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Application Containerisation

Containers are similar to VMs, except that while VMs create new kernels, containers typically share kernels and operating level resources with the host system. This results in faster boot times in exchange for lower levels of isolation.

Section Objectives

  1. Concepts in container technologies
  2. Introduction of the Dockerfile
  3. Understand and use basic Docker commands
  4. Build, configure and deploy a container
  5. Optimising image specification files

Concepts and Introduction to Docker

Model of Container Technologies

There are three main entities in container technologies - the image specification, the image, and the container.

The image specification is a blueprint of what the image will contain. Developers run docker build to create the image.

The image is a result of the build process. Think of images as logical classes which can then be instantiated by docker run into a container.

Containers are basically instances of images, implying that multiple containers can be generated from an image.

Introduction to the Dockerfile

The Dockerfile is a directive based image specification file that tells Docker how an image should be built. Thus, the Dockerfile will contain some, all, or more of the following basic directives:

Directive Description
FROM Indicates which operating system we should be using
ARG Specifies build-time only arguments
ENV Specifies environment variables that persist after build-time
RUN Indicates commands to be run when docker build is executed
COPY Copies files from your local machine into the image
ENTRYPOINT Specifies the command to be run when the image is instantiated into a container.
WORKDIR Specifies the working directory - where the container should start from

Understand Basic Docker Commands

Here are some basic CLI commands to get started. We will cover their practical use cases in the activites of this section. All of the following commands should be prefixed with docker when executing in your terminal.

Command Description
build Builds a Dockerfile
container ls Lists all running containers
container ls -a Lists all containers
network ls Lists all networks
image ls Lists all images
volume ls Lists all volumes
top <CONTAINER_ID> Shows statistics on all running containers
run Instantiates an image into a container
exec -it Executes into a specified container

Activity 1: Using an existing Docker Image

Click here for Activity #1.

Activity 2: Crafting a Dockerfile

Click here for Activity #2.

Next Steps

Click here to move onto Provisioning an Environment.