Overriding the default command

Overriding the start command of an image has many uses. One of them is testing or debugging something in an image that already has a start command with a specific use case. For example, the postgres image starts a database if you start it normally. To be able to dive into the image and look at configuration files or debug an issue you're having; you can start it with the bash command, an often available shell. What is the command to start the postgres image interactively with a bash shell?

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Introduction to Docker

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Introduction to Docker

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You'll go from starting and stopping your first container to seeing how to clean your environment by removing all containers and images. You'll see how to debug issues by running commands inside a container or executing bash commands in a container interactively. All of this is done using the Docker Command Line Interface.

Exercise 1: Running Docker containers Exercise 2: Running your first container Exercise 3: Running a container in the background Exercise 4: An interactive container Exercise 5: Working with Docker containers Exercise 6: Helping a colleague Exercise 7: Cleaning up containers Exercise 8: Managing local docker images Exercise 9: Pulling your first image Exercise 10: Pulling a specific tag Exercise 11: Cleaning up images

Once you are able to manage images and containers, it's time to know how to share images with colleagues or your entire company and to understand how to create your own. Now, you'll build your own images using Dockerfiles. Dockerfiles are text files that include everything needed for Docker to build an image. You'll learn how to create images and will get an introduction to all the essential Dockerfile instructions like FROM, RUN, COPY, and more. By the end of this chapter, you'll have insight into how Docker makes images and be able to create optimized Docker images from scratch.

Exercise 1: Distributing Docker Images Exercise 2: Sharing your work using a Docker registry Exercise 3: Saving an image to a file Exercise 4: Receiving Docker Images Exercise 5: Creating your own Docker images Exercise 6: Building your first image Exercise 7: Working in the command-line Exercise 8: Editing a Dockerfile Exercise 9: Creating your own Dockerfile Exercise 10: Managing files in your image Exercise 11: Copying files into an image Exercise 12: Copying folders Exercise 13: Working with downloaded files Exercise 14: Choosing a start command for your Docker image Exercise 15: Overriding the default command

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Exercise 16: Pulling a specific tag Exercise 17: Adding a CMD

In this final chapter, you’ll focus on making your Dockerfiles configurable and secure. You'll learn how to make your Dockerfiles configurable using the ARG and ENV instructions. You’ll see why changing the user in your images makes them more secure and how to use the USER Dockerfile instruction to do so. To wrap things up, you’ll learn about some essential security best practices when creating Docker Images.

Exercise 1: Introduction to Docker caching Exercise 2: Docker caching Exercise 3: Ordering Dockerfile instructions Exercise 4: Changing users and working directory Exercise 5: WORKDIR and USER Exercise 6: Setting the user Exercise 7: Setting the working directory Exercise 8: Variables in Dockerfiles Exercise 9: Understanding ARG and ENV Exercise 10: Overriding ARG in a build Exercise 11: Changing behavior when starting a container Exercise 12: Creating Secure Docker Images Exercise 13: Security best practices Exercise 14: Keeping packages up-to-date Exercise 15: Be safe, don't use root