Build a Container Image Inside a K8s Cluster

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Build a Container Image Inside a K8s Cluster

Take a look at how you can build a container image inside Kubernetes without using the Docker daemon through Google's Kaniko.

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Learn how to build a source into a container image from a Dockerfile inside a Kubernetes cluster and push the image to IBM Cloud Container Registry; all of this using Google’s Kaniko tool.

So, What is Kaniko?

Kaniko is a tool to build container images from a Dockerfile, inside a container or Kubernetes cluster.

If you don’t have a Kubernetes cluster with Knative and Istio installed, it’s recommended to follow the instructions mentioned in my previous post that also introduces you to the components of Knative —  Install Knative with Istio and deploy an app on IBM Cloud

This tutorial uses the Build and Serving components of Knative to orchestrate an end-to-end deployment.

A Knative build extends Kubernetes and utilizes existing Kubernetes primitives to provide you with the ability to run on-cluster container builds from source. For example, you can write a build that uses Kubernetes-native resources to obtain your source code from a repository, build it into container a image, and then run that image.

Knative Serving builds on Kubernetes and Istio to support deploying and serving of serverless applications and functions. Serving is easy to get started with and scales to support advanced scenarios.

What is a Build Template?

A BuildTemplateis one of the key features of Knative build used to define reusable templates and encapsulates a shareable build process with some limited parameterization capabilities. A set of curated and supported build templates is available in the build-templates repo. We will be using the Kaniko BuildTemplate in the tutorial.

Kaniko doesn’t depend on a Docker daemon and executes each command within a Dockerfile completely in userspace. This enables building container images in environments that can’t easily or securely run a Docker daemon, such as a standard Kubernetes cluster.

Let’s start by creating a Kaniko BuildTemplate and saving this as kaniko.yaml

apiVersion: build.knative.dev/v1alpha1
kind: BuildTemplate
  name: kaniko
  - name: IMAGE
    description: registry.<region>.bluemix.net/<namespace>/knative-node-kaniko #replace <region> and <namespace>
  - name: DOCKERFILE
    description: ./Dockerfile
    default: /workspace/Dockerfile

  - name: build-and-push
    image: gcr.io/kaniko-project/executor
    - --dockerfile=${DOCKERFILE}
    - --destination=${IMAGE}


  •  IMAGE : The Docker image name to apply to the newly built image. Replace <region>and <namespace> with appropriate values. Remember these values as you have to replace these values in the YAMLscripts below.
  •  DOCKERFILE : The path to the Dockerfile to execute (default:./Dockerfile).
Note: To check your region, run ibmcloud cr regionand to setup a new namespace, refer this link

If you are looking for a sample with Dockerfile, YAML templates and scripts, Clone this repository

git clone  https://github.com/VidyasagarMSC/knative-deploy

and refer the Kaniko folder. 

Kaniko builds an image and pushes it to the destination defined as a parameter. In order to properly authenticate to the remote container registry (IBM Cloud Container Registry), the build needs to have the proper credentials. This is achieved using a build ServiceAccount.

Before this, let’s define a Secret containing the username and password that the build should use to authenticate (basic) to IBM Cloud Container Registry:

apiVersion: v1
kind: Secret
  name: basic-user-pass
    build.knative.dev/docker-0: registry.<region>.bluemix.net # replace the <region>
type: kubernetes.io/basic-auth
  username: token # username
  password: <password> # token-value

For <password>, run the below command

$ ibmcloud cr token-add --description “This is a token” --non-expiring --readwrite

Token identifier 58669dd6–3ddd-5c78–99f9-ad0a5aabd9ad 
Token            <token_value>
Use the returned token_value as your password and save the file as secret.yaml . For more details related to token, refer this link

Now you can create aserviceaccount.yaml file with the ServiceAccountusing the secret as shown below

apiVersion: v1
kind: ServiceAccount
  name: build-bot
- name: basic-user-pass

Let’s use ServiceAccount in our Build and save the file asbuild.yaml

apiVersion: build.knative.dev/v1alpha1
kind: Build
  name: kaniko-build
  serviceAccountName: build-bot
      url: https://github.com/VidyasagarMSC/knative-deploy # source code from GitHub
      revision: master
    name: kaniko
    - name: IMAGE
      value: registry.<region>.bluemix.net/<namespace>/knative-node-kaniko # replace <region> and <namespace>

Execute the build

$ kubectl apply --filename kaniko.yaml
$ kubectl apply --filename secret.yaml
$ kubectl apply --filename serviceaccount.yaml
$ kubectl apply --filename build.yaml

The build should have been kicked off. Let’s take a look.

Runningkubectl get pods , you should see a pod named kaniko-build with a postfix (say XXXXX).

For logs, run this command

$ kubectl logs kanika-build-XXXXX -c build-step-build-and-push

If everything runs as expected, you should see the image in the list when you run the below command

$ ibmcloud cr images

Hurray!! you have just created a container image without a Docker Daemon. Let’s deploy and serve the app so that we can access it from anywhere. For this, lets create a service.yaml file:

apiVersion: serving.knative.dev/v1alpha1 # Current version of Knative
kind: Service
  name: knative-node-kaniko # The name of the app
  namespace: default # The namespace the app will use
            image: registry.<region>.bluemix.net/<namespace>/knative-node-kaniko # The URL to the image of the app on IBMCLOUD Registry
            - name: TARGET # The environment variable printed out by the sample app
              value: "Kaniko Node App running on IBM Cloud"

Execute the service:

$ kubectl apply --filename service.yaml

To find the IP address for your service, use kubectl get svc knative-ingressgateway -n istio-system to get the ingress IP for your cluster. If your cluster is new, it may take some time for the service to get assigned an external IP address.

$ export IP_ADDRESS=$(kubectl get svc knative-ingressgateway --namespace istio-system --output 'jsonpath={.status.loadBalancer.ingress[0].ip}')

To find the URL for your service, use

kubectl get services.serving.knative.dev knative-node-app --output jsonpath='{.status.domain}'

$ export HOST_URL=$(kubectl get services.serving.knative.dev knative-node-kaniko  --output jsonpath='{.status.domain}')

Now you can make a request to your app to see the result.

$ curl -H "Host: ${HOST_URL}" http://${IP_ADDRESS}
Response: Kaniko Node App running on IBM Cloud

Clean Up

Run the below command to remove the sample app from your cluster:

$ kubectl delete --filename service.yaml

To delete other secret,ServiceAccount and Build

$ kubectl delete --filename build.yaml
$ kubectl delete --filename serviceaccount.yaml
$ kubectl delete --filename secret.yaml
$ kubectl delete --filename kaniko.yaml

To delete the cluster (removes everything), enter the following command:

$ ibmcloud cs cluster-rm $CLUSTER_NAME
cloud, container images, docker, istio, knative, kubernetes, serverless, tutorial

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