Networking in Docker-Compose

One of the many confusing things for beginners is how networking works in Docker-Compose.

It’s essentially you “Datacenter on a Laptop”. That means you can have virtual switches, routers and vpc’s, all on your laptop.

In this lecture we’re having a closer look at how this exactly works!

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Understanding the Basic Docker Bridge and Host Network

By default, docker creates an overlay network over all containers. A bridge. It’s called “docker0”. From the previous lectures there should be some networks left:

docker network ls

• Brings up a list of all networks

docker network prune

• Should delete all networks
• Just to clean up – you don’t have to do this, but sometimes it’s good to start fresh

docker network ls

• Should now just list the necessary networks for docker to function
• A bridge
• A host
• A null

docker run --rm --name my-webserver -d httpd

• Start an apache webserver (httpd container)
• Detached (-d)

docker inspect my-webserver

• Check the IP address of the container Open http://172.17.0.2  (or the IP address of your container)

• It won’t let you connect to it

• Unless you forward a port to your host with -p 8080:80 or so…

docker run --rm tomw1808/mycurl my-webserver

• Should download and run an image called “tomw1808/curl” which is just an ubuntu alpine with curl installed
• And curl “my-webserver”
  • Basically, the same as executing curl my-webserver on any Linux
• It will end in an error

docker run --rm tomw1808/mycurl 172.17.0.2

• Will output you the HTML of the Webserver
• “It Works!”

So, we can’t curl by name, we have to curl the exact IP Address

docker stop my-webserver

• Stops the webserver container

Hostname binding with Docker

Let’s see if we can also get Hostname-binding to work with Docker…

docker network create simple-network

• Creates a new bridge network called “simple-network”

docker run --rm -d --name my-webserver --network simple-network httpd

• Start the webserver again attaching it to the “simple-network” we created earlier

docker run --rm --network simple-network appropriate/curl my-webserver

• Now the name binding works
• “It Works!”

docker inspect my-webserver

• Get the IP Address of your webserver
• It should be 172.22.0.2 (or so – copy the IP of your container here)

docker run --rm tomw1808/mycurl IP-OF-MY-WEBSERVER(e.g. 172.22.0.2)

• Run curl without the network, on the docker0 network
• You won’t be able to connect to the webserver
• It’s segregated from the other network
• Ctrl-c to stop

docker stop my-webserver

• Stop the container again

docker network rm simple-network

• Cleanup: remove the simple-network again