What is Kubernetes?
- Definition of Kubernetes
- Kubernetes Architecture
- Critical Components of Kubernetes Cluster
- How does Kubernetes Work?
- Features of Kubernetes
- Benefits of Kubernetes
1. Definition of Kubernetes
Kubernetes is a container orchestration tool—an open-source, extensible platform for deploying, scaling, and managing the complete life cycle of containerized applications across a cluster of machines. Originally designed by Google, it is now maintained by Cloud Native Computing Foundation (CNCF). Kubernetes is Greek for the helmsman, and true to its name, it allows you to coordinate a fleet of containerized applications anywhere you want to run them: on-premises, in the cloud, or both.
Kubernetes has gained popularity because it overcomes many issues associated with using containers in production. It makes it simple to launch unlimited container replicas, distribute them across numerous physical hosts, and configure networking so that users can access your service.
Most developers begin their container experience using Docker. While this is a comprehensive tool, it is quite low-level, relying on command line interface (CLI) commands that interact with just one container at a time. Kubernetes provides considerably higher-level abstractions for creating applications and their infrastructure by utilizing declarative schemas that can be collaboratively developed.
2. Kubernetes Architecture
Kubernetes helps schedule and manage containers across groups of physical or virtual servers. The Kubernetes architecture separates a cluster into components that collaborate to maintain the cluster’s defined state.
A group of node machines used to run containerized apps is known as a Kubernetes cluster. A Kubernetes cluster is divided into two parts: the control plane and the compute machines or nodes. Each node, which can be a physical or virtual system, has its own Linux environment. Pods, which are composed of containers, are executed by each node.
Users communicate with their Kubernetes cluster using the Kubernetes API (application programming interface), which is the front end of the Kubernetes control plane. The Kubernetes API is essentially the interface used to create, manage, and configure Kubernetes clusters. It is the method of communication used by your cluster’s users, external components, and individual cluster members. The API server checks to see if a request is legitimate before processing it.
3. Critical Components of Kubernetes Cluster
Control Plane: A Kubernetes cluster is a collection of machines that collectively run containerized applications. A limited number of these are running programs that manage the cluster. They are known as master nodes, also collectively known as the control plane. The 5 main components of control plane nodes include:
- kube-apiserver: The scalable API server that serves as the front end of the Kubernetes control plane. It manages the cluster’s shared state of components using REST operations via external communication. The ‘kubectl’ client, which you install on a local computer, is the default mechanism for interacting with the cluster.
- etcd: A distributed key-value store. This is the Kubernetes foundation, which is used for storing and duplicating important data for distributed systems. All metadata, configuration, and state data in this database are managed by the control-plane node.
- kube-controller-manager: A control plane component made up of node, replication, endpoint, and service account and token controllers. To reduce complexity, the control-plane node runs these individual controllers as a single process.
- kube-scheduler: A control plane component that determines on which node a newly created pod will run.
- cloud-controller-manager: A component that interacts with different cloud providers. When requested, this manager updates cluster state information, adjusts needed cloud resources, and creates and maps additional cloud services.
Nodes: End-user container workloads and services are run on a node server in a Kubernetes cluster. Node servers are made up of three parts:
- A container runtime: the core component that allows containers to function. The most well-known is Docker, although Kubernetes also supports containerd, CRI-O, and anything designed with the Kubernetes container runtime interface.
- kubelet: An agent that runs on each node and guarantees that all Kubernetes containers are functioning properly.
- kube-proxy: A network proxy that runs on each node to keep network rules consistent across the cluster. Kube-proxy ensures that communication reaches your pods.
Pods: A pod is the most basic compute unit that a Kubernetes cluster can generate and deploy. A pod can include a single container or a group of containers that work closely together, share a lifecycle, and communicate. Each pod is managed by Kubernetes as a single object with a shared environment, storage volumes, and IP address space. In this deployment architecture, Kubernetes maintains the pods rather than the containers directly. Kubernetes assigns each pod its own IP address space. The network namespace, which includes the IP address and network ports, is shared by all containers in a pod.
Service: A service is a simple way to define and expose an application that runs on a set of pods. The goal behind a service is to combine a collection of pods into a single resource. Many services can be developed within a single microservices-based application. Services provide critical cluster capabilities such as load balancing, service discovery, and support for zero-downtime application deployments.
