Dockerfile vs Buildpacks: Which One to Choose?

In the modern era of cloud computing, applications are developed in such a way that every component of an entire application, is its self-contained micro-application. For example, in the case of an e-commerce website, the cart service, the item search service, and the payment service are all individual applications that are designed to work together. These distributions of applications are beneficial as it help scale up individual components of the application as required instead of scaling every single component. This can help to efficiently manage resource allocation which ultimately helps in savings on the cloud and application hosting costs.

To seamlessly create this kind of distributed architecture and efficiently scale the applications, the application code needs to be packaged into tiny containers. Containers are a lightweight package of an application's code, configuration files, libraries, and dependencies and allow you to run the same application in different environments. Developers need to write build files to provide instructions on how to package the application code in the container. When there is an application that has multiple different components, a container build file has to be created for every component. If there are 10+ containers that require their build instructions, it can be cumbersome for developers to write, customize, and edit the files based on the requirements.

Within this blog, we will be looking at two ways of building containers. We will be exploring the traditional Dockerfile, and the new cloud-native buildpacks project and look at the key differences between both. By the end of this blog, you will understand how both Dockerfiles and buildpacks are used for creating container images, and you will be able to decide which method is best suited for your application requirements.

What is a DockerFile?

A Dockerfile is a configuration file used to define the steps required to build a Docker Image. It acts as a blueprint for building containerized images, specifying the environment, application binaries, dependencies, environment variables, secrets, and commands needed to create and run the application. A Dockerfile as a whole provides detailed instructions to the Docker Engine on the steps that need to be followed for building a container image for the specific application. You can think of a Dockerfile as a recipe for creating a delicious meal. It is a set of instructions on how a container is to be created.

How does DockerFile Work?

While writing a Dockerfile for providing the build instructions, several things have to be defined. Let’s take a look at the steps that are involved when defining the configurations for a Dockerfile.

1. Define a base image. This usually is an image containing language-specific tools such as node. 
2. Define the working directory. This will be used as the base directory after the container image is created.
3. Copy the application code into the container
4. Define the environment variables and secrets
5. Add specific commands 
6. Set the Entrypoint for the application

To optimize the size of the Docker Image, you can even create a multi-stage build. In a typical multi-stage Dockerfile build, the base image used is quite heavy as it containers a lot of dependencies. Many of the dependencies are only required for building the binary files for the application. However, once the binary is created, the dependencies are no longer required. They are simply bloating the container image. The created binary is copied to the second stage of the Docker build process. In the second stage, you can use a lightweight base image such as alpine which only has the OS dependencies. This new lightweight image will only be a few megabytes in size which makes it easier to download the image and run it in different environments.

Once the Dockerfile is written the docker build command is used to process the Dockerfile and build the Docker Image. This image can then be run across different environments. Once the Docker image is built, the image can be pushed and stored in OCI-compliant container registries like DockerHub or private repositories, making it easy to share the image and run the container image. 

The below file shows an example of how a DockerFile is written. The below Dockerfile shows how to build a Go application in a single-stage build. There are comments included, explaining what each step is doing.

FROM golang:1.21.3-alpine # Select the base image for the container image

WORKDIR /app # Set the working directory

COPY go.mod go.sum ./ # Copy the files defining the Go dependencies to the working directory container 

COPY ./app ./ # Copy the code in the ./app directory to the working directory in the container

RUN go mod download # Download the golang dependencies

RUN go build -o gin-server # Trigger the build process for the Go Application

EXPOSE 9000 # Expose the container on port 9000

ENTRYPOINT [ "/app/gin-server" ] # Execute the specified binary file to run the application in the container

When writing a DockerFile, you may need to use the CMD and ENTRYPOINT instructions quite a bit. It can be confusing to know when to use CMD and when to use ENTRYPOINT. To learn about Docker Entrypoint and Docker CMD, please read this blog.

Benefits of a DockerFile

Using a Dockerfile has several benefits. Let’s understand what are some of the key benefits of using a DockerFile for building container images.

