kubernetes-introduction

Kubernetes Introduction

Kubernetes, also known as k8s, is an open-source container orchestration platform that automates the deployment, scaling, and management of containerized applications. It provides a way to abstract the underlying infrastructure and manage applications at scale, while also offering flexibility, portability, and a rich feature set. Kubernetes has become the de facto standard for container orchestration due to its widespread adoption, active community, and ability to handle complex, multi-tiered applications.

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Setting Up Kubernetes

To set up a Kubernetes cluster, you need to choose a deployment environment, install Kubernetes components on each node, configure networking using a plugin, initialize the master node with kubeadm init, join worker nodes using kubeadm join, deploy applications with manifests, and manage the cluster using kubectl or a management tool.

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Installing a Local Cluster

To install and configure a Kubernetes cluster on CentOS 7 or Ubuntu, you would need to setup the prerequisites and requirements for setting up a Kubernetes cluster after which you would be installing the Kubernetes components, including Kubeadm, Kubelet, and Kubectl and then you’ll need to connect the master and the worker nodes. Once the connection is established you can check it by deploying application on the cluster.

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Choosing a Managed Provider

A managed provider is a cloud-based service that provides a managed Kubernetes environment. This means that the provider handles the underlying infrastructure, such as servers, storage, and networking, as well as the installation, configuration, and maintenance of the Kubernetes cluster.

When choosing a managed Kubernetes provider, consider the cloud provider you are using, features and capabilities, pricing and billing, support, security and compliance, and the provider’s reputation and reviews. By taking these factors into account, you can select a provider that meets your needs and offers the best value for your organization.

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articleChoosing a Managed Kubernetes Provider

| Key Consideration                    | Description                                                                 |
|--------------------------------------|-----------------------------------------------------------------------------|
| __Ease of Use__                      | Providers offer varying degrees of automation and support; ease of deployment matters. |
| __Multi-Cloud and Hybrid Support__   | Some providers offer better multi-cloud or hybrid deployment options than others. |
| __Integration with Native Services__ | The ability to seamlessly integrate with native cloud services is crucial for complex workloads. |
| __Cost Considerations__              | Pricing models vary significantly, so cost transparency and predictability are key. |
| __Security Features__                | Built-in security measures and compliance support vary by provider.         |
| __Support and SLAs__                 | Availability of support and service-level agreements (SLAs) affect reliability and operational confidence. |
| __Scalability and Performance__      | Different providers offer varying capabilities for scaling workloads efficiently. |

Compare Kubernetes providers

Provider	Ease of Use	Multi-Cloud/Hybrid	Integration with Native Services	Cost	Security Features	Support and SLAs	Scalability and Performance
AWS EKS	Moderate	Strong hybrid (Outposts)	Excellent (AWS services)	Pay-as-you-go, complex	Advanced security options	Robust SLAs and support	High scalability
GKE	Easy (strong automation)	Multi-cloud support (Anthos)	Excellent (Google Cloud services)	Transparent pricing	Strong security built-in	Good support	High performance and scale
Azure AKS	Easy (integrated with Azure tools)	Hybrid support (Azure Stack)	Excellent (Azure services)	Competitive pricing	Comprehensive security	Good support	High scalability
IBM Cloud	Moderate	Hybrid support (Red Hat OpenShift)	Decent integrations	Competitive pricing	Enterprise-grade security	Strong enterprise support	Solid scalability

Deploying your First Application

To deploy your first application in Kubernetes, you need to create a deployment and service manifest in YAML files, apply the manifests to your Kubernetes cluster using the kubectl apply command, verify that your application’s pods are running with kubectl get pods, and test the service with kubectl get services and accessing the service using a web browser or a tool like cURL. There are also various tools and platforms available that can simplify application deployment in Kubernetes, such as Helm charts and Kubernetes operators.

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How Does `kubectl` Work?

kubectl communicates directly with the Kubernetes API server that manages the cluster’s control plane. When you issue a command, kubectl interacts with the Kubernetes API to retrieve information or make changes to the state of the cluster.

Why is `kubectl` Important?

Cluster Management: It simplifies managing Kubernetes resources such as Pods, services, and deployments by converting command-line inputs into API calls that are sent to the Kube API server.
Automation: kubectl allows for automation of tasks, such as scaling applications or managing configurations, which are crucial for maintaining cluster reliability and performance.
Troubleshooting: It provides the ability to introspect and troubleshoot running Kubernetes workloads by retrieving logs, monitoring events, and inspecting the status of various components.