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4. How does Kubernetes Work?
Kubernetes is an open-source container orchestration platform that automates the deployment, scaling, and management of containerized applications. It allows you to manage a cluster of containers as a single system, providing a highly flexible and scalable infrastructure for running applications.
At its core, Kubernetes uses a master-worker architecture. The master node acts as the control plane and manages the cluster, while the worker nodes host and run the containers.
Here’s a high-level overview of how Kubernetes works:
- Containers: Kubernetes works with containers, which are lightweight and isolated environments that package an application along with its dependencies.
- Cluster: You start by setting up a Kubernetes cluster, which consists of multiple worker nodes. Each worker node runs a container runtime (e.g., Docker) and communicates with the master node.
- Pods: The smallest unit in Kubernetes is a Pod, which is a logical group of one or more containers that share network and storage resources. Pods are scheduled onto worker nodes by the master node.
- Master Node: The master node is responsible for managing and coordinating the cluster. It maintains the desired state of the cluster by continuously monitoring and making adjustments as needed.
- API Server: The API server is the central control point for the cluster. It exposes the Kubernetes API, which allows users and other components to interact with the cluster.
- Scheduler: The scheduler is responsible for assigning Pods to worker nodes based on resource requirements, policies, and constraints. It strives to balance the workload across the cluster.
- Controller Manager: The controller manager is a collection of controllers that handle different aspects of the cluster. It ensures that the current state of the cluster matches the desired state defined in the Kubernetes objects.
- etcd: The etcd is a distributed key-value store that Kubernetes uses to store and manage cluster configuration data, state information, and metadata.
- Worker Nodes: Worker nodes are the machines where your containers are actually run. Each worker node runs a container runtime (such as Docker) and a kubelet, which communicates with the master node and manages the containers running on that node.
- Services: Kubernetes provides a way to expose containers running in a Pod to the network through Services. Services abstract the underlying Pods and provide a stable IP address and DNS name to access the containers.
- Scaling and Self-healing: Kubernetes allows you to scale your applications horizontally by adding or removing Pods based on demand. It also provides automatic recovery and fault tolerance by restarting failed containers or rescheduling them onto healthy nodes.
Kubernetes offers a wide range of features and functionalities to manage containerized applications effectively. It abstracts away the complexity of managing individual containers and provides a unified platform for deploying and scaling applications with ease.
Traffic Flow in Kubernetes:
- East-West Traffic: refers to the communication between different pods (containers) within the same cluster. When one pod needs to talk to another pod, it’s considered east-west traffic. It’s called east-west because the communication happens horizontally, like moving from one room to another within a building, rather than going in and out of the cluster (north-south traffic), like entering or exiting the main building. This is not secured in Kubernetes by default.
- North-South Traffic: refers to the communication between the external world and the pods within the cluster. When a user or an external service interacts with the cluster, it’s considered north-south traffic. It’s called north-south because the communication flows vertically, like going in and out of a building, representing the traffic that enters or exits the cluster. This is secured by API Gateway/API Management/Ingress Gateway.
Role of Service Mesh:
A service mesh is an infrastructural layer that is specifically designed to handle secure traffic management and service-to-service communication. Kubernetes uses it most frequently for security, authentication, and permission. Its components consist of a Control plane, which serves as the brain and configures the proxies, and a Data plane, which is made up of lightweight proxies like sidecars and is the hub of activity.
Kubernetes uses SSL/TLS certificates to authenticate and encrypt communication when engaging with clusters and within clusters. The parties at either end of a network connection are validated (often by using a private key) when using a service mesh with a Mutual TLS (mTLS), and internal pod communication is secure, quick, and reliable.
In Kubernetes, a service mesh is beneficial because it enhances the capabilities of the platform for managing microservices. It provides advanced features like traffic routing, load balancing, encryption, and monitoring at the service level. Service mesh vendors like Istio or Linkerd integrate seamlessly with Kubernetes and help simplify complex networking tasks within the cluster. They offer additional control and observability, allowing for better management of microservices, improving reliability, and security, and enabling easier troubleshooting and debugging in a distributed environment.
