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Docker Demo

Let's learn some docker.

Installation

Install Docker

Demo 1 - Running

Toying Around

Pull your image and check out the layers!

$ docker pull ubuntu
latest: Pulling from library/ubuntu
da7391352a9b: Pull complete 
14428a6d4bcd: Pull complete 
2c2d948710f2: Pull complete 
Digest: sha256:c95a8e48bf88e9849f3e0f723d9f49fa12c5a00cfc6e60d2bc99d87555295e4c
Status: Downloaded newer image for ubuntu:latest
docker.io/library/ubuntu:latest

Note that since we didn't specify an image tag, docker assumed we wanted the :latest image. What happens when we specify a new tag (that points to the same image as :latest)?

$ docker pull ubuntu:22.04

This command should succeed immediately because we've already pulled down the ubuntu:latest image, which is tagged to the same image as ubuntu:22.04. In fact, if we go on to the Ubuntu Docker Hub page, we can see that the README lists both 22.04 and latest as the same image!

Now what happens when we pull a slightly older image version?

$ docker pull ubuntu:20.04

In this case, we expect to see Docker downloading a new image because we do not have 20.04 already downloaded.

Now run it and play around in the container (ls, cd, cat, etc):

$ docker run -it --rm ubuntu /bin/bash

In another terminal, look at your active containers:

$ docker ps -a

You can close out of your open container, but before continuing, make sure all your containers have been cleaned up! This should have been handled via the --rm flag, but run docker ps -a to check. If you have any extras, you can use docker rm to delete them.

Using an image

Run the 2048 docker image:

$ docker run -it --rm alexta69/metube

Now it says that the application is running on port ___FILL_IN_PORT_HERE___. Go to localhost:___FILL_IN_PORT_HERE___ in your browser to see the application!

Wait, actually we cannot see anything. Why is that? That's because by default, the container is running on a different network than your host machine. We need to expose the port on the container to the host machine.

Can you figure out how to expose the application on port 8081 on your machine? The docker documentation might help.

Now, let's try to actually try to download some youtube videos. We recommend this one: https://www.youtube.com/watch?v=xvFZjo5PgG0.

If you have extra time right now, play around with some of the docker run flags. Some fun ones are -v, -d, --name, etc. You can check out the docker documentation for info on how these work. Also, you can google around and see if there are other interesting images. Maybe python or node?

Demo 2 - Building

We've provided you with a blank Dockerfile containing only a base nginx image. Nginx is a high-performance load balancer and webserver used across the industry. While Nginx has a complex feature set, all we need you to do is have it serve the static html files in the static/ directory.

There are many ways to do this, but we'd recommend using the COPY directive. How to use and where to copy to is an excercise left up to you, though! Maybe reading the nginx Docker Hub docs will be helpful.

Once you think you've got the Dockerfile right, use docker build . -t nginx-demo to build the container to the name nginx-demo.

When you've got the image built, try to run the container! Remember that the nginx image runs on port 80. Is there a way (using syntax you've already learned) to bind port 8081 on your machine to port 80 on the container?

If the container is running successfully, go to localhost:8081 in your browser to see if it worked!

If you've got some extra time here, you've got a few options:

  1. Download some more youtube videos
  2. Try to get the downloaded content to be persistent (if you turned off the docker container and restarted it,previous downloads still exist) using volume mounts.
  3. Go for the extra credit below

Extra Credit - Reverse Proxy

While Nginx can be used as a standalone webserver, it's usually used as a reverse proxy (load balancer) in industry.

For extra credit, implement the following behavior using only the docker CLI and the nginx configuration file:

  • If the webserver is accessed at localhost, serve the website we've given to you here.
  • If the webserver is accessed at 127.0.0.1, forward the request to the YouTube Downloader container.

Concretely, if you go to localhost:8081 in your browser, you should see the site we gave you. If you go to 127.0.0.1:8081, you should see Youtube Downloader.