How `kubectl` Works

kubectl communicates with the Kube API server over HTTPS. The process can be broken down as follows:

The user issues a kubectl command (e.g., kubectl get pod).
kubectl transforms the command into an API request and sends it to the Kube API server over HTTPS.
The Kube API server processes the request by querying etcd, the cluster’s database.
The Kube API server sends the response back to kubectl.
kubectl interprets the API response and displays it in a readable format for the user.

`kubectl` Configuration

To use kubectl, it must first be configured with the location and credentials of a Kubernetes cluster. Configuration details are stored in the user’s home directory, specifically in ~/.kube/config. This file contains information about:

Clusters: List of available Kubernetes clusters.
Contexts: Specific combinations of clusters, namespaces, and user credentials.
Credentials: User authentication information.

Viewing Configuration

To inspect the current kubectl configuration:

kubectl config view

This command displays the configuration of the kubectl tool itself, while other kubectl commands show configurations of the cluster or workloads.

Key `kubectl` Syntax

kubectl commands follow a consistent syntax pattern:

kubectl [command] [TYPE] [NAME] [flags]

Command: The action to be performed, such as get, describe, apply, delete, or logs.
TYPE: The type of Kubernetes object, such as pod, service, deployment, or node.
NAME: The name of the specific object (optional, especially for listing commands).
Flags: Optional arguments to modify the command output or behavior, such as -o=yaml for YAML output or --context to specify a different cluster context.

Example Commands

List all Pods:
```
kubectl get pods
```
Get information on a specific Pod:
```
kubectl get pod my-test-app
```
Show detailed information about a Pod:
```
kubectl describe pod my-test-app
```
View Pod details in YAML format:
```
kubectl get pod my-test-app -o=yaml
```
Get Pods with additional node information:
```
kubectl get pods -o=wide
```

Practical Uses of `kubectl`

Creating Kubernetes Objects: Apply configurations via manifest files (YAML/JSON) to create Pods, services, and other Kubernetes objects.
```
kubectl apply -f [manifest_file.yaml]
```
Viewing and Deleting Objects: Inspect the state of resources and delete them when necessary.
```
kubectl delete pod [POD_NAME]
```
Viewing Logs: Retrieve logs from running Pods for troubleshooting.
```
kubectl logs [POD_NAME]
```
Exporting Configurations: Use -o=yaml to export configuration details for recreating or troubleshooting in another cluster.

Introspection in Kubernetes with `kubectl`

Introspection is the process of gathering information about the state of your applications running within a Kubernetes cluster. Using kubectl, you can gather detailed insights about Pods, containers, and services to troubleshoot and debug issues effectively.

Key `kubectl` Commands for Introspection

Get Pods
- Command: kubectl get pods
- This command lists all the Pods in the current namespace, showing their status, which can be one of the following:
  - Pending: The Pod is accepted but not yet scheduled.
  - Running: The Pod is successfully attached to a node and is running its containers.
  - Succeeded: All containers in the Pod have terminated successfully and will not restart.
  - Failed: One or more containers in the Pod terminated with a failure and will not restart.
  - Unknown: The state of the Pod cannot be determined due to communication issues.
  - CrashLoopBackOff: The Pod’s container is crashing repeatedly.
Describe Pod
- Command: kubectl describe pod [POD_NAME]
- This command provides detailed information about a specific Pod, including:
  - Pod status
  - Node name
  - Labels
  - Container states (waiting, running, or terminated)
  - Resource requirements
  - IP addresses
  - Events related to the Pod (e.g., failed scheduling or image pull errors)
Execute Command in a Container
- Command: kubectl exec [POD_NAME] -- [COMMAND]
- Use this command to run a single command inside a container. This is useful for executing diagnostic commands like ping or curl.
- Interactive Shell: For an interactive shell session, use the -it switch:
```
kubectl exec -it [POD_NAME] -- /bin/bash
```
- Here, -i enables interactive mode and -t allocates a TTY.
View Logs
- Command: kubectl logs [POD_NAME]
- This command retrieves the logs from the specified Pod, providing insights into what is happening inside the application.
- If the Pod contains multiple containers, specify which container to get logs from using the -c flag:
```
kubectl logs [POD_NAME] -c [CONTAINER_NAME]
```

Best Practices for Debugging

Avoid Directly Installing Software in Containers: While you can use kubectl exec to install tools for debugging, it’s not recommended. Changes made this way are ephemeral and will be lost when the container restarts.
Build Custom Container Images: Instead of making temporary fixes, create new container images that include the necessary tools or configurations, and then redeploy them.
Integrate Findings: Use the insights gained from introspection to make informed changes to your container images and application configurations.

kubernetes-introduction

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