kustomize-demo

Illustrate how to work with Kustomize overlays and components.

Summary

You can inherit Kubernetes settings with Kustomize bases and overlays. But! You can also compose Kubernetes settings with Kustomize components.

Getting started

The following procedure describes how to deployment app app to a hypothetical env1 environment on Docker Desktop on your laptop.

1. Create your Kubernetes cluster on Docker Desktop on your laptop—see mbigras/hello-kubernetes repo.

2. Get the code.

   git clone [email protected]:mbigras/kustomize-demo.git
   cd kustomize-demo
   

3. Run example.sh script.

   ./example.sh
   

   Your output should look like the following:

   $ ./example.sh
   # ...
   deployment.apps/app created
   # ...
   {
     "app": "app",
     "env": "env1",
     "color": "cheapblue",
     "password": "s3cr3t",
     "features": [
       "feature1",
       "feature2"
     ]
   }
   deployment.apps "app" deleted
   

   Observation: Notice that you created your app—that is, a app Kubernetes Deployment—, send a test request, and deleted your app!

Study Kustomize code

The following procedure describes how to create an app Kubernetes Deployment with Kustomize overlays and components.

1. Build your app Kubernetes settings for env1 environment.

   kustomize build [email protected]:mbigras/kustomize-demo.git//overlays/env1?ref=35b728e6ba9ad874fa6f49985aa5081508fcc52d
   

   Your output should look like the following:

   $ kustomize build [email protected]:mbigras/kustomize-demo.git//overlays/env1?ref=35b728e6ba9ad874fa6f49985aa5081508fcc52d
   apiVersion: apps/v1
   kind: Deployment
   metadata:
     labels:
       app: app
     name: app
   spec:
     selector:
       matchLabels:
         app: app
     template:
       metadata:
         labels:
           app: app
       spec:
         containers:
         - env:
           - name: ENV
             value: env1
           - name: COLOR
             value: cheapblue
           - name: PASSWORD
             value: s3cr3t
           - name: FEATURE2
             value: "on"
           - name: FEATURE1
             value: "on"
           image: mbigras/app:2023-07-15
           name: app
   

   Consider the following details:

   1. Observation: Notice that the app Deployment contains an app Container that is configured to run in env1 environment.
   2. Note: You inject settings as environment variables—follows excellent twelve-factor methodology—see https://12factor.net/config page.

2. To understand how the ENV, COLOR, and PASSWORD settings reach app running in env1 environment, consider the overlays/env1/kustomization.yaml#L3-L6 code.

   kind: Kustomization
   apiVersion: kustomize.config.k8s.io/v1beta1
   resources:
     - ../../base
   patches:
     - path: deployment.yaml
   # ...

   Observation: Notice how your overlay inherits your base, then patches—inheritance.

3. To understand how the FEATURE1 and FEATURE2 settings reach app running in env1 environment, consider the overlays/env1/kustomization.yaml#L7-L9 code.

   kind: Kustomization
   apiVersion: kustomize.config.k8s.io/v1beta1
   # ...
   components:
     - ../../components/feature1
     - ../../components/feature2

   Observation: Notice how your overlay reaches your components like plug and play composition—excellent!

Conclusion

You can freely compose Kubernetes YAML objects with Kustomize bases, overlays, and components. Kustomize bases and overlays compose like inheritance. Kustomize components compose like plug and play.