How to use docker buildx history export to export build history

Introduction

In this lab, you will learn how to utilize the docker buildx history export command to manage and export your Docker build history. We will begin by building a simple Docker image and examining its build history using the docker history command.

Following that, you will learn how to export the build history of a specific image to a file. Finally, we will explore how to export all build records for a given builder, providing a comprehensive overview of your build activities. This lab will equip you with the skills to effectively track and manage your Docker image build processes.

Skills Graph

%%%%{init: {'theme':'neutral'}}%%%% flowchart RL docker(("Docker")) -.-> docker/ImageOperationsGroup(["Image Operations"]) docker(("Docker")) -.-> docker/DockerfileGroup(["Dockerfile"]) docker/ImageOperationsGroup -.-> docker/images("List Images") docker/DockerfileGroup -.-> docker/build("Build Image from Dockerfile") subgraph Lab Skills docker/images -.-> lab-555049{{"How to use docker buildx history export to export build history"}} docker/build -.-> lab-555049{{"How to use docker buildx history export to export build history"}} end

Build a simple image and view its history

In this step, we will learn how to build a simple Docker image and view its history. Building a Docker image involves creating a Dockerfile, which is a text file that contains all the commands a user could call on the command line to assemble an image.

First, navigate to the ~/project directory if you are not already there.

cd ~/project

Now, let's create a simple Dockerfile. We will create a file named Dockerfile in the ~/project directory.

nano Dockerfile

Add the following content to the Dockerfile:

FROM ubuntu:latest
RUN echo "Hello, Docker!" > /app/hello.txt
CMD ["cat", "/app/hello.txt"]

This Dockerfile does the following:

FROM ubuntu:latest: This line specifies the base image for our new image. We are using the latest version of the Ubuntu image from Docker Hub.
RUN echo "Hello, Docker!" > /app/hello.txt: This line executes a command during the image build process. It creates a directory /app and writes the text "Hello, Docker!" into a file named hello.txt inside that directory.
CMD ["cat", "/app/hello.txt"]: This line specifies the default command to run when a container is started from this image. It will execute the cat /app/hello.txt command, which will print the content of the hello.txt file.

Save the file and exit the nano editor (Press Ctrl + X, then Y, then Enter).

Now, let's build the Docker image using the docker build command. We will tag the image with the name my-hello-image and the tag latest. The . at the end of the command indicates that the Dockerfile is located in the current directory.

docker build -t my-hello-image:latest .

You will see output indicating the build process, showing each step being executed.

After the image is built, you can view the history of the image using the docker history command. This command shows the layers that make up the image and the commands that were used to create each layer.

docker history my-hello-image:latest

The output will show a table with information about each layer, including the layer ID, the command used, the creation time, and the size. This history is useful for understanding how an image was built and for debugging build issues.

Export the build history to a file

In the previous step, we viewed the build history of our Docker image directly in the terminal. In this step, we will learn how to export this build history to a file for later analysis or sharing.

We can redirect the output of the docker history command to a file using the standard output redirection operator >. Let's export the history of the my-hello-image:latest image to a file named history.txt in the ~/project directory.

Make sure you are in the ~/project directory:

cd ~/project

Now, execute the following command to export the history:

docker history my-hello-image:latest > history.txt

This command will execute docker history my-hello-image:latest and instead of displaying the output on the screen, it will write the output to the file history.txt.

You can verify that the file has been created and contains the build history by viewing its content using the cat command:

cat history.txt

You should see the same build history information that you saw in the previous step, but now it is stored in the history.txt file. This file can be easily shared or used for documentation purposes.

Exporting the build history to a file is a useful practice for keeping records of how your Docker images are built, which can be helpful for debugging, auditing, and collaboration.

Export all build records for the builder

In the previous steps, we built a Docker image and exported its history. Docker BuildKit, the default builder for Docker, keeps records of all build operations. In this step, we will learn how to export all these build records.

To export all build records, we can use the docker buildx build command with the --metadata-file flag. This flag allows us to specify a file where the build metadata, including the build records, will be written in JSON format.

First, ensure you are in the ~/project directory:

cd ~/project

Now, let's build the image again, but this time we will export the build metadata to a file named build-records.json. We will use the same Dockerfile we created in the first step.

docker buildx build --metadata-file build-records.json -t my-hello-image:latest .

The docker buildx build command is part of the Docker Buildx plugin, which provides enhanced build capabilities. The --metadata-file build-records.json flag tells BuildKit to write the build metadata to the specified file.

After the build completes, a file named build-records.json will be created in the ~/project directory. This file contains detailed information about the build process in JSON format.

You can view the content of the build-records.json file using the cat command:

cat build-records.json

The output will be a JSON object containing various details about the build, including information about the build steps, the resulting image, and other metadata. This comprehensive record can be valuable for advanced analysis, automation, and integration with other tools.

Exporting build records provides a more detailed view of the build process compared to just the image history, offering insights into the execution of each build step and the dependencies involved.

Summary

In this lab, we learned how to build a simple Docker image by creating a Dockerfile with instructions for the build process, including specifying a base image, running commands during the build, and defining the default command for containers. We then used the docker build command to create the image and tagged it for easy identification.

Following the image build, we explored how to view the history of the image using the docker history command, which provides insights into the layers and commands used to construct the image. The lab then guided us through exporting the build history of a specific image to a file using docker buildx history export and subsequently exporting all build records for the current builder, demonstrating how to preserve and review build details.