05-Linking

Linking Containers

To understand container to container networking it helps to understand how manual linking of containers works.

Let's run a new container with our node app from section 3

docker run -d --name app hello-node

Note: we have not mapped the container port 80 to a host port this time. Also make a note of the container id for later

Nginx

Nginx is a web server that is often use as the public front end to applications like a dotnet app or nodejs. This way we will get better logging, SSL termination etc.

• First have a look at the nginx.conf file
• Then check out our Dockerfile

Let's start up a new container with nginx in it that will proxy through to our node app.

docker build -t nginx-app .
docker run -d -p 8080:8888 --link <node container id>:app nginx-app

• Preview the running application

So what just happened?

• -p 8080:8888 - Expose the container port 8888 as 8080 on the host
• --link <id>:app - Link through to the node app and name the relationship app
• The nginx.conf says proxy through to the url http://app:80
• We didn't need to expose a port on the app container

So how was it able to address the app container with the name app?

# Get the container ids
docker ps

# exec into the nginx container
docker exec -it <nginx id> /bin/bash

# let's look at the hosts file
cat /etc/hosts

exit

Pretty clever, huh?

Cleanup

docker kill `docker ps -q`