As a software developer, Steve was given the task of building a microservice to handle incoming data from multiple sources. After creating a working prototype, he began to work on creating a container image for the microservice. Initially, he forgot about following any best practices, resulting in a bulky image with unnecessary components, making it challenging to maintain and update.
It wasn’t long before Steve realized that he needed to change his approach…
As we have learned in our previous post, containerization has become an essential part of modern software development, and in this post, we will delve into the process of creating container images, including the tools and techniques used to build, manage, and distribute container images.
We will also highlight the best practices for image management and discuss how to optimize your images to reduce their size, thereby improving the performance of your applications. Additionally, we will discuss how to manage your images by tagging, versioning, and organizing them in a registry. By the end of this post, you will have a clear understanding of how to create, manage, and optimize Docker images to deploy applications in a fast and efficient way.
Before we begin, let’s quickly refresh our memory. Containers are a way to package and distribute applications with all their dependencies and configurations, making it easier to run the applications on any system. Containers are lightweight and run isolated from each other, which provides a more secure and scalable environment for applications. Docker is a popular platform for creating, deploying, and running containers, and it uses images to package and distribute applications.
Now that we have that out of the way, let’s get started with creating Docker images!
Image Creation
Docker images are built using a set of instructions known as a Dockerfile. A Dockerfile specifies the base image, the application code, and the dependencies required to run the application. To build a Docker image, we run the
command and specify the path to the Dockerfile.docker build
Let’s work on the following step-by-step guide to building a Docker image based on the
web server, serving a simple HTML page:nginx
1. Create a new directory for your project and navigate into it:
mkdir my-nginx-project cd my-nginx-project
2. Create a new directory named html
in your project directory, and create a file named index.html
inside it. Here’s an example of what the index.html
file could look like:
<!DOCTYPE html> <html> <head> <title>My Awesome Website</title> </head> <body> <h1>Hello, World!</h1> <p>Welcome to my awesome website.</p> </body> </html>
3. Create a new file named Dockerfile
in your project directory, and open it in your favorite code or text editor.
# Use the official nginx image as the base image FROM docker.io/nginx:alpine # Copy the contents of the 'html' directory to the container COPY html /usr/share/nginx/html # Expose port 80 for HTTP traffic EXPOSE 80 # Set the default command for the container to start nginx CMD ["nginx", "-g", "daemon off;"]
Here are some explanations of each line:
# Use the official nginx image as the base image FROM docker.io/nginx:alpine
This line specifies that we want to build our image based on the latest nginx:alpine
official image.
# Copy the contents of the 'html' directory to the container COPY html /usr/share/nginx/html
This line copies the contents of the html
directory in our local file system to the /usr/share/nginx/html
directory in the container. The html
directory should contain the previously created index.html
file that will be served by nginx.
# Expose port 80 for HTTP traffic EXPOSE 80
This line specifies that the container should expose port 80, which is the default port for HTTP traffic.
# Set the default command for the container to start nginx CMD ["nginx", "-g", "daemon off;"]
The last line specifies the command that should be run when the container is started. In this case, we want to start nginx and keep it running in the foreground (rather than as a background process). You can check the Dockerfile reference for the full list of instructions.
4. Build the Docker image by running the following command in your project directory:
docker build -t my-nginx-image .
This command will build a new Docker image with the tag my-nginx-image
, using the Dockerfile
in the current directory (.
).
5. Check the Docker images on your local machine by running the following command:
docker images
You should see a list of all the Docker images on your local machine, including the my-nginx-image
image that you just created.
> docker images REPOSITORY TAG IMAGE ID CREATED SIZE localhost/my-nginx-image latest 0e081925bc1c 2 seconds ago 42.5 MB
6. To push the my-nginx-image
image to a Docker registry, you will first need to tag the image with the appropriate name. If you haven’t done so already, create an account on a Docker registry provider, such as Docker Hub, and log in to the registry using the docker login
command.
7. Tag the my-nginx-image
image with the appropriate registry and repository name by running the following command:
docker tag my-nginx-image <registry>/<username>/<repository>:<tag>
Replace <registry>
with the name of the Docker registry provider you are using (e.g. docker.io
for Docker Hub), <username>
with your username on the registry, <repository>
with the name of the repository you want to create on the registry, and <tag>
with a specific version tag for the image (e.g. latest
).
For example, if you are using Docker Hub and your username is myusername
, and you want to create a repository named my-nginx-repo
with the latest
tag, you would run:
docker tag my-nginx-image docker.io/myusername/my-nginx-repo:latest
8. Push the newly tagged image to the container registry by running the following command:
docker push <registry>/<username>/<repository>:<tag>
This command will upload the image to the Docker registry.
For example, using the same registry, username, repository, and tag as the previous step, you would run:
docker push docker.io/myusername/my-nginx-repo:latest
That’s it! You’ve successfully created a Docker image that serves a simple HTML page using nginx. If you want to make changes to the index.html
file, you can simply edit the file in your local html
directory and rebuild the Docker image using the docker build
command. Also, you pushed your Docker image to a registry, where it can be accessed by others.
Before moving into the best practices for image management and a talk a little about the different image building patterns I want for you to test your newly created container image, so, let’s run the following command:
docker run -p 8080:80 my-nginx-image
This command starts a new container based on the my-nginx-image
image, and maps port 8080 on your local machine to port 80 in the container.
