
    container_name: nginx-app1
    restart: always
    volumes:
      - "./app1/default.conf:/etc/nginx/conf.d/default.conf"
      - "./app1/html:/usr/share/nginx/html"
    labels:
      - "traefik.enable=true"
      - "traefik.http.routers.app1.rule=Host(`app1.test.com`)"
      - "traefik.http.services.app1.loadbalancer.server.port=80"

  app2:
    image: nginx:1.26-alpine
    container_name: nginx-app2
    restart: always
    volumes:
      - "./app2/default.conf:/etc/nginx/conf.d/default.conf"
      - "./app2/html:/usr/share/nginx/html"
    labels:
      - "traefik.enable=true"
      - "traefik.http.routers.app2.rule=Host(`app2.test.com`)"
      - "traefik.http.services.app2.loadbalancer.server.port=80"

Use the following command to launch the containers:

docker compose up -d

If Docker Compose was installed using the docker-compose-plugin package, the command to launch the containers will be as follows:

docker-compose up -d

Check the status of the running containers using the command:

docker ps

All containers should have the status Up.

Let's verify whether the running containers with Nginx services can handle the traffic. To do this, send a request to the domain names using the curl utility.

For the first application:

curl -i app1.test.com

For the second application:

curl -i app2.test.com

As you can see, both services returned the previously specified messages.

Next, let's check the Traefik monitoring dashboard. Open a browser and go to the server's IP address on port 8080:

In the Routers section, you will see the previously defined routes app1.test.com and app2.test.com.

Conclusion

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Today, we explored Traefik's functionality using two Nginx services as an example. With Traefik, you can easily proxy applications running in Docker containers.