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Learn how to effectively build Docker images from a parent directory using Jenkins without reorganizing your project structure.
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Building Docker Images from the Parent Directory with Jenkins: A Simple Guide

In modern DevOps practices, the integration of Jenkins and Docker is increasingly essential, especially when working with a monorepo structure. Many teams face challenges when their project's code organization does not align perfectly with Docker's expectations on file paths. In this post, we will address a common issue: how to build Docker images from a parent directory in Jenkins, especially when keeping specific files, like the Jenkinsfile, organized in subdirectories.

The Problem at Hand

Imagine you have a project structured as follows:

[[See Video to Reveal this Text or Code Snippet]]

Here, project1 and project2 both rely on a shared directory (shared_code). Whenever changes are made to any of these projects or the shared code, a new Docker image is supposed to be built and pushed to a Docker registry. However, Docker builds require context to be provided from the current working directory and do not naturally include files from parent directories, leading to complications when using Jenkins with Jenkinsfile located in project1 (or similar directories).

Why is this a problem?

When Jenkins attempts to perform the build using a Jenkinsfile stored in one of the subdirectories (like project1), it cannot access the needed files from the parent directory. This situation prevents Jenkins from building the Docker images effectively and restricts your directory structure organization.

The Solution

Fortunately, there is a way to configure Jenkins to build your Docker images directly from the parent directory without needing to move your Jenkinsfile. Here’s how to do it:

Step-by-Step Guide

Define a Build Stage in Your Jenkinsfile:

In your Jenkinsfile located in project1, you will need to define a build stage that can handle your Docker image creation. Below is an example of how to set it up:

[[See Video to Reveal this Text or Code Snippet]]

Explanation of the Code:

stage("Build image"): This defines a new stage in your Jenkins pipeline where the Docker image will be built.

steps: Undertake the steps defined within this block.

script: Allow the use of Groovy scripting within the pipeline.

docker.build(...): This method builds your Docker image:

project1:${env.BUILD_ID}: Creates a Docker image tagged with the build ID for version control.

-f ./project1/Dockerfile .: Specifies the Dockerfile path while using the current directory as the build context (this is key to the solution).

Benefits of This Approach

Maintains Organizational Structure: You can keep your Jenkinsfile within the subdirectory where it logically belongs while still accessing the parent directory's required files.

Automation of Builds: Whenever your code changes, Jenkins can trigger new builds seamlessly without involving manual adjustments in project structure.

Consistency: Enabling consistent image generation and deployment practices, crucial for efficient CI/CD pipelines.

Conclusion

By following the steps outlined above, you can effectively work with Docker and Jenkins in a monorepo setup without compromising your project organization. This allows for efficient build processes while maintaining a structured approach to your codebase, making your development workflow both practical and streamlined.

When working with CI/CD tools and containerization, finding creative solutions for directory-related problems can lead to more sustainable practices and less friction in your software development lifecycle.