Creating Deployments with YAML in Kubernetes - Visual Walkthrough

Process Flow - Creating Deployments with YAML

Write YAML file

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kubectl apply -f file.yaml

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Kubernetes API Server receives

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Deployment object created

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ReplicaSet created

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Pods created and running

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Deployment ready

The flow starts with writing a YAML file, then applying it with kubectl, which creates a Deployment object. Kubernetes then creates ReplicaSets and Pods until the Deployment is ready.

Execution Sample

Kubernetes

apiVersion: apps/v1
kind: Deployment
metadata:
  name: myapp-deployment
spec:
  replicas: 2
  selector:
    matchLabels:
      app: myapp
  template:
    metadata:
      labels:
        app: myapp
    spec:
      containers:
      - name: myapp-container
        image: nginx:1.21

This YAML defines a Deployment named 'myapp-deployment' with 2 replicas running nginx version 1.21.

Process Table

Step	Action	Resource Created	State Change	Output/Status
1	kubectl apply -f deployment.yaml	Deployment 'myapp-deployment'	Deployment object created in cluster	deployment.apps/myapp-deployment created
2	Kubernetes creates ReplicaSet	ReplicaSet for 'myapp-deployment'	ReplicaSet object created	replicaset.apps/myapp-deployment-xxxxx created
3	ReplicaSet creates Pods	2 Pods with label app=myapp	Pods created and starting	pod/myapp-deployment-xxxxx-1 created pod/myapp-deployment-xxxxx-2 created
4	Pods start running	Pods status changes	Pods become Ready	pod/myapp-deployment-xxxxx-1 Ready pod/myapp-deployment-xxxxx-2 Ready
5	Deployment status updated	Deployment reports ready replicas	Deployment ready with 2 replicas	deployment.apps/myapp-deployment available

💡 Deployment is ready when all replicas are running and available.

Status Tracker

Resource	Initial	After Step 1	After Step 2	After Step 3	After Step 4	Final
Deployment	None	Created	Created	Created	Created	Ready with 2 replicas
ReplicaSet	None	None	Created	Created	Created	Active with 2 pods
Pods	None	None	None	Created (2 pods)	Running (2 pods)	Ready (2 pods)

Key Moments - 3 Insights

Why does the Deployment create a ReplicaSet before Pods?

The Deployment manages ReplicaSets to control Pods. As shown in execution_table step 2, the ReplicaSet is created first to manage the desired number of Pods.

What does 'kubectl apply' do with the YAML file?

It sends the YAML to Kubernetes API Server to create or update resources. Execution_table step 1 shows the Deployment object creation after applying the YAML.

When is the Deployment considered ready?

When all Pods are running and available. Execution_table step 5 shows the Deployment status updated to ready with 2 replicas.

Visual Quiz - 3 Questions

Look at the execution_table, what resource is created immediately after applying the YAML file?

A Deployment

B Pods

C ReplicaSet

D Service

💡 Hint

Check execution_table step 1 for the resource created by 'kubectl apply'.

At which step do the Pods become Ready according to the execution_table?

A Step 2

B Step 4

C Step 3

D Step 5

💡 Hint

Look at the 'Pods start running' action in execution_table step 4.

If the replicas count in YAML is changed from 2 to 3, what changes in the variable_tracker for Pods?

A Pods remain at 2 throughout

B Pods increase to 3 after Step 1

C Pods increase to 3 after Step 3

D Pods increase to 3 after Step 5

💡 Hint

Pods are created by ReplicaSet after Step 2, see variable_tracker Pods row.

Concept Snapshot

Creating a Deployment with YAML:
- Write a YAML file with apiVersion, kind: Deployment, metadata, and spec.
- Use 'kubectl apply -f file.yaml' to create the Deployment.
- Kubernetes creates a ReplicaSet to manage Pods.
- Pods are created and run the specified container image.
- Deployment is ready when all replicas are running.

Full Transcript

To create a Deployment in Kubernetes, you write a YAML file describing the Deployment resource, including the number of replicas and container details. Then you run 'kubectl apply -f' with that YAML file. Kubernetes creates the Deployment object, which in turn creates a ReplicaSet. The ReplicaSet manages the Pods, creating the specified number of Pods running the container image. When all Pods are running and ready, the Deployment status updates to ready. This process ensures your application runs with the desired number of instances.