Multi-Stage Magic: Building Docker Images in Phases


Software development has evolved significantly over the years, and Docker has become an essential component for modern software development. Docker is a platform that allows developers to create, deploy, and manage applications in a containerized environment.

It provides a standardized approach to building, shipping, and running applications across any infrastructure. Docker has rapidly gained popularity due to its ability to improve the development process by providing an efficient way of packaging software with its dependencies.

One of the challenges developers face with traditional application deployment is the complexity of environment management. In contrast, Docker aims to simplify this process by creating an isolated environment (container) that encapsulates all required dependencies for your application.

This means that developers can quickly move between environments and have confidence that their code will run correctly in any setting. In this article, we explore multi-stage builds in Docker images – an advanced technique that helps create lightweight and efficient images while reducing build times.

Multi-stage builds allow you to break down the build process into multiple stages or phases, each serving a specific purpose towards creating the final image. Let’s dive deeper into how multi-stage builds work and what benefits they offer over traditional image building techniques.

Explanation of Docker and Its Importance in Modern Software Development

Docker is known as a containerization platform that allows developers to package up their applications into standard units (containers). Containers are then executed under isolated conditions on various operating systems like Windows or Linux machines.

Docker simplifies the complexity surrounding environment management by providing a standardized approach for deploying software across environments efficiently. With Docker containers, developers can bundle their applications with dependencies such as libraries or frameworks within one package so they can be easily moved between different environments without worrying about compatibility issues.

This portability is essential because it enables faster testing cycles since moving from one environment to another is seamless. This feature allows developers to build and test their applications quickly, ensuring that their code behaves correctly in the target environment.

Brief Overview of Multi-Stage Builds and Their Benefits

Multi-stage builds take the concept of standard Docker image building to a new level by allowing you to break down your build process into multiple stages. Each stage performs a specific function, such as downloading dependencies or compiling source code.

Once each stage completes its task, it creates an intermediate image that is used by the subsequent stage. The key advantage of multi-stage builds is that they enable you to create lightweight and fast Docker images by eliminating unnecessary artifacts generated during the build process.

This makes your images smaller, faster, and easier to deploy. By separating each stage into its own containerized environment, you can also ensure that each step is performed optimally without interference from other processes.

Another significant advantage of multi-stage builds is that they can significantly reduce build times since individual stages can be cached after they complete their respective tasks. This caching allows subsequent builds to reuse these intermediate images rather than starting the entire build process from scratch every time, thereby saving significant time when building large-scale applications with many dependencies.

Understanding Multi-Stage Builds

Definition of multi-stage builds

Docker is a popular platform that automates the deployment and management of applications in containers. It enables developers to package their application code, along with all its dependencies, into a single container that can be deployed anywhere.

However, as Docker images grow in size due to the accumulation of various dependencies, it becomes challenging to manage them efficiently. Multi-stage builds address this issue by providing developers with an efficient way to build Docker images.

A multi-stage build is a Docker feature that allows developers to create stages in a Dockerfile, each with its own set of instructions and dependencies. The final image is then built from the last stage.

Explanation of how they work

The primary concept behind multi-stage builds is the ability to separate the build process into multiple stages or layers. Each stage has its own set of commands and dependencies that are necessary for building an application or component inside a container. Once one stage completes successfully and produces an output required for the next stage, it creates a new layer on top of the previous one.

This approach allows developers to optimize the final image’s size by removing unneeded files and libraries from intermediate stages as they progress towards building their desired outcome. For instance, by installing all necessary development tools and libraries in one stage, then copying only compiled artifacts into another stage dedicated solely for running those artifacts.

Comparison to traditional Docker image building

Traditional Docker image building involves creating an image based on a base image such as Ubuntu or Alpine Linux by adding layers upon layers until all dependencies are installed before copying files or artifacts into the container. However, this approach can result in large images containing many unnecessary packages and libraries since every software package added during development remains within each layer until removed explicitly.

Multi-stage builds offer several advantages over traditional Docker image building. They significantly reduce the final image size, as unused dependencies and tools are removed during the build process, making the image more secure, easier to maintain, and deployable across different environments.

The Magic of Multi-Stage Builds

Benefits of Multi-Stage Builds

Deploying Docker images is an essential step when it comes to software development, and it can be a time-consuming process. Multi-stage builds have significantly improved the efficiency and speed of Docker image building. In this section, we will discuss the benefits of multi-stage builds in terms of reduced image size and increased speed and efficiency compared to traditional Docker image building.

Reduced Image Size

One significant benefit that multi-stage builds offer over traditional Docker image building is a reduced image size. This reduction in size is due to the fact that multi-stage builds allow developers to separate build-time dependencies from runtime dependencies.

In other words, you no longer need to include all the tools used during development or build stages in your final production image. By using multi-stage builds, you can create multiple images with each stage having its own set of dependencies.

For instance, you can have one stage for compiling code, another for testing purposes, and one for packaging code into a final distribution package. By doing so, you reduce the number of layers required in your final production image.

Comparison to Traditional Docker Image Building

Traditional Docker image building requires developers to include all build-time dependencies like compilers or libraries in their final production images. This approach results in larger images that are more challenging to manage and deploy efficiently.

