028 Project 28: Kubernetes Rollout Checker

028 Build a Kubernetes Rollout Checker

Check if a Deployment is fully rolled out.

Full `main.go`

package main

import (
    "context"
    "flag"
    "fmt"
    "os"

    metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
    "k8s.io/client-go/kubernetes"
    "k8s.io/client-go/tools/clientcmd"
)

func main() {
    name := flag.String("name", "", "deployment name")
    ns := flag.String("n", "default", "namespace")
    flag.Parse()
    if *name == "" {
        fmt.Println("need -name")
        os.Exit(2)
    }

    cfg, err := clientcmd.BuildConfigFromFlags("", os.Getenv("HOME")+"/.kube/config")
    if err != nil {
        panic(err)
    }
    cli, err := kubernetes.NewForConfig(cfg)
    if err != nil {
        panic(err)
    }

    d, err := cli.AppsV1().Deployments(*ns).Get(context.Background(), *name, metav1.GetOptions{})
    if err != nil {
        panic(err)
    }

    desired := int32(1)
    if d.Spec.Replicas != nil {
        desired = *d.Spec.Replicas
    }
    ready := d.Status.ReadyReplicas
    updated := d.Status.UpdatedReplicas

    fmt.Printf("deployment=%s/%s desired=%d updated=%d ready=%d\n", *ns, *name, desired, updated, ready)
    if ready == desired && updated == desired {
        fmt.Println("rollout: healthy")
        os.Exit(0)
    }
    fmt.Println("rollout: pending")
    os.Exit(1)
}

Step-by-Step Explanation

Build Kubernetes client config from kubeconfig.
Scope operations by namespace or resource type.
Query or watch API objects.
Extract actionable status fields.
Return output and exit codes suitable for scripts and CI.

Code Anatomy

Setup phase creates client and context.
Query/watch phase pulls cluster state.
Presentation phase prints concise operational results.

Learning Goals

Use client-go safely and predictably.
Convert API objects into operator-facing insights.
Build automation-friendly cluster checks.