Context

I’ve started to use docker at work and I have a personal server that hosts 2 websites on a single nginx instance, with 2 virtual hosts configured (a.k.a. server). So the idea is to upgrade the architecture to embrace the docker way, and also improve my knowledge about docker.

Each website should run on its own container, and a reverse proxy will route the traffic.

Implementation

Step1

Let’s create a new project, divided in 3 folders : site1, site2, proxy. One folder for each container.

proxy
  Dockerfile
  conf
    conf.d
      site1.conf
      site2.conf
site1
  Dockerfile
  index.html
site2
  Dockerfile
  index.html

Here is the content of site1.conf, the reverse proxy configuration for site1 :

server {
    listen       80;
    server_name  site1;

    location / {
        proxy_pass   http://192.168.59.103:8080/;
    }
}

Let’s run the containers :

docker run -d -p 8080:80 ymn/site1
docker run -d -p 8081:80 ymn/site2
docker run -d -p 80:80 ymn/proxy

I can test direct access

curl "http://docker:8080/"
curl "http://docker:8081/"

and proxified access

curl "http://site1"
curl "http://site2"

What could be improved :

proxy_pass contains a hardcoded IP address
The 3 containers should be started manually
The ports of site container are publicly exposed

Step2

To avoid exposing ports, Docker allows linking containers together.

Here is how to run containers

docker run -d --name site1 ymn/site1
docker run -d --name site2 ymn/site2
docker run -d -p 80:80 --name proxy --link site1 --link site2 ymn/proxy

As you can see, containers now have names, because Docker linking is based on the name.

Here is the new configuration for the proxy

server {
    listen       80;
    server_name  site1;

    location / {
        proxy_pass   http://site1/;
    }
}

With the link, the proxy container knows how to connect to site1. In fact, Docker adds a host entry for site1 to the /etc/hosts of the proxy container.

Step3

Command lines are now very long and it becomes painful to run the whole thing. Hopefully, there is a tool in the fast-growing Docker ecosystem that will help us : docker-compose.

We just have to define our multi-container application with a configuration file in YAML to describe how to run our 3 containers

proxy:
  build: proxy
  ports:
  - 80:80
  links:
  - site1
  - site2
site1:
  image: ymn/site1
site2:
  image: ymn/site2

And we can run all containers with a single command : docker-compose up

Step 4

The setup is now quite good. But there are still ways to improve. Docker exposes a remote API that allows automating many tasks. So some projects leverage this API, like nginx-proxy which generate automatically the config of the proxy:

docker run -d -p 80:80 -v /var/run/docker.sock:/tmp/docker.sock:ro jwilder/nginx-proxy
docker run -d -e VIRTUAL_HOST=site1 ymn/site1
docker run -d -e VIRTUAL_HOST=site2 ymn/site2

Playing with Docker and nginx : from multi-domain to multi-container