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Introduction to Containers in Practice

This repo contains files and scripts help you get Docker installed and up and running, and helps you step through the workshop.

If you don't already have Git installed, take a look at install-git.sh.

Installing Docker

Take a look at install-docker.sh.

The Docker installation documentation can be found at: https://docs.docker.com/install/linux/docker-ce/ubuntu/#install-docker-engine---community-1

Run your first container

Take a look at test-docker.sh.

This runs a container that prints "Hello, world!"

Run an Nginx container

Here's where it gets interesting. Instead of installing Nginx on your machine, you can run it as an (ephemeral) container.

Take a look at run-nginx.sh.

Nginx will be available on port 80 (the running container port 80 is mapped to your host port 80). Once you stop the container, everything is deleted.

Lots of languages

Containers can be a neat way to partition programming language runtimes. If you've used virtual environments in Python or installed more than one JVM, you'll know it's a faff. The dedicated filesystem in a container is a great way to do it reliably.

Head into the languages folder and try these scripts:

Congratulations, you've just polyglotted your world with a single, standard way to run code written in any language. You could run bash, C code, even Perl if that's your thing. It's "just" a Linux process, so anything you can run, you can containerise.

Container scheduling with Compose

We could install Kubernetes, but let's be honest, it'll take too long. Ain't nobody got time for that. We'll illustrate container scheduling using Docker Compose.

Head into the compose folder and take a look at install-docker-compose.sh.

The Docker Compose installation documentation is at: https://docs.docker.com/compose/install/

Now take a look at docker-compose.yml.

Much like Kubernetes, this is a declarative Yaml descriptor for the desired state of a system.

The Docker Compose file reference is at: https://docs.docker.com/compose/compose-file/

We'll be running:

  • An Nginx reverse proxy
  • A Python app (you don't need Python installed)

Nginx: take a look at default.conf - this file will be mounted into the nginx container to configure the reverse proxy. You may have noticed we're using ephemeral containers, so we're injecting configuration to a standard, vendor-maintained image at runtime.

Python app: if you'd like to explore the Python app we'll be runinng, head into the python-app folder. Unlike the standard Nginx container, here we're building a custom image. You can run the app stand-alone using the docker-build.sh and docker-run.sh scripts.

To apply our declararation and run the containers we've specified, head back to the compose directory and start Docker compose:

  • docker-compose up

This will read docker-compose.yml, start the Nginx and Python containers, attach them to a default shared network and enable them to discover each other using the service names in the compose file.

Try this:

  • docker ps - display running containers
  • docker exec -it compose_nginx_1 sh - execute the command sh inside the nginx container (note the name provided by docker ps)
  • apt update && apt install curl - modify the running container. Remember the container is ephemeral, so if you restart the container, these changes will be lost.
  • curl app:5000 - connect to the app container by DNS name
  • Exit from the shell in the container and run docker-compose scale app=2 - you now have two instances. Try docker ps to confirm.
  • Start a new shell in the nginx container. This time, apt install dnsutils and then dig app - you should get an IP address for each running app container.

Short link for this repo: https://carb.onl/docker-workshop

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Step through installing and using Docker in practice.

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