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# Kubernetes
## `kubectl` Command Reference
### Get State of API Resources
```bash
kubectl api-resources
```
### Node Management
- **Show all nodes:**
```bash
kubectl get node
```
### Namespace Management
- **List all namespaces:**
```bash
kubectl get namespaces
```
```bash
kubectl get ns
```
- **Create a custom namespace:**
```bash
kubectl create ns <namespace-name>
```
### Pod Management
- **Get the list of pods in the default namespace:**
```bash
kubectl get pod
```
- **Get the list of pods in the default namespace with full information:**
```bash
kubectl get pod -o wide
```
- **Get the list of pods in a custom namespace with full information:**
```bash
kubectl get pod -o wide -n <name-space>
```
### Running a Pod
- **Run a new pod:**
```bash
kubectl run <pod-name> <switch> {
--image=<image-name>, # Specifies the container image to use
--port=<portnumber>, # Specifies the port that the container exposes
-n <namespace-name>, # Specifies the namespace
--env="KEY=VALUE", # Sets environment variables in the container
--command, # Treats the rest of the arguments as the command to run in the container
--replicas=<number>, # Specifies the number of replicas for the deployment
--labels="key=value,key2=value2", # Adds labels to the pod(s)
--dry-run=client, # Prints the object that would be sent, without creating it
--restart=<Always|OnFailure|Never>, # Determines the restart policy for the pod
--overrides='<json>', # Provides a JSON override for the generated object
--image-pull-policy=<policy>, # Specifies the image pull policy (Always, IfNotPresent, Never)
--limits=cpu=<cpu>,memory=<memory>, # Specifies resource limits for the container
--requests=cpu=<cpu>,memory=<memory> # Specifies resource requests for the container
}
```
- *Example:*
```bash
kubectl run mypod --image=nginx --port=80 -n mynamespace \
--env="ENV_VAR_NAME=VALUE" --command -- nginx -g "daemon off;" \
--replicas=3 --labels="app=myapp,env=prod" --dry-run=client \
--restart=Always --overrides='{"spec": {"containers": [{"name": "nginx", "image": "nginx"}]}}' \
--image-pull-policy=IfNotPresent --limits=cpu=100m,memory=256Mi \
--requests=cpu=50m,memory=128Mi
```
### Deleting a Pod
- **Delete a pod in a custom namespace:**
```bash
kubectl delete pod -n <namespace-name> <pod-name>
```
### API Resource Documentation
- **Get documentation of an API resource:**
```bash
kubectl explain <api-resource-name>
```
- *Example:*
```bash
kubectl explain pod
```
### Logging and Pod Information
- **Get and follow logs of a pod (pod must be created and running):**
```bash
kubectl logs -f -n <namespace-name> <podname>
```
- **Get logs and state information of a pod (works at any time):**
```bash
kubectl describe pod -n <namespace-name> <podname>
```
### Apply Yaml File
```bash
kubectl apply -f <yaml-file> -n <namespace-name>
```

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# Kubernetes YAML Files
This document provides explanations and details for various Kubernetes YAML configurations, describing how different Kubernetes objects such as Namespaces, Pods, and other specifications are defined and utilized. The examples cover creating namespaces, deploying pods, setting resource limits, and using node selectors.
## 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.
## Useful Kubernetes Commands
### View Pod Details
```bash
kubectl get pod -n my-ns <pod-name> -o yaml
```
This command retrieves and displays the YAML configuration of the pod `testpod1` in the namespace `my-ns`.
### Label a Node
```bash
kubectl label node <node-name> kubernetes.io/<var-name>=<var-value>
kubectl get nodes --show-labels
```