📝 Automating Builds in OpenShift: BuildConfig & ImageStreams Explained

1. Introduction

OpenShift automates container builds using two key resources: BuildConfig and ImageStreams.
Together, they provide a powerful CI/CD workflow that automatically rebuilds and deploys images whenever source code or base images change. This enables development teams to achieve seamless, automated build pipelines without external tools.

2. 🏗️ What Is BuildConfig?

A BuildConfig (BC) is a custom OpenShift resource that defines how an image should be built from source.

🔧 Key Build Strategies

• Source-to-Image (S2I) — Converts source code into an image using language-specific builders

• Docker Build — Builds using a Dockerfile

• Custom Build — Allows defining your own builder logic

📄 Sample BuildConfig YAML

This BuildConfig automatically builds a new NodeJS app image whenever the Git repository changes.

3. 🖼️ What Is an ImageStream?

An ImageStream (IS) tracks changes to images and can trigger builds or deployments accordingly.

✨ Benefits of ImageStreams

• Decouples image tags from external registries

• Enables automatic rebuilds when base images update

• Integrates tightly with BuildConfig and DeploymentConfig

📌 Trigger Example

This tells OpenShift to automatically rebuild/redeploy when the associated image changes.

4. 🔄 Workflow Overview

Here’s how the BuildConfig + ImageStream automation works:

1. Developer pushes code to Git.

2. ImageStream detects the updated image tag or Git change.

3. BuildConfig triggers a new build.

4. A new image is created and stored in the internal registry.

5. DeploymentConfig or Deployment updates automatically.

This forms the core of OpenShift’s native CI/CD pipeline.

5. 🧪 Troubleshooting Tips

Check build logs

Inspect ImageStream status

Validate triggers in BuildConfig

6. ✅ Best Practices

✔️ Use S2I for language-based applications
✔️ Tag images cleanly (:dev, :stage, :prod)
✔️ Secure Git credentials using Secrets
✔️ Enable ImageChange triggers for auto-build workflows
✔️ Use Webhooks for instant build triggers from GitHub/GitLab