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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