Docker CLI

Overview

• You start with a Docker file and list out everything you need for your container.
  • The operating system, the software, and any other necessary information.
• When you build a Docker file it results in a Docker image.
  • an image is a read-only lightweight executable snapshot of the operating system’s state.
• executing docker run ${name-of-image} results in a container on a Docker host.

3 Main Components of Docker

• Docker has 3 main components.
  1. The Docker daemon.
  2. The Docker CLI.
  3. And the image registry.
• We’ll be talking about each of these components

Docker Client

• The Docker client provides developers a way to interact with Docker through a Command Line Interface or CLI.
• This is how you issue commands to Docker to build your containers, run your containers, or stop your containers.
• When you use the CLI you’ll type a command into your terminal that starts with Docker.

Docker Client API

• run the docker stop command to stop the containers
• commands can manage the complete lifecycle of the containers.
  • docker create
    • creates a container but does not start it
  • docker run
    • creates and starts a container in one operation
  • docker rm
    • deletes a container

Docker Daemon

• the environment to interpret and execute the client commands
• Provides container access to
  • network ports
  • storage volumes
  • or any other components at the operating system level

Docker Image

• The blueprint for how to build a container is called a Docker image.
  • A container is a running instance of an image
• An image is a lightweight executable package that includes everything a system needs in it.
  • application code, software, dependencies, and config variables.
• They are read only artifacts.
  • A container cannot be changed unless you build a new image.
• After creating an image, we place it in the Image Registry.

Image Registry

• the Image Registry is a place to store your Docker images
• A registry makes it possible for the Docker daemon to retrieve your Docker images.
• It is analogous to a source code repository, like github, to store your code.
  • dockerhub is an non-AWS alternative

Image Registry Behaviors

• The image registry allows you to
  • push your container images as needed.
  • pull your container images as needed.

Image Registry Accessibility

• Registries can be either
  • public - images are shared with the whole world.
  • private - images are only shared amongst members of an enterprise or a team.

Creating container

• To instantiate an image is to create a container from an image.
• A container is a running instance of an image
• You can think of it as an encapsulated environment to run your applications that only has access to the resources that are provided in the Docker image.
• To create a container on a Docker host from the Image Registry, docker run through the Docker CLI.
• The Docker client will then delegate that command to the Daemon.

docker run

• docker run takes care of everything you need to start up a container.
• Upon receiving the run command, the Daemon lazy fetches the
  • If the image does not exist, on host, then pull image from Image Registry to host.
  • Use image on host to create container.

Docker File

• So how do we get the image in the first place?
• That would be through something called a Docker file.
• A Docker file is a plain text, standardized template, that you create with instructions that informs Docker how your image should be built.

Docker File

(Continued)

• It’s a script that contains a list of commands that the Docker client will call when putting your image together.
• It includes instructions for provisioning
  • operating system installation
  • prerequisite software installation
  • additional dependency installations
  • environment configuration
• When you use the docker build command through the CLI, on a particular Docker file, it results in a Docker image.

Summary

• Now that we have all the pieces lets quickly summarize this.
• You start with a Docker file and list out everything you need for your container.
  • The operating system, the software, and any other necessary information.
• When you build a Docker file it results in a Docker image.
  • Which is just a lightweight executable package.
• When you run that executable using that Docker run command it then results in a container on a Docker host.