AKS 19 – Explain Deployment Manifest file

apiVersion: apps/v1

• What it does: Specifies the API version of the Kubernetes object you’re using.
• Why it’s used: apps/v1 is the stable version for managing Deployments in Kubernetes. It ensures compatibility with the Kubernetes API server.

kind: Deployment

• What it does: Declares the type of Kubernetes object.
• Why it’s used: A Deployment manages a ReplicaSet and ensures the desired number of pod replicas are running and updated.

metadata:

• What it does: Provides metadata about the object.
• Why it’s used: Helps identify and organize the object.

name: welcome-app

Name of the Deployment. Used to reference this object.

labels:

    app: welcome-app

Labels are key-value pairs used for grouping and selecting resources.

spec:

• What it does: Defines the desired state of the Deployment.

replicas: 3

Why it’s used: Specifies that 3 pods of the application should be running at all times.

Why it’s used: Tells the Deployment which pods to manage, based on matching labels.

template:

• What it does: Describes the pod template used to create pods.

Why it’s used: Labels applied to pods created by this Deployment. Must match the selector above.

spec: (inside template)

• What it does: Defines the pod specification.

Why it’s used: Defines a container named welcome-app inside the pod.

Why it’s used: Specifies the container image to use. This one is pulled from an Azure Container Registry.

Why it’s used: Exposes port 80 inside the container, typically for HTTP traffic.

envFrom: (under container)

• What it does: Loads environment variables into the container.

Why it’s used: Loads all key-value pairs from the welcome-config ConfigMap as environment variables.

• Why it’s used: Loads sensitive data (like passwords, API keys) from the welcome-secrets Secret as environment variables.

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✅ Summary

This Deployment ensures:

• 3 replicas of the welcome-app pod are always running.
• Each pod runs a container from a specified image.
• Environment variables are injected from a ConfigMap and a Secret.
• Port 80 is exposed for incoming traffic.