• Fine-Grained Control: A Dockerfile gives developers complete control over the container image creation process. It allows precise customization of the operating system, libraries, dependencies, application binaries, and configuration. This control ensures that the image matches the exact requirements of the application, providing flexibility for complex use cases or unique runtime environments.
• Transparency and Reproducibility: Every step of the image-building process is explicitly defined in the Dockerfile, making it easy to understand, audit, and reproduce. Teams can track changes over time through version control, ensuring consistency across development, testing, and production environments.
• Customizability: Developers can craft Dockerfiles tailored to specific applications or workflows. Whether optimizing for image size, security, or runtime performance, Dockerfiles allows teams to adapt images to meet project goals.
• Community and Ecosystem Support: Dockerfiles leverage a vast library of base images and community-shared best practices. Developers can start with a pre-built base image, modify it as needed, and benefit from a well-established ecosystem that includes tools, guides, and examples.
• Efficient Caching: Dockerfile instructions are layered, enabling Docker to cache previous steps. This significantly speeds up iterative builds, as unchanged layers don’t need to be rebuilt. This efficiency is especially valuable in CI/CD pipelines.
• Integration with DevOps Workflows: Dockerfiles integrate seamlessly into existing DevOps workflows, allowing teams to automate image builds, enforce best practices, and share standardized artifacts across teams and environments.

What are Buildpacks?

Buildpacks simplifies the process of creating container images by automatically converting your source code into runnable application images. Buildpakcs analyzes your code, determines the required runtime and dependencies, and then assembles everything into a standardized container image without needing you to write a Dockerfile. This automation saves time and enforces best practices for building secure and efficient container images.

Think of buildpacks like skilled bakers in a modern bakery. You provide the raw ingredients, and the bakers figure out the recipe, prepare the dough, bake it to perfection, and package the final product. Instead of micromanaging the process and defining every single step of the process as done in a Dockerfile, buildpacks only require the base code, and it will automatically figure out how to create the correct container image while ensuring best practices are followed. To learn more about Buildpacks, please check out this blog.

In a cloud-native environment, this approach is beneficial as it simplifies workflows, ensures consistent builds across teams, and keeps your application up-to-date with the latest runtime and security patches. By using buildpacks, developers can focus on creating and improving applications rather than worrying about the mechanics of building and deploying them

How do Buildpacks work?

Buildpacks work through a series of automated steps that transform your source code into a container image. The process typically consists of three primary stages: Detection, Build, and Export. Each stage is handled by a set of modular and reusable scripts provided by the buildpack.

1. Detection

In this stage, buildpacks analyze your source code to identify the type of application and its requirements. For example, if your code contains a package.json, the buildpack detects it as a Node.js application. Similarly, a requirements.txt might indicate a Python application. Buildpacks use these detection rules to determine whether they can support the application. If multiple buildpacks are available, they can work together, chaining their capabilities.

2. Build

Once the detection is successful, the buildpacks construct the application image. This involves:

• Fetching Dependencies: The buildpack downloads necessary libraries and frameworks defined in your code's configuration files.
• Setting Up Environment: It configures the runtime environment to meet the application's needs such as installing the correct Python and PIP version for a Python application.
• Optimizing: Buildpacks may perform optimizations, such as reducing image size by excluding unnecessary files or creating efficient caching layers. Similar to a multi-stage Dockerfile

3. Export

The export stage involves packaging the application into a standardized container image. This image includes the application, its dependencies, and runtime configurations. The image is then ready to be deployed to any container platform, such as Kubernetes.

Benefits of Buildpacks

Cloud Native Buildpacks offer several advantages, particularly for modern application development and deployment in cloud environments. Here are the key benefits:

• Simplification and Automation: Buildpacks automate the process of transforming source code into container images. Developers don’t need to write complex Dockerfiles or manually configure build instructions. This simplicity reduces the learning curve and ensures that the build process is consistent and repeatable across different teams and environments.
• Standardized and Secure Builds: Buildpacks produce OCI-compliant container images by following well-defined conventions. This standardization ensures compatibility with any container runtime or orchestration platform, such as Kubernetes. Additionally, buildpacks include security features like regular updates to base images and dependencies and follow best practices for configurations, reducing vulnerabilities in the resulting container images.
• Language and Framework Awareness: Buildpacks can detect the type of application such as Java, Node, or Python, and automatically fetch the required runtime and dependencies. This eliminates the need for developers to manually configure environment setups, ensuring that applications run optimally in production.
• Enhanced Developer Productivity: With less time spent on image configuration and dependency management, developers can focus on writing code and delivering features. Buildpacks also integrate seamlessly with platforms like Kubernetes, enabling smooth workflows.
•  Support for Multi-Buildpack Scenarios: Applications with multiple components or dependencies can benefit from chaining buildpacks. For example, one buildpack can handle the Node.js front end, while another manages a Python-based back end. This modular approach adds flexibility to handle complex applications.

