Reverse Proxy for Docker Containers

What are we building?

We are creating our own dynamic reverse proxy similar to Traefik. This project serves as a learning exercise to better understand Docker networking and reverse proxy management.

Tools Used:

• Node.js / Express.js
• Ports:
  • 8080: Management API for starting, stopping, and listening to containers.
  • 80: For reverse proxy routing.

What is a Reverse Proxy?

A reverse proxy sits between the client and backend servers, routing client requests to the appropriate server. In environments with multiple servers, it is necessary to manage which server should handle a given request. A reverse proxy like Nginx or Traefik can use load-balancing algorithms, such as Round Robin, to distribute the traffic.

In simpler terms:

• The reverse proxy intercepts requests from the client.
• It forwards them to one of the backend servers based on predefined rules or dynamic routing.

Docker Reverse Proxy

In a Docker environment, a reverse proxy helps in routing traffic between multiple running containers. Typically, you would need to manually configure ports when adding or removing containers, but with a dynamic reverse proxy, this can be done automatically.

Traefik, for example, updates its routing configuration dynamically as containers are added or removed, saving manual effort.

Short Note on Docker Networking

Let's explore a simple use case with Docker networking.

Running an Nginx container:

docker run -d nginx

This command runs a container but it won’t be accessible from your host machine as it operates inside Docker's virtual network, with port 80 being private to the container.

To expose the port:

docker run -d -p 8080:80 nginx

In this case, port 8080 on the host machine is mapped to port 80 of the Nginx container, allowing access from the host.

Problem: Managing Multiple Containers

If you have multiple Nginx containers:

docker run -d -p 8080:80 nginx
docker run -d -p 8081:80 nginx

Managing and remembering the ports of multiple containers quickly becomes cumbersome, especially as the number of containers grows.

Enter Traefik

Traefik solves this by automatically managing the routing for multiple containers. You only need to start a Traefik container, and it will handle the rest.

• Start a Traefik container and map it to port 80.
• Spin up any number of containers and Traefik will dynamically route traffic to them without manual intervention.

For example, if you spin up two containers named nginx1 and nginx2, Traefik will create subdomains for both:

• nginx1.docker.localhost
• nginx2.docker.localhost

You can now access them via these subdomains without needing to expose individual ports, enhancing security and simplifying management.

Benefits of using Dynamic Reverse Proxy

• Dynamic Routing: Automatically configures routes when containers are added or removed.
• Enhanced Security: Containers are accessed via Traefik, not directly via exposed ports.
• Ease of Use: Reduces manual effort when managing a large number of containers.