Demo Create A Deployment From Spec

The reconciler can now fetch the WebApp custom resource. Next, we need to build the desired Deployment object in Go. At this stage the helper only constructs the in-memory Deployment object — it does not yet call the Kubernetes API. This section focuses on the shape of the Deployment the controller will want to create.

The image is a slide with the title "Create A Deployment From Spec" on the left and the word "Demo" on the right. It also includes a copyright notice for KodeKloud.

Add imports

Open the controller file and add imports for the built-in Kubernetes types we’ll use. These provide the Deployment, Pod template types, and metadata helpers.

package controller

import (
    "context"

    "k8s.io/apimachinery/pkg/runtime"
    metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
    ctrl "sigs.k8s.io/controller-runtime"
    "sigs.k8s.io/controller-runtime/pkg/client"
    "sigs.k8s.io/controller-runtime/pkg/log"

    webappv1 "github.com/kodekloud/webapp-operator/api/v1"
    appsv1 "k8s.io/api/apps/v1"
    corev1 "k8s.io/api/core/v1"
)

Reconcile skeleton and helper signature

Keep the Reconcile skeleton that reads the WebApp resource. We’ll add a helper named deploymentFor that builds the Deployment object for a given *webappv1.WebApp.

func (r *WebAppReconciler) Reconcile(ctx context.Context, req ctrl.Request) (ctrl.Result, error) {
    log := log.FromContext(ctx)

    var webapp webappv1.WebApp
    if err := r.Get(ctx, req.NamespacedName, &webapp); err != nil {
        return ctrl.Result{}, client.IgnoreNotFound(err)
    }

    log.Info("fetched WebApp", "image", webapp.Spec.Image, "replicas", webapp.Spec.Replicas)
    return ctrl.Result{}, nil
}

func deploymentFor(w *webappv1.WebApp) *appsv1.Deployment

Build labels

Use a Go map to hold labels that will be applied to both the Deployment selector and the pod template. The selector and template labels must match so the Deployment can find and manage its Pods.

func deploymentFor(w *webappv1.WebApp) *appsv1.Deployment {
    labels := map[string]string{"app": w.Name}
    // ...
}

Ensure the Deployment selector and the Pod template labels are identical. If they differ, the Deployment will not manage the Pods you expect.

Replicas as a pointer

Kubernetes expects spec.replicas to be an optional pointer (*int32). Create a local variable, then pass its address into the Deployment spec.

func deploymentFor(w *webappv1.WebApp) *appsv1.Deployment {
    labels := map[string]string{"app": w.Name}
    replicas := w.Spec.Replicas
    // ...
}

replicas must be passed as a pointer (e.g., Replicas: &replicas) because the API type defines it as *int32. Using a plain numeric literal will cause compile-time errors.

Build the Deployment struct

Create the appsv1.Deployment struct literal with metadata, selector, and a Pod template. The Pod template contains a corev1.PodSpec with a single container named web. The container image comes from the WebApp spec and we expose port 80 inside the Pod.

func deploymentFor(w *webappv1.WebApp) *appsv1.Deployment {
    labels := map[string]string{"app": w.Name}
    replicas := w.Spec.Replicas

    return &appsv1.Deployment{
        ObjectMeta: metav1.ObjectMeta{
            Name:      w.Name,
            Namespace: w.Namespace,
            Labels:    labels,
        },
        Spec: appsv1.DeploymentSpec{
            Replicas: &replicas,
            Selector: &metav1.LabelSelector{MatchLabels: labels},
            Template: corev1.PodTemplateSpec{
                ObjectMeta: metav1.ObjectMeta{Labels: labels},
                Spec: corev1.PodSpec{
                    Containers: []corev1.Container{{
                        Name:  "web",
                        Image: w.Spec.Image,
                        Ports: []corev1.ContainerPort{{
                            ContainerPort: 80,
                        }},
                    }},
                },
            },
        },
    }
}

This helper establishes the first clear connection between your custom resource and a built-in Kubernetes workload: the WebApp tells the operator which image and replica count it wants, and the helper translates that into a Deployment object.

Types used

Type	Purpose	Example
`appsv1.Deployment`	Represents the Kubernetes Deployment object	`&appsv1.Deployment{ ... }`
`corev1.PodSpec`	Describes the Pod template spec inside the Deployment	`corev1.PodSpec{Containers: ...}`
`metav1.ObjectMeta`	Metadata for name, namespace, labels, etc.	`metav1.ObjectMeta{Name: w.Name}`

Build and verify

Run go build ./... in your module root. A clean build (no compiler errors) verifies imports, field names, and pointer usage. If the build fails, check for:

Missing imports (e.g., metav1, appsv1, corev1)
Incorrect field names or types
Passing a non-pointer where a pointer is required

At this stage the helper constructs the desired Deployment but does not yet contact the API server. The helper answers: “If this WebApp exists, what Deployment object should represent it?” In a subsequent step you will call deploymentFor from Reconcile and create or update the Deployment via the controller-runtime client.

Watch Video

Lab Solution Install The CRD And Run The Operator

Demo Wire The Deployment Into Reconcile

Introduction to Operator Fundamentals

Custom Resource Definitions Deep Dive

Kubebuilder Scaffolding

Building The WebApp Operator Core Reconcile

Running Testing Debugging Locally

Status Conditions Events

Finalizers And Cleanup

Validation Webhooks And CEL Policies

Packaging And Distribution

Alternative Approaches Operator SDK Helm Operator

Consuming Popular Operators

Production Readiness Testing Wrap Up

Demo Create A Deployment From Spec

Add imports

Reconcile skeleton and helper signature

Build labels

Replicas as a pointer

Build the Deployment struct

Types used

Build and verify

Watch Video

​Add imports

​Reconcile skeleton and helper signature

​Build labels

​Replicas as a pointer

​Build the Deployment struct

​Types used

​Build and verify

Watch Video

Add imports

Reconcile skeleton and helper signature

Build labels

Replicas as a pointer

Build the Deployment struct

Types used

Build and verify