Kubernetes – Concept of Containers

Prerequisite: Kubernetes

Kubernetes is an open-source container orchestration framework that was originally developed by Google.

So now, the question arises, “what’s container orchestration?”.

Container orchestration is automation. It can facilitate you to deploy the identical application across different environments like physical machines, virtual machines or cloud environments, or perhaps hybrid deployment environments and makes it easier for the management, scaling, and networking of containers.

The original name for Kubernetes (originates from Greek) within Google was Project 7. Within the year 2014 Kubernetes was released for the primary time and made open-sourced too after using it to run production workloads at scale for quite a decade. Also, pure open-source Kubernetes is free and might be downloaded from its repository on GitHub.

It is pronounced as “koo-burr-NET-eez”. It’s also referred to as k8s (k – eight characters – s), derived by replacing the eight letters with the digit 8.

Features of Kubernetes

Following are the various features or characteristics of Kubernetes:

1. Multi-Host Container Scheduling: Done by Kube-scheduler, it assigns containers, also referred to as pods in Kubernetes to nodes at runtime. It accounts for resources, quality of service, and policies before scheduling.
2. Scalability and availability: The Kubernetes master is often deployed during a highly available configuration. Multi-region deployments are available as well.
3. Flexibility and modularization: Kubernetes includes a plug-and-play architecture that permits you to increase it when you need to. There are specific add-ons from network drivers, service discovery, container runtime, visualization, and command. If there are tasks that you need to perform for your environment specifically, you’ll be able to create an add-on to suit your needs.
4. Registration: New worker nodes can register themselves with the Kubernetes master node.
5. Service discovery: Service discovery allows for automatic detection of new services and endpoints via DNS or environment variables.
6. Persistent storage: It is a much-requested feature when working with containers. Pods can use persistent volumes to store data and therefore the data is retained across pod restarts and crashes.
7. Maintenance: When it involves Kubernetes maintenance and upgrades, Kubernetes features are always backward compatible for some versions. All APIs are versioned and when upgrading or running maintenance on the host, you’ll unschedule the host so that no deployments can happen thereon. Once you’re done, you’ll simply turn the host back on and schedule deployments or jobs.
8. Logging and Monitoring: In terms of logging and monitoring, application monitoring or health checks are also built-in, TCP, HTTP, or container exact health checks are available out of the box. There are also health checks to give you the status of the nodes and failures monitored by the node controller. Kubernetes status can also be monitored via add-ons like Metrics Server, cAdvisor, and Prometheus. And lastly, you can use the built-in logging frameworks or if you choose, you can bring your own.
9. Secrets Management: Sensitive data is a first-class citizen in Kubernetes. Secrets mounted to data volumes or environment variables. They’re also specific to a single namespace so aren’t shared across all applications.

Architecture of Kubernetes

The architecture of Kubernetes includes a master node and one or more worker nodes.

Understanding the Master node:

• Kube-apiserver: a frontend of the cluster that allows you to interact with the Kubernetes API and connects to the etcd database.
• Kube-scheduler: schedules pods on specific nodes supported labels, taints, and tolerations set for pods
• etcd: a database, stores all cluster data which includes job scheduling info, pod details, stage information, etc.
• Kube – controller – manager: manages the current state of the cluster
• cloud – controller – manager: interacts with outside cloud manager

Different optional add-ons: DNS, Dashboard, cluster-level resource monitoring, cluster-level logging

Understanding the Worker node:

We wouldn’t get anywhere without Worker Nodes, though. These Worker Nodes are the Nodes where your applications operate. The Worker Nodes communicate back with the Master Node. Communication to a Worker Node is handled by the Kubelet Process.

• kubelet: passes requests to the container engine to ensure that pods are available
• Kube-proxy: runs on every node and uses iptables to provide an interface to connect to Kubernetes components
• container – runtime: take care of actually running container
• network agent: implements a software-defined networking solution

Containers of an application are tightly coupled together in a Pod. By definition, a Pod is the smallest unit that can be scheduled as deployment in Kubernetes.  Once Pods have been deployed, and are running, the Kubelet process communicates with the Pods to check on state and health, and therefore the Kube-proxy routes any packets to the Pods from other resources that might be wanting to communicate with them.

Installing of Kubernetes:

In this section, we will learn how to install Kubernetes on the Linux platform. So, follow the given steps for installing the Kubernetes:

Step 1: First of all, we have to update our apt-get repository.

sudo apt-get update

Step 2: Install apt transport HTTPS. This is basically used to make repositories while HTTPS.

sudo apt-get install -y apt-transport-https

Step 3: Install the docker dependency

sudo apt install docker.io

Step 4: After installing the docker we have to start and enable the docker.

sudo systemctl start docker
sudo systemctl enable docker

Step 5: We have to install the necessary components for Kubernetes. Before that, we have to install the curl command because the curl command is used to send the data using  URL syntax. Let’s install the curl command by:

sudo apt-get install curl

Step 6: Download an add key for Kubernetes installation from a URL.

sudo curl -s https://packages.cloud.google.com/apt/doc/apt-key.gpg | sudo apt-key add

Step 7: We have to add a repository in a certain location.

echo “deb https://apt.kubernetes.io/ kubernetes-xenial main” | sudo tee -a /etc/apt/sources.list.d/kubernetes.list

Step 8: Now check for any updates available.

sudo apt-get update

Step 9: Now we are going to install Kubernetes components.

sudo apt-get install -y kubectl kubeadm kubelet kubernetes-cni docker.io

Step 10: We have to initialize the master node and to do this we have to first use a swapoff command to disable the swapping on other devices.

sudo swapoff -a

Step 11: Go ahead with the initialization.

sudo kubeadm init

Step 12: To start using your cluster, you need to run the following as a regular user:

mkdir -p $HOME/.kube
sudo cp -i /etc/kubernetes/admin.conf $HOME/.kube/config
sudo chown $(id -u):$(id -g) $HOME/.kube/config

Step 13: To deploy paths, use the following command:

sudo kubectl apply -f https://raw.githubusercontent.com/coreos/flannel/master/Documentation/k8s-manifests/kube-flannel-rbac.yml

Step 14: To see all the pods you have, use the command:

sudo kubectl get pods --all-namespaces

Pros:

1. Scalability: Kubernetes allows for easy scaling of applications by increasing or decreasing the number of replicas of a particular service.
2. High availability: Kubernetes provides features such as self-healing and automatic failover, which help ensure that applications remain available even in the event of a node failure.
3. Portability: Kubernetes is designed to be platform-agnostic, which means that applications can be deployed on any infrastructure, whether it be on-premises, in the cloud, or at the edge.
4. Automation: Kubernetes automates many of the tasks associated with deploying and managing applications, such as rolling updates, service discovery, and load balancing.
5. Flexibility: Kubernetes allows for the use of multiple orchestration patterns, such as blue-green deployment, canary releases, and A/B testing, which gives developers more flexibility in how they deploy their applications.

Cons:

1. Complexity: Kubernetes can be complex to set up and manage, especially for organizations that are new to container orchestration.
2. Steep learning curve: There is a steep learning curve for understanding how to use Kubernetes effectively, and for troubleshooting issues that may arise.
3. Limited native support for certain technologies: Kubernetes does not natively support certain technologies, such as Windows containers, which can create challenges for organizations that use these technologies.
4. Networking complexity: Kubernetes networking can be complex, especially when working with multiple clusters or when trying to integrate with existing network infrastructure.
5. Higher resource requirements: running a Kubernetes cluster can consume more resources than running a traditional application, which can make it more expensive to operate.