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Ajeet Raina Docker Captain, ARM Innovator & Docker Bangalore Community Leader.

Dagger: The Programmable CI/CD Engine That Runs Pipelines in Containers

5 min read

Continuous Integration and Continuous Delivery/Deployment (CI/CD) are critical to the success of modern software development. They help to ensure that code changes are tested and deployed automatically, quickly, and efficiently. In recent years, containerization has become an essential part of CI/CD pipelines, as it provides a consistent and isolated environment to build, test, and deploy applications. In this blog post, we will explore Dagger, a programmable CI/CD engine that runs pipelines in containers. We will discuss what Dagger is, the problems it solves, and some code snippets to get you started.

What is Dagger?

Dagger is a CI/CD engine that allows you to run your pipelines in containers. It was built by Solomon Hykes, the founder of Docker, with the goal of making CI/CD pipelines more reliable and efficient. Dagger uses containerization to provide a consistent and isolated environment for building, testing, and deploying applications. It is designed to be programmable, so you can customize your pipelines to fit your specific needs.

Dagger is open-source and written in Go. It works by defining pipelines in YAML files, which are then executed by Dagger. You can use Docker images for your pipeline steps, or you can create custom images with the tools and dependencies you need. Dagger supports multiple languages, including Python, Node.js, and Go, and it can run on various operating systems, including Linux, macOS, and Windows.

What Problem does Dagger Solve?

Dagger solves several problems that are common in CI/CD pipelines, including:

Environment Consistency

One of the biggest challenges of CI/CD is ensuring that the environment in which your code runs is consistent across different stages of the pipeline. Dagger uses containers to provide a consistent environment for each stage of the pipeline, which helps to reduce the risk of issues related to environment inconsistencies.

Dependency Management

Managing dependencies can be time-consuming and error-prone. Dagger uses Docker images to manage dependencies, which makes it easier to create and maintain consistent environments for each pipeline stage.


Dagger is designed to be scalable, which means it can handle pipelines of any size. It can run multiple pipelines simultaneously, and it can scale up or down based on demand.


Dagger is programmable, which means you can customize your pipelines to fit your specific needs. You can define custom steps, use custom Docker images, and add your own scripts and tools.

How does Dagger work?


  • Your program imports the Dagger SDK in your language of choice.
  • Using the SDK, your program opens a new session to a Dagger Engine: either by connecting to an existing engine, or by provisioning one on-the-fly.
  • Using the SDK, your program prepares API requests describing pipelines to run, then sends them to the engine. The wire protocol used to communicate with the engine is private and not yet documented, but this will change in the future. For now, the SDK is the only documented API available to your program.
  • When the engine receives an API request, it computes a Directed Acyclic Graph (DAG) of low-level operations required to compute the result, and starts processing operations concurrently.
  • When all operations in the pipeline have been resolved, the engine sends the pipeline result back to your program.
  • Your program may use the pipeline’s result as input to new pipelines.

Getting Started

Now that we have discussed what Dagger is and the problems it solves, let’s take a look at some code snippets to get you started. In this example, we will create a pipeline that builds a Node.js application, tests it, and deploys it to a remote server.

Installing Dagger on Docker Desktop

Installing Dagger on Docker Desktop is a straightforward process. Here are the steps to follow:

Download the Dagger binary

Go to the Dagger releases page on GitHub ( and download the latest Dagger binary for your operating system.

For Docker Desktop on macOS or Windows, download the dagger-darwin or dagger-windows binary, respectively.


Add the Dagger binary to your PATH

After downloading the Dagger binary, you need to add it to your PATH so that you can run the Dagger command from the terminal. To do this, you can copy the binary to a directory in your PATH, such as /usr/local/bin on macOS or %USERPROFILE%\bin on Windows.

mv dagger /usr/local/bin/dagger

Verify the installation

After adding the Dagger binary to your PATH, you can verify that it’s installed correctly by running the following command in your terminal:

dagger version
dagger 0.4.1 darwin/arm64

This command should print the version of Dagger that you installed.

Once you have Dagger installed, you can define and run pipelines using YAML files. To get started with Dagger, you can refer to the official Dagger documentation, which provides detailed information on how to create and run pipelines.

First, let’s define our pipeline in a YAML file:

image: node:latest

  - name: Install Dependencies
    run: npm install
  - name: Run Tests
    run: npm test
  - name: Deploy
    run: |
      ssh user@remote-server 'cd /path/to/app && git pull origin master && npm install && pm2 restart app'

In this example, we are using the latest Node.js image as our base image. We then define three steps: install dependencies, run tests, and deploy. In the deploy step, we use SSH to connect to a remote server and restart the application using PM2.

To execute this pipeline, we can use the following command:

dagger run my-pipeline.yaml

This will start the pipeline and execute each step in order. Dagger will use a Docker container to run each step, which ensures environment consistency and makes it easier to manage dependencies.

A Simple CI/CD Pipeline for NodeJS Developers

Here’s an example Dagger YAML file that defines a simple CI/CD pipeline for a Node.js application:

version: '1.0'

  IMAGE_NAME: my-node-app

  - name: clone
    image: alpine/git
      - git clone

  - name: install
    image: node:14
      - cd my-node-app
      - npm install

  - name: test
    image: node:14
      - cd my-node-app
      - npm test

  - name: build
    image: node:14
      - cd my-node-app
      - npm run build
      - docker build -t $IMAGE_NAME .

  - name: push
    image: docker
      - docker login -u $DOCKER_USERNAME -p $DOCKER_PASSWORD

  - name: deploy
    image: kubectl
      - kubectl apply -f kubernetes/deployment.yaml

This Dagger YAML file defines a pipeline with six steps:

  • Clone: Clones the repository from GitHub.
  • Install: Installs Node.js dependencies using the npm install command.
  • Test: Runs unit tests using the npm test command.
  • Build: Builds a Docker image for the Node.js application using the docker build command.
  • Push: Tags and pushes the Docker image to a container registry using the docker tag and docker push commands.
  • Deploy: Deploys the Docker image to a Kubernetes cluster using the kubectl apply command.

This is just a simple example, but it shows how you can use Dagger to define a CI/CD pipeline for a Node.js application in a few lines of code. The image field specifies the Docker image used for each step, and the commands field specifies the commands to be run in the container. You can also use variables to define environment variables that can be used across the pipeline.


Dagger is a powerful CI/CD engine that uses containerization to provide a consistent and isolated environment for building, testing, and deploying applications. It solves several common problems in CI/CD, including environment consistency, dependency management, scalability, and customizability. With Dagger, you can define pipelines in YAML files, use Docker images for your pipeline steps, and customize your pipelines to fit your specific needs.

In this blog post, we looked at an example pipeline that builds, tests, and deploys a Node.js application using Dagger. However, Dagger is not limited to Node.js applications and can be used with multiple languages and operating systems. If you are interested in trying Dagger for your CI/CD pipelines, you can find more information and documentation on the official Dagger website and GitHub repository.

Overall, Dagger is a valuable tool for modern software development, as it provides a reliable and efficient way to build, test, and deploy applications. Its containerization approach ensures environment consistency, making it easier to manage dependencies and scale pipelines as needed. By using Dagger, you can focus on developing and delivering high-quality software without worrying about the complexities of managing your CI/CD pipelines.

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Ajeet Raina Docker Captain, ARM Innovator & Docker Bangalore Community Leader.

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