How to use docker scout quickview command to get image overview

Introduction

In this lab, you will learn how to use the docker inspect command to obtain a quick overview of Docker images. You will explore how to get detailed information about a specific image, identify and inspect the most recently built image, and understand how to extract relevant data from the inspection output using formatting options. The lab will guide you through practical examples using sample images and a simple Dockerfile.

Skills Graph

Get a quick overview of a specific image

In this step, you will learn how to get a quick overview of a specific Docker image using the docker inspect command. This command provides detailed information about a Docker object, including images, containers, volumes, and networks.

First, let's pull a sample image that we can inspect. We will use the hello-world image, which is a very small image used for testing.

docker pull hello-world

You should see output indicating that the image is being pulled and downloaded.

Now that we have the image, we can use docker inspect to get information about it.

docker inspect hello-world

This command will output a large JSON object containing various details about the hello-world image, such as its ID, creation date, architecture, operating system, and configuration.

To get a quick overview, you might be interested in specific fields within this JSON output. You can use the -f or --format flag with docker inspect to specify a Go template that formats the output. For example, to see the image ID and creation date, you can use the following command:

docker inspect -f '{{.Id}} {{.Created}}' hello-world

This command will output the image ID followed by its creation timestamp. The {{.Id}} and {{.Created}} are placeholders that refer to the Id and Created fields in the JSON output of docker inspect.

You can explore other fields in the JSON output from the full docker inspect hello-world command and use them in your format string to get the specific information you need.

Get a quick overview of the most recently built image

In this step, you will learn how to identify and get a quick overview of the most recently built Docker image. This is useful when you are actively developing and building images and want to quickly inspect the latest version.

First, let's create a simple Dockerfile to build an image. In your ~/project directory, create a file named Dockerfile with the following content:

FROM alpine:latest
RUN echo "Hello, Docker!" > /app/message.txt
CMD cat /app/message.txt

This Dockerfile uses the alpine base image, adds a file named message.txt with the content "Hello, Docker!", and sets the command to print the content of this file when the container runs.

Now, build the Docker image using the docker build command. We will tag it with my-recent-image.

docker build -t my-recent-image .

The . at the end of the command indicates that the Dockerfile is in the current directory (~/project). You will see output showing the build process.

After the build is complete, you can list your images using docker images.

docker images

You should see my-recent-image listed, along with the hello-world image from the previous step and the alpine base image. The most recently built image will typically appear at the top of the list or have the most recent creation time.

To get a quick overview of the most recently built image, you can combine docker images with command-line tools like head and awk to extract the image ID of the first image listed (which is usually the most recent). Then, you can use docker inspect with that ID.

docker inspect $(docker images -q | head -n 1)

Let's break down this command:

• docker images -q: This lists only the image IDs.
• head -n 1: This takes the first line of the output, which is the ID of the most recent image.
• $(...): This is command substitution, which executes the command inside the parentheses and substitutes its output into the outer command.
• docker inspect ...: This inspects the image with the ID obtained from the command substitution.

This will output the detailed JSON information for the most recently built image. You can again use the -f flag with docker inspect to format the output as needed, similar to the previous step.

For example, to see the ID and creation date of the most recent image:

docker inspect -f '{{.Id}} {{.Created}}' $(docker images -q | head -n 1)

This provides a quick way to get key information about the image you just built.

Get a quick overview from an SPDX file

In this step, you will learn how to obtain a quick overview of the software components within a Docker image by generating and examining an SPDX (Software Package Data Exchange) file. SPDX is an open standard for communicating software bill of materials (SBOM) information, including components, licenses, and copyrights.

Generating an SPDX file for a Docker image requires a tool that can analyze the image layers and extract the necessary information. One such tool is syft, a command-line tool for generating SBOMs from container images and filesystems.

Since syft is not pre-installed, we will download and install it. We will download the latest release for Linux.

curl -sSfL https://raw.githubusercontent.com/anchore/syft/main/install.sh | sudo bash -s -- -b /usr/local/bin

This command downloads the installation script for syft and executes it with sudo to install the binary to /usr/local/bin. You might be prompted for your password, but the labex user has passwordless sudo.

After installation, you can verify that syft is installed by checking its version:

syft version

You should see the version information for syft.

Now, let's generate an SPDX file for the my-recent-image we built in the previous step. We will output the result to a file named my-recent-image.spdx.json in the ~/project directory.

syft my-recent-image -o spdx-json > ~/project/my-recent-image.spdx.json

This command tells syft to analyze the my-recent-image and output the results in SPDX JSON format, redirecting the output to the specified file. This process might take a moment depending on the size of the image.

Once the command completes, you will have an SPDX JSON file containing a detailed inventory of the software packages found within the image. You can view the contents of this file using a text editor like nano:

nano ~/project/my-recent-image.spdx.json

Inside the file, you will find information about the image itself and a list of packages detected, including their names, versions, and licenses. This provides a quick overview of the software components present in your image without needing to run the container or inspect individual layers manually.

You can scroll through the file to see the different sections and the information they contain. Look for the packages array, which lists the detected software components.

Press Ctrl + X to exit nano.

Summary

In this lab, you learned how to obtain a quick overview of Docker images using the docker inspect command. You practiced inspecting a specific image by pulling the hello-world image and using docker inspect to view its detailed information in JSON format. You also learned how to use the -f flag with docker inspect and Go templates to extract and format specific fields like the image ID and creation date, allowing for a customized quick overview.

Furthermore, you explored how to identify and inspect the most recently built Docker image, which is particularly useful during active development cycles. This involved understanding how to list images and potentially filter or sort them to find the latest one for inspection.