## Namespace Definition

```yaml
apiVersion: v1
kind: Namespace
metadata:
  name: my-ns
```

- **apiVersion**: Specifies the version of the Kubernetes API.
- **kind**: Defines the type of Kubernetes object, here it's a `Namespace`.
- **metadata**: Contains data that helps uniquely identify the object, including a `name`.

This YAML file creates a namespace named `my-ns` which isolates a group of resources within Kubernetes.

## Pod Definitions

### Nginx Pod

```yaml
apiVersion: v1
kind: Pod
metadata:
  namespace: my-ns
  name: nginx-pod
  labels:
    app: app1
    zone: staging
    version: v1.0.1
    app.kubernetes.io/product: nginx-pod
spec:
  containers:
    - name: naginx-container
      image: nginx:latest
      ports:
        - containerPort: 80
```

- **metadata.namespace**: Specifies the namespace the pod belongs to (`my-ns`).
- **metadata.name**: The name of the pod (`nginx-pod`).
- **metadata.labels**: Key-value pairs for organizing and selecting resources.
- **spec.containers**: Specifies the containers within the pod. Each container has:
  - **name**: Container name.
  - **image**: The Docker image to run (`nginx:latest`).
  - **ports**: List of ports to expose from the container (`containerPort: 80`).

This file defines a pod named `nginx-pod` running the latest Nginx container in the `my-ns` namespace.

### Test Pod 1

```yaml
apiVersion: v1
kind: Pod
metadata:
  namespace: my-ns
  name: testpod1
spec:
  containers:
    - name: c00
      image: ubuntu
      command: ["/bin/bash", "-c", "while true; do echo Hello-Coder; sleep 5 ; done"]
    - name: c01
      image: ubuntu
      command: ["/bin/bash", "-c", "while true; do echo Hello-Programmer; sleep 5 ; done"]
```

- **spec.containers.command**: Overrides the default command for the container, in this case, running a looped bash script that prints a message every 5 seconds.

This defines a pod named `testpod1` with two Ubuntu containers in the `my-ns` namespace, each running a different command.

## Pod with Resource Requests and Limits

```yaml
apiVersion: v1
kind: Pod
metadata:
  namespace: my-ns
  name: testpod1
spec:
  containers:
    - name: c00
      image: ubuntu
      command:
        - /bin/bash
        - -c
        - while true; do echo Hello-Coder; sleep 5 ; done
    - name: c01
      image: ubuntu
      command:
        - /bin/bash
        - -c
        - while true; do echo Hello-Programmer; sleep 5 ; done
      resources:
        limits:
          memory: "128Mi"
          cpu: "500m"
        requests:
          memory: "64Mi"
          cpu: "250m"
```

- **resources.limits**: Specifies the maximum amount of resources a container can use.
- **resources.requests**: Specifies the amount of resources a container is guaranteed.

This pod configuration defines resource limits and requests for the containers to ensure they do not exceed specific memory and CPU usage.

## Pod with NodeSelector

```yaml
apiVersion: v1
kind: Pod
metadata:
  namespace: my-ns
  name: testpod3
spec:
  containers:
    - name: c00
      image: ubuntu
      command:
        - /bin/bash
        - -c
        - while true; do echo Hello-Coder; sleep 5 ; done
    - name: c01
      image: ubuntu
      command:
        - /bin/bash
        - -c
        - while true; do echo Hello-Programmer; sleep 5 ; done
      resources:
        limits:
          memory: "128Mi"
          cpu: "500m"
        requests:
          memory: "64Mi"
          cpu: "250m"
  nodeSelector:
    kubernetes.io/hostname: k8s2
    kubernetes.io/disk: ssd
```

- **nodeSelector**: Ensures the pod is scheduled on nodes with the specified labels (`kubernetes.io/hostname: k8s2` and `kubernetes.io/disk: ssd`).

This configuration places the pod on specific nodes that match the given labels.

## Simple Pod Templates

### Basic Pod

```yaml
apiVersion: v1
kind: Pod
metadata:
  name: myapp
  labels:
    name: myapp
spec:
  containers:
  - name: myapp
    image: <Image>
    resources:
      limits:
        memory: "128Mi"
        cpu: "500m"
    ports:
      - containerPort: <Port>
```

This is a template for a basic pod named `myapp` with configurable image and port settings.

### Nginx Pod

```yaml
apiVersion: v1
kind: Pod
metadata:
  name: my-pod
  labels:
    app: MyApp
spec:
  containers:
  - name: my-container
    image: nginx:latest
    ports:
    - containerPort: 80
```

This defines a pod named `my-pod` running an Nginx container exposing port 80.