Differences between Dockerfile and Buildpacks

Dockerfiles and Buildpacks are both methods to build container images, but they cater to different needs and levels of abstraction. A Dockerfile is a step-by-step script written by developers that specifies exactly how an image is built. It gives fine-grained control over the process, from selecting a base image to defining environment variables and copying files. This makes Dockerfiles ideal for developers who need customization and complete transparency in their image-building process.

Buildpacks, on the other hand, abstract away much of the complexity. They automatically detect the application’s type, fetch the necessary dependencies, and configure the environment without requiring developers to write a custom script. While this makes Buildpacks developer-friendly and fast for most standard use cases, they trade off some flexibility for simplicity.

Dockerfiles shine in scenarios where customization is paramount. For example, if you need to install non-standard libraries, apply custom patches, or use experimental base images, a Dockerfile gives you full control. Dockerfiles are also better for unconventional applications or those written in languages not supported by Buildpacks.

Buildpacks excel in productivity and simplicity, especially for standard web applications and in organizations adopting DevOps and cloud-native practices. They enforce best practices and produce lightweight, secure images with minimal configuration, making them ideal for developers who want to focus on code rather than infrastructure.

Dockerfiles are still paramount and required in certain scenarios such as:

• Highly Custom Applications: When you need fine-grained control over every step in the image-building process.
• Legacy or Unsupported Languages: If your application uses a language or framework that Buildpacks doesn’t support.
• Non-Standard Requirements: When you need to include custom dependencies, third-party libraries, or unique configurations.

Building Dockerfiles & Buildpacks in Devtron

Devtron is an open-source platform to simplify all your Kubernetes operations right from the build process, to deployments and managing Day 2 operations. With Devtron, you can abstract a lot of the complexities of Kubernetes and it can help you boost your DevOps efficiency.

During the build process, there needs to be a way for building the container image, before you can deploy the application. Devtron’s CI pipeline can help you to create the container image using either Docker Images or by using Buildpacks. Let’s take a look at how Devtron simplifies the container creation process.

Dockerfile

Devtron can let you create images using Dockerfiles in two ways. If you already have written a Dockerfile for your application, you can use the existing Dockerfile. All you have to do is pass the path to the Dockerfile in the Git repository.

If you do not have the Dockerfile, Devtron lets you create it within the platform’s UI. You can write your own custom Dockerfile specific to your application. Devtron also provides a couple of different Dockerfile templates for a number of popular languages and frameworks. In most cases, you can use the template as is, and will only need to plug in the application-specific environment variables.

Devtron also provides some additional features that are useful when building the container image. The UI provides an advanced option to select the target build platform such as ARM or x86. You can also define the Docker build arguments.

Buildpacks

Devtron also lets you select Buildpacks for building the container image. So you can select your preferred method for building the container image as per your application requirements. The Buildpacks approach will automatically detect the language used for the application, and you can select the buildpack version.

Similar to the Docker build arguments, you can also pass in arguments for the build environment for buildpacks. 

Conclusion

In conclusion, both Dockerfiles and Buildpacks offer distinct advantages, catering to different needs for containerization. Dockerfiles provide granular control, allowing developers to customize every aspect of their container images, making them ideal for complex applications with specific build requirements or when working with less common tech stacks. On the other hand, Buildpacks shine in simplifying the development process, automating best practices, and fostering consistency across teams, making them a great choice for standard applications, especially in environments prioritizing developer productivity and scalability.

Choosing between Dockerfiles and Buildpacks depends on your project's requirements. If you need complete control over the image creation process, Dockerfiles are your go-to solution. However, if you value automation, consistency, and ease of use, Buildpacks can streamline your workflow. Ultimately, the decision comes down to balancing flexibility with simplicity and aligning the choice with your team’s expertise and project needs.