k8s-simple-app-example

Example repo shows how to use tools from carvel dev: ytt, kbld, kapp and kwt to work with a simple Go app on Kubernetes.

Associated blog post: Deploying Kubernetes Applications with ytt, kbld, and kapp.

Install Carvel Tools

Head over to carvel.dev for installation instructions.

Deploying Application

Each top level step has an associated config-step-* directory. Refer to Directory Layout for details about files.

Step 1: Deploying application

Introduces kapp for deploying k8s resources.

kapp deploy -a simple-app -f config-step-1-minimal/
kapp inspect -a simple-app --tree
kapp logs -f -a simple-app

Step 1a: Viewing application

Once deployed successfully, you can access frontend service at 127.0.0.1:8080 in your browser via kubectl port-forward command:

kubectl port-forward svc/simple-app 8080:80

You will have to restart port forward command after making any changes as pods are recreated. Alternatively consider using kwt which exposes cluser IP subnets and cluster DNS to your machine and does not require any restarts:

sudo -E kwt net start

and open http://simple-app.default.svc.cluster.local/.

Step 1b: Modifying application configuration

Modify HELLO_MSG environment value from stranger to something else in config-step-1-minimal/config.yml, and run:

kapp deploy -a simple-app -f config-step-1-minimal/ --diff-changes

In following steps we'll use -c shorthand for --diff-changes.

Step 2: Configuration templating

Introduces ytt templating for more flexible configuration.

kapp deploy -a simple-app -c -f <(ytt -f config-step-2-template/)

ytt provides a way to configure data values from command line as well:

kapp deploy -a simple-app -c -f <(ytt -f config-step-2-template/ -v hello_msg=another-stranger)

New message should be returned from the app in the browser.

Step 2a: Configuration patching

Introduces ytt overlays to patch configuration without modifying original config.yml.

kapp deploy -a simple-app -c -f <(ytt -f config-step-2-template/ -f config-step-2a-overlays/custom-scale.yml)

Step 2b: Customizing configuration data values per environment

Requires ytt v0.13.0+.

Introduces use of multiple data values to show layering of configuration for different environment without modifying default values.yml.

kapp deploy -a simple-app -c -f <(ytt -f config-step-2-template/ -f config-step-2b-multiple-data-values/)

Step 3: Building container images locally

Introduces kbld functionality for building images from source code. This step requires Minikube. If Minikube is not available, skip to the next step.

eval $(minikube docker-env)
kapp deploy -a simple-app -c -f <(ytt -f config-step-3-build-local/ | kbld -f-)

Note that rerunning above command again should be a noop, given that nothing has changed.

Step 3a: Modifying application source code

Uncomment fmt.Fprintf(w, "<p>local change</p>") line in app.go, and re-run above command:

kapp deploy -a simple-app -c -f <(ytt -f config-step-3-build-local/ | kbld -f-)

Observe that new container was built, and deployed. This change should be returned from the app in the browser.

Step 4: Building and pushing container images to registry

Introduces kbld functionality to push to remote registries. This step can work with Minikube or any remote cluster.

docker login -u dkalinin -p ...
kapp deploy -a simple-app -c -f <(ytt -f config-step-4-build-and-push/ -v push_images_repo=gcr.io/projectX/k8s-simple-app | kbld -f-)

Step 5: Clean up cluster resources

kapp delete -a simple-app

There is currently no functionality in kbld to remove pushed images from registry.

Directory Layout

• app.go: simple Go HTTP server
• Dockerfile: Dockerfile to build Go app
• config-step-1-minimal/
  • config.yml: basic k8s Service and Deployment configuration for the app
• config-step-2-template/
  • config.yml: slightly modified configuration to use ytt features, such as data module and functions
  • values.yml: defines extracted data values used in config.yml
• config-step-2a-overlays/
  • custom-scale.yml: ytt overlay to set number of deployment replicas to 3
• config-step-3-build-local/
  • build.yml: tells kbld about how to build container image from source (app.go + Dockerfile)
  • config.yml: same as prev step
  • values.yml: same as prev step
• config-step-4-build-and-push/
  • build.yml: same as prev step
  • push.yml: tells kbld about how to push container image to remote registry
  • config.yml: same as prev step
  • values.yml: defines shared configuration, including configuration for pushing container images

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