4. Checkpoint

4. Checkpoint: Check custom resource and codes

4.1. Overview

1. Create CustomResourceDefinition foos.example.com.
2. Create Foo object.
3. Read the Foo object from main.go.

4.2. Implement

1. Create main.go.

   package main
   
   func main() {
   
   }
   

2. Init k8s.io/klog/v2

   import (
       "k8s.io/klog/v2"
   )
   

   klog.InitFlags(nil)
   

3. Set kubeconfig from flag.

   If home is detected, use ~/.kube/config as default, otherwise, -kubeconfig argument is required.

   import (
       "flag"
       "path/filepath"
       ...
       "k8s.io/client-go/util/homedir"
   )
   

   var kubeconfig *string
   if home := homedir.HomeDir(); home != "" {
       kubeconfig = flag.String("kubeconfig", filepath.Join(home, ".kube", "config"), "(optional)")
   } else {
       kubeconfig = flag.String("kubeconfig", "", "absolute path to kubeconfig file")
   }
   flag.Parse()
   

4. Set config for Kubernetes client with client-go/tools/clientcmd

   config is *restclient.Config

   import (
       ...
       "k8s.io/client-go/tools/clientcmd"
   )
   

   config, err := clientcmd.BuildConfigFromFlags("", *kubeconfig)
   if err != nil {
       klog.Fatalf("Error building kubeconfig: %s", err.Error())
       klog.FlushAndExit(klog.ExitFlushTimeout, 1)
   }
   

5. Initialize clientset for our custom resource.

   import (
       clientset "github.com/nakamasato/sample-controller/pkg/generated/clientset/versioned"
   )
   

   exampleClient, err := clientset.NewForConfig(config)
   if err != nil {
       klog.Fatalf("Error building example clientset: %s", err.Error())
       klog.FlushAndExit(klog.ExitFlushTimeout, 1)
   }
   

6. List the custom resource Foo.

   import (
       "context"
       metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
   )
   

   foos, err := exampleClient.ExampleV1alpha1().Foos("").List(context.Background(), metav1.ListOptions{})
   if err != nil {
       klog.Fatalf("listing foos %s %s", err.Error())
       klog.FlushAndExit(klog.ExitFlushTimeout, 1)
   }
   klog.Infof("length of foos is %d", len(foos.Items))
   

Final main.go:

package main

import (
    "context"
    "flag"
    "path/filepath"

    "k8s.io/client-go/tools/clientcmd"
    "k8s.io/client-go/util/homedir"
    "k8s.io/klog/v2"

    clientset "github.com/nakamasato/sample-controller/pkg/generated/clientset/versioned"
    metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
)

func main() {
    klog.InitFlags(nil)

    var kubeconfig *string
    if home := homedir.HomeDir(); home != "" {
        kubeconfig = flag.String("kubeconfig", filepath.Join(home, ".kube", "config"), "(optional)")
    } else {
        kubeconfig = flag.String("kubeconfig", "", "absolute path to kubeconfig file")
    }
    flag.Parse()

    config, err := clientcmd.BuildConfigFromFlags("", *kubeconfig)
    if err != nil {
        klog.Fatalf("Error building kubeconfig: %s", err.Error())
        klog.FlushAndExit(klog.ExitFlushTimeout, 1)
    }

    exampleClient, err := clientset.NewForConfig(config)
    if err != nil {
        klog.Fatalf("Error building example clientset: %s", err.Error())
        klog.FlushAndExit(klog.ExitFlushTimeout, 1)
    }

    foos, err := exampleClient.ExampleV1alpha1().Foos("").List(context.Background(), metav1.ListOptions{})
    if err != nil {
        klog.Fatalf("listing foos %s %s", err.Error())
        klog.FlushAndExit(klog.ExitFlushTimeout, 1)
    }
    klog.Infof("length of foos is %d", len(foos.Items))
}

4.3. Run and check

1. Build sample-controller

   go mod tidy
   go build
   

2. Register the CRD.

   kubectl apply -f config/crd/foos.yaml
   

3. Run sample-controller.

   ./sample-controller
   

   Result: no Foo exists

   length of foos is 0
   

4. Create sample foo (custom resource) with config/sample/foo.yaml.

   apiVersion: example.com/v1alpha1
   kind: Foo
   metadata:
       name: foo-sample
   spec:
       deploymentName: foo-sample
       replicas: 1
   

   kubectl apply -f config/sample/foo.yaml
   

5. Run the controller again.

   ./sample-controller
   length of foos is 1
   

6. Clean up Foo (custom resource).

   kubectl delete -f config/sample/foo.yaml