Now visit http://localhost:8080 in your web browser to see the simple HTML page served by nginx. You should see the “Hello, World!” message displayed in your browser.
Image Management
Best practices for image management are critical for ensuring the security, reliability, and maintainability of your container images. Proper management of container images can help you avoid common pitfalls and improve the overall quality of your software development workflow. Here are some of the best practices for managing container images:
- Versioning
It’s important to version your container images so that you can easily track changes and revert to a previous version if necessary. You can version your images using a versioning system such as semantic versioning or by using tags, such as “latest”, “stable”, or “dev”.
- Tagging
Tagging allows you to label your container images with descriptive names that make it easier to manage and organize them. When you build a new container image, it’s a good practice to assign a tag to it so that you can easily identify it later.
- Security
Container images can contain security vulnerabilities, so it’s important to implement security best practices to minimize the risk of attacks. This includes regularly updating the base images and packages used in your images, and scanning images for known vulnerabilities.
- Image Size
Container images that are too large can lead to slow deployment times, so it’s important to keep your images as small as possible. This can be achieved by removing unnecessary files and packages, using multi-stage builds, and using a minimal base image.
- Layers
Container images are built from multiple layers, and it’s important to understand how these layers work and how to manage them effectively. By using the appropriate number of layers and minimizing the number of changes made in each layer, you can optimize your images for faster deployment and better security.
- Reusability
Reusing code and images can help you avoid duplicating effort and improve the overall efficiency of your workflow. By sharing images between teams and projects, you can take advantage of the expertise and experience of others, and save time and effort in the process.
- Maintenance
Regular maintenance of your container images is critical for ensuring their reliability and security. This includes updating base images and packages, and monitoring images for vulnerabilities.
By following these best practices for image management, you can ensure that your Docker images are secure, reliable, and efficient. This can help you to avoid common pitfalls, and improve the overall quality of your software development workflow.
Image Building Patterns
When it comes to building container images, there are several patterns and best practices that can be used to optimize the size and efficiency of the resulting image. In this article, we will explore some of the most popular container image building patterns, including the use of multi-stage builds.
1. Builder Pattern
The builder pattern is a common approach to building container images, where a separate “builder” image is used to build the application or service. The resulting artifacts are then copied into a smaller production image. The builder image typically contains all the build tools and dependencies needed to build the application, while the production image only contains the application itself and its runtime dependencies.
The benefits of using the builder pattern include reducing the size of the production image and improving security by reducing the attack surface. This approach can also make it easier to update the application in production since only the production image needs to be updated, while the builder image can remain unchanged.
2. Sidecar Pattern
In the sidecar pattern, a secondary container (the “sidecar”) is added to an existing container to provide additional functionality or services (resembling a sidecar attached to a motorcycle). For example, a sidecar container might be used to provide logging, monitoring, or security services. This approach can help simplify the application code by offloading complex tasks to separate containers, but can also increase the complexity of the overall system.
The benefits of using the sidecar pattern include improving the scalability and resilience of the application, as well as simplifying the application code. However, this approach can also add additional complexity, and care must be taken to ensure that the sidecar container does not become a single point of failure.
3. Ambassador Pattern
The ambassador pattern is similar to the sidecar pattern, but instead of adding a secondary container, a separate “ambassador” container is used to expose a service to the network, while the main container only communicates with the ambassador. The ambassador can perform tasks such as load balancing or SSL termination, and can provide a simplified interface for external services to communicate with the main container.
The benefits of using the ambassador pattern include improving the security and scalability of the system, as well as providing a more streamlined and simplified interface for external services. However, this approach can also add additional complexity and introduce additional points of failure.
4. Multi-Stage Builds
Multi-stage builds are a powerful feature of Docker that allow you to define multiple stages of the build process in a single Dockerfile. Each stage can use a different base image and set of dependencies, and the final image only includes the artifacts from the final stage. This approach can help reduce the size of the final image by eliminating unnecessary build artifacts and dependencies.
To use multi-stage builds, you define each stage of the build process as a separate FROM
statement in the Dockerfile. Each stage can use a different base image, and can perform different tasks such as compiling code or running tests. You can then use the COPY --from
statement to copy artifacts between stages, rather than relying on a shared volume or copying the files directly between containers.
For example, consider the following Dockerfile that uses multi-stage builds to create a final image for a Go web application:
# Stage 1: build the application FROM golang:1.16 AS build WORKDIR /app COPY . . RUN go build -o myapp # Stage 2: create the final image FROM nginx:1.23 COPY --from=build /app/myapp
In this post, we have discussed the process of creating container images, implementing best practices for image management, and utilizing container image building patterns such as the builder pattern, sidecar pattern, ambassador pattern, and multi-stage builds. Through these discussions, we emphasized the importance of following best practices for image management, such as image optimization and security, to ensure a successful deployment.
The insights gained from these discussions showed that the creation of container images is a crucial step in the containerization journey and must be approached with caution and proper planning. The use of container image building patterns not only streamlines the process but also provides a structured and organized approach to image management.
In the next blog post, we will delve into the exciting topic of launching containers from images and explore the various options and configurations available to guarantee a smooth and successful deployment of your containers. I look forward to continuing this journey with you and hope that you will join me for the next chapter of this series.
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