Role of Ingress:
In Kubernetes, Ingress plays a role in securing traffic by acting as a gateway for incoming requests from external sources. It acts as a traffic controller, routing requests to the appropriate services within the cluster. Ingress also provides an opportunity to apply security measures, such as TLS termination, authentication, and access control, to ensure secure communication. SSL/ TLS Certificates are commonly used at the Ingress to secure inbound web traffic or external connections to Kubernetes services. By configuring Ingress rules, administrators can enforce security policies and protect the cluster from unauthorized access or malicious traffic.
Ingress does not mirror network traffic by default. Its primary purpose is to route incoming requests to the appropriate services within a Kubernetes cluster. However, some advanced ingress controllers, like Nginx Ingress, support the mirroring of network traffic as an additional feature. This mirroring capability allows administrators to duplicate incoming traffic to a separate destination for analysis or testing purposes without impacting the actual traffic flow to the intended services.
5. Features of Kubernetes
Kubernetes provides a robust feature set that encompasses a wide range of capabilities for running containers and associated infrastructure:
- Storage orchestration: Kubernetes provides flexible storage options, allowing you to mount persistent volumes to Pods. This enables stateful applications to store and access data persistently, even if the underlying Pod is terminated or rescheduled to a different node.
- Secrets and configuration management: Kubernetes provides a secure way to manage sensitive information such as passwords, API keys, and TLS certificates through its Secrets mechanism. It also supports configuration management using ConfigMaps, which can be used to store and manage application configurations.
- Rolling updates and rollbacks: Kubernetes supports rolling updates, allowing you to update your application without downtime by gradually replacing old Pods with new ones. In case of issues, Kubernetes facilitates rollbacks to the previous stable version of the application.
- Multi-tenancy and resource isolation: Kubernetes allows you to create multiple namespaces, which provide logical separation and isolation for different applications or teams within a cluster. Each namespace can have its own set of resources and access controls.
- Monitoring and logging: Kubernetes integrates with various monitoring and logging solutions, making it easier to collect and analyze metrics, logs, and events from your cluster and applications.
- Extensibility: Kubernetes is highly extensible and customizable. It offers an extensive set of APIs, allowing you to extend its functionality or integrate with other systems. You can create custom resources, controllers, and operators to manage and automate complex application workflows.
6. Benefits of Kubernetes
Kubernetes offers numerous benefits for container orchestration and application management. Here are five key benefits of using Kubernetes:
- Scalability and Elasticity: Kubernetes supports horizontal scaling, which lets you grow your applications by introducing or removing Pods on demand. To ensure effective utilization, it automatically distributes the workload across the available resources. With auto-scaling, Kubernetes can flexibly modify the number of Pods based on specified metrics, allowing it to cope with spikes in workload or increased traffic.
- High Availability and Fault Tolerance: Kubernetes has the ability to self-heal, ensuring that applications continue to run even in the face of errors. It reschedules failed or unresponsive containers on healthy nodes after automatically restarting them. Kubernetes provides fault tolerance and redundancy by duplicating Pods across several nodes, lowering the likelihood of downtime.
- Simplified Deployment and Management: Kubernetes simplifies the deployment and management of containerized applications. It abstracts away the complexity of running and coordinating containers, providing a unified platform for deploying, scaling, and updating applications. With declarative configuration management, you define the desired state of your application, and Kubernetes ensures that the actual state matches the desired state, handling the details of application deployment and infrastructure management.
- Service Discovery and Load Balancing: Kubernetes includes built-in service discovery mechanisms, allowing containers to discover and communicate with each other easily. It provides a virtual IP address and DNS name for services, abstracting the underlying Pods. Kubernetes also offers load balancing to distribute network traffic across multiple Pods, ensuring efficient resource utilization and providing fault tolerance for your applications.
- Portability and Flexibility: Kubernetes promotes application portability and flexibility. It abstracts the underlying infrastructure, allowing applications to be deployed consistently across different environments, whether it’s on-premises, in the cloud, or in hybrid setups. Kubernetes supports a wide range of container runtimes, enabling you to choose the most suitable runtime for your applications. Additionally, Kubernetes offers a rich ecosystem of extensions, plugins, and integrations, allowing you to customize and extend its functionality according to your specific needs.
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