Using custom run image for CNB builder

Introduction

What is CNB?

Cloud Native Buildpacks (CNB) enable building a container image from source code without the need for a Dockerfile. Skaffold supports building with CNB, requiring only a local Docker daemon.

CNB uses two images when building an application image:

• A run image serves as the base image for the resulting application image.
• A build image acts as the host for performing the build.

What you'll learn

• how to annotate an arbitrary image and use it as a CNB run image.
• how to integrate the custom run image with a sample Buildpacks application using Skaffold's artifact dependencies feature.

Time to complete: <walkthrough-tutorial-duration duration=10></walkthrough-tutorial-duration>

Click the Start button to move to the next step.

First steps

Start a Minikube cluster

We'll use minikube as our local kubernetes cluster of choice.

Run:

minikube start

Write a custom CNB run image

CNB run and build images require some additional metadata to identify the Stack ID and user/group accounts to be used. A stack is a specification or contract. For example, the io.buildpacks.stacks.bionic stack defines that it provides the same packages as installed on Ubuntu 18.04.

We add a base artifact with a single <walkthrough-editor-open-file filePath="base/Dockerfile">Dockerfile</walkthrough-editor-open-file> that defines the required metadata, and reference this as an <walkthrough-editor-select-line filePath="skaffold.yaml" startLine="4" startCharacterOffset="4" endLine="6" endCharacterOffset="0">artifact</walkthrough-editor-select-line> called base in our skaffold.yaml.

Next we'll use this artifact as the run image for a sample Buildpacks app.

Use it in a sample Buildpacks app

We use a simple <walkthrough-editor-open-file filePath="app/main.go">Go application</walkthrough-editor-open-file> and reference it as an <walkthrough-editor-select-line filePath="skaffold.yaml" startLine="6" startCharacterOffset="4" endLine="8" endCharacterOffset="0">artifact</walkthrough-editor-select-line> called app in our skaffold.yaml.

To use the base artifact as the custom run image we:

• add an <walkthrough-editor-select-line filePath="skaffold.yaml" startLine="13" startCharacterOffset="4" endLine="15" endCharacterOffset="0">artifact dependency</walkthrough-editor-select-line> for app artifact on the base artifact.
• set the <walkthrough-editor-select-line filePath="skaffold.yaml" startLine="10" startCharacterOffset="6" endLine="11" endCharacterOffset="0">runImage</walkthrough-editor-select-line> property of the app artifact to be the base artifact.

Run it!

Run this command and Skaffold should take care of building the artifacts in order and deploying the provided <walkthrough-editor-open-file filePath="k8s/web.yaml">manifest</walkthrough-editor-open-file>.

skaffold dev --port-forward

Once the image has been built and deployed click on the <walkthrough-web-preview-icon></walkthrough-web-preview-icon> icon and select Preview on port 8080. This should redirect to the running service and show the output:

Hello, World!

The Go app reads <walkthrough-editor-open-file filePath="base/hello.txt">hello.txt</walkthrough-editor-open-file> that's provided by the base artifact. Lets change the text from <walkthrough-editor-select-line filePath="base/hello.txt" startLine="0" startCharacterOffset="0" endLine="1" endCharacterOffset="0">Hello, World!</walkthrough-editor-select-line> to Hello, Buildpacks!. This should trigger a rebuild of the base artifact which in turn triggers a rebuild and redeploy for the app artifact. Once that completes click on the <walkthrough-web-preview-icon></walkthrough-web-preview-icon> icon again and select Preview on port 8080. This should redirect to the running service and show the output:

Hello, Buildpacks!

Congratulations

<walkthrough-conclusion-trophy></walkthrough-conclusion-trophy>

All done!

You now know how to use Buildpacks with custom run images and use Skaffold to tie the loop together.