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Containerization & Orchestration/Kubernetes/1-Information.md Executable file
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# Kubernetes (K8s) Documentation
## Overview
**Kubernetes (K8s)** is an open-source container orchestration platform designed to automate the deployment, scaling, and operation of containerized applications.
---
## Control Plane (CP)
The **Control Plane** is the core management component of a Kubernetes cluster. It makes global decisions about the cluster (e.g., scheduling), and it maintains the desired state of the cluster by managing workloads and directing communication within the system.
> **Note:** By default, the Control Plane does not directly manage or run application containers.
### Key Components of the Control Plane:
- **API Server (`kube-apiserver`)**:
Exposes the Kubernetes API and serves as the entry point to the cluster. It handles communication between internal components and external clients.
- **Scheduler (`kube-scheduler`)**:
Assigns work (e.g., pods) to nodes based on resource availability and policies.
- **Controller Manager (`kube-controller-manager`)**:
Runs controllers that regulate the state of the cluster (e.g., Node Controller, Replication Controller, etc.).
- **etcd**:
A consistent, highly-available key-value store that stores all cluster data, configurations, and states. This is the "database" of Kubernetes.
---
## Worker Nodes
Worker nodes are the machines where containerized applications run. Each worker node contains essential components for managing containers.
### Key Components of a Worker Node:
- **Kubelet**:
An agent that ensures containers are running as specified in their Pod definitions. It communicates with the Control Plane to receive and execute tasks.
- **Kube Proxy**:
Maintains network rules and handles routing for communication between services within the cluster and with external traffic.
---
## Data Flow
- **Kubelet** and **Kube Proxy** on each worker node communicate with the **API Server** in the Control Plane for task execution and resource updates.
- The **Scheduler** assigns pods to nodes based on resource requirements, while the **Controller Manager** ensures that the cluster state remains consistent.
---
## Administration Tools
- **`kubeadm`**:
A tool for bootstrapping Kubernetes clusters. It simplifies the setup and configuration of the Control Plane and worker nodes.
- **`kubectl`**:
The command-line interface (CLI) for interacting with the Kubernetes API. It is used to manage resources, deploy applications, and inspect cluster components.
---
## Kubernetes Version Compatibility
### Kubernetes and Container Runtimes:
- **Kubernetes ≤ 1.23**:
Compatible with Docker as the default container runtime.
- **Kubernetes 1.24 to 1.25**:
Docker is not supported as a runtime. These versions require `containerd` or another Container Runtime Interface (CRI) implementation.
- **Kubernetes ≥ 1.25**:
Docker can be installed on the server but must be used indirectly through `containerd` or another CRI-compliant runtime. Docker itself is not a supported runtime.

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Containerization & Orchestration/Kubernetes/2-Installtion.md Executable file
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---
# Containerd and Kubernetes Installation Guide
## 1. Disable Swap
Turn off swap and disable it permanently.
```bash
swapoff -a
sed -i '/swap/d' /etc/fstab
```
## 2. Enable Required Kernel Modules
Create a configuration file to load necessary kernel modules and load them temporarily.
```bash
echo -e "overlay\nbr_netfilter" | sudo tee /etc/modules-load.d/containerd.conf
sudo modprobe overlay
sudo modprobe br_netfilter
```
## 3. Enable IPv4 Forwarding
Enable IPv4 forwarding in the sysctl configuration and apply the changes.
```bash
sed -i 's/#net.ipv4.ip_forward=1/net.ipv4.ip_forward=1/' /etc/sysctl.conf
sysctl -p
```
## 4. Configure Containerd
Generate the default configuration for Containerd and modify it to use systemd as the cgroup driver.
```bash
containerd config default | sudo tee /etc/containerd/config.toml
sudo sed -i 's/SystemdCgroup = false/SystemdCgroup = true/' /etc/containerd/config.toml
```
## 5. Install Kubernetes
Add the Kubernetes package repository and install the required packages.
```bash
sudo mkdir -p /etc/apt/keyrings
curl -fsSL https://pkgs.k8s.io/core:/stable:/v1.30/deb/Release.key | sudo gpg --dearmor -o /etc/apt/keyrings/kubernetes-apt-keyring.gpg
echo 'deb [signed-by=/etc/apt/keyrings/kubernetes-apt-keyring.gpg] https://pkgs.k8s.io/core:/stable:/v1.30/deb/ /' | sudo tee /etc/apt/sources.list.d/kubernetes.list
sudo apt-get update
sudo apt-get install -y kubelet kubeadm kubectl
sudo apt-mark hold kubelet kubeadm kubectl
```
## 6. Enable kubelet
Enable and start the kubelet service.
```bash
sudo systemctl enable --now kubelet
```
## 7. Initialize the Kubernetes Cluster
Initialize the Kubernetes control plane with the specified parameters.
```bash
sudo kubeadm init --control-plane-endpoint 192.168.2.100 --apiserver-advertise-address 192.168.2.100 --pod-network-cidr 10.244.0.0/16 | tee kuber-install.log
```
## 8. Create Control Plane Join Command
Create the control plane join command and save it for later use.
```bash
sudo kubeadm init phase upload-certs --upload-certs
Copy the output certificate key and run the following command, replacing <CERTIFICATE_KEY> with the copied key.
sudo kubeadm token create --certificate-key <CERTIFICATE_KEY> --print-join-command | tee cp-command.txt
```
## 9. Join Control Plane and Worker Nodes
Use the command from cp-command.txt on your control plane nodes to join them. Additionally, get the join command for worker nodes from kuber-install.log and run it on each worker node.
---
This revised guide provides clear, step-by-step instructions, making it easier to follow and ensuring all necessary actions are covered.

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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
```