Multi-stage builds provide a solution by allowing developers to keep build-time dependencies separate from runtime dependencies. As a result, each stage can have its own environment with just the necessary tools needed at that specific stage while discarding any unnecessary files or configurations.

The end result? Smaller images!

Increased Speed and Efficiency

Another significant benefit that comes with using multi-stage builds is increased speed and efficiency when it comes to building Docker images. By dividing the build process into smaller stages, each stage can be optimized to run faster, thus making the entire build faster.

Since each step of the build process can be parallelized and executed independently of other steps, developers can utilize computing resources more efficiently and enable quicker builds. Additionally, by optimizing each stage separately, you can ensure that only what’s necessary is being used, further increasing efficiency.

Comparison to Traditional Docker Image Building

In traditional Docker image building, as mentioned earlier in this section, all dependencies are included in a single image. This approach results in slower builds due to the size of images and complexity of managing them. Since multi-stage builds allow for separate stages with individual environments optimized for specific tasks, it takes far less time to complete the entire process.

Furthermore, since each stage is focused on one particular task or set of tasks rather than attempting to execute everything at once in a single environment like traditional builds do means that there is much less overhead involved in staging containers using multi-stage builds. Overall, Multi-Stage Builds have revolutionized Docker image building by enabling reduced image size and increased speed and efficiency compared to traditional Docker image building methods.

Planning the Build Process

Before diving into building a multi-stage Docker image, it is important to first plan out the build process. This can help ensure that the final image meets all necessary requirements and runs smoothly once deployed. The first step in planning the build process is to identify the necessary stages for your specific Docker image.

This can vary depending on the software being containerized and its dependencies. For example, a web application would typically require a stage for installing dependencies, a stage for building the application, and a final stage for running it.

It is also important to consider any constraints or limitations that may impact the build process, such as limited disk space or network bandwidth. By outlining these factors early on in the planning phase, you can better optimize your build process and avoid potential issues later on.

Defining Stages and their Purposes

Once you have planned out your build process, it is time to define each stage of your multi-stage Docker image and its specific purpose. Each stage should be designed to accomplish a specific task while minimizing overhead and reducing image size.

For example, in a web application Docker image, one possible breakdown of stages could be:

  • Stage 1: Install dependencies (node packages)
  • Stage 2: Build application code using installed dependencies (using npm run-script commands etc.)
  • Stage 3: Copy built code from Stage 2 and serve it via Nginx using an optimized configuration file.

It’s worth noting that each stage should be designed with reusability in mind – meaning that each one should perform only one single logical function rather than attempting more than what is necessary.

Building Each Stage Separately

Once stages are defined, the next step is to build them separately before combining them into a final Docker image. This can be done using the basic `docker build` command, with each stage specified as its own target using the `–target` flag.

For example, to build Stage 1 from the previous example image:

docker build --target stage1 -t myapp-stage1

This will create an individual image of Stage 1 that can then be used in subsequent stages. This process should be repeated for each stage until all individual layers are built and available.

Combining Stages into a Final Docker Image

Once all stages have been built and are available as separate images, they can be combined into a final Docker image using the `FROM` keyword in your Dockerfile. For example, to combine all three stages from our earlier web application Docker image:

FROM nginx:latest COPY --from=stage1 /app /app

COPY --from=stage2 /app/build/ /usr/share/nginx/html COPY nginx.conf /etc/nginx/conf.d/default.conf

EXPOSE 80 CMD ["nginx", "-g", "daemon off;"]

In this case, we start with an Nginx base image and copy over the contents of each stage as needed using the `COPY` command. We also include an optimized Nginx configuration file before exposing port 80 and starting Nginx.

By breaking down our build process into multiple stages and building them separately before combining them into one final image, we achieve greater efficiency and optimal performance. With this approach, our resulting Docker image is smaller, faster, and more secure than traditional Docker builds.


Multi-stage builds are a powerful tool in the Docker developer’s toolbox. By breaking down the build process into smaller, more discrete stages, developers can create leaner and more efficient images.

This not only saves time and resources but also allows for greater control over the development process. Through this article, we have explored the basics of multi-stage builds and their benefits over traditional Docker image building.

We also walked through a step-by-step guide on building a multi-stage Docker image using phases. From planning the build process to combining stages into a final Docker image, developers with any level of experience in Docker can take advantage of this method.

Summary of Key Points Discussed in the Article

We learned that:

  • Multi-stage builds allow for leaner and more efficient images by breaking down the build process into smaller stages.
  • This method saves time and resources by reducing bloated images from traditional methods.
  • We walked through a step-by-step guide on building a multi-stage Docker image using phases that can be used by developers with any level of experience with Docker

The Future Implications for Software Development with Multi-Stage Builds

The use of multi-stage builds is becoming increasingly widespread in modern software development. As companies continue to embrace DevOps practices, it becomes more important to streamline development processes while maintaining high-quality software delivery.

Multi-stage builds provide a way to achieve both goals simultaneously. In addition, as companies move towards containerization as part of their infrastructure management strategy, multi-stage builds will play an even bigger role in streamlining development processes while ensuring secure delivery throughout distributed systems.

We can expect that multi-stage builds will become an increasingly important tool in the modern developer’s toolkit. As companies continue to adopt containerization, we can expect that multi-stage builds will be used more and more frequently to streamline the development process while delivering high-quality software.

Related Articles