Kubernetes, also known as K8s, is an open-source container orchestration platform. It automates the deployment, scaling, and management of containerized applications. Kubernetes provides a powerful API for managing the lifecycle of containers and the infrastructure on which they run. It’s a distributed system that runs on a cluster of machines.
Kubernetes Architecture
At its core, Kubernetes is a distributed system that runs on a cluster of machines. A Kubernetes cluster consists of one or more master nodes and one or more worker nodes. The master node is responsible for managing the cluster’s state and scheduling tasks, while the worker nodes are responsible for running the containers.
The Kubernetes API is exposed through a set of RESTful endpoints that can be accessed by clients such as the kubectl command-line tool, Kubernetes Dashboard, or any other custom client that can interact with the API.
Kubernetes uses a declarative approach to managing resources, where you define the desired state of your application, and Kubernetes will take care of bringing the actual state in line with the desired state.
Pods
A pod is the smallest deployable unit in Kubernetes. It represents a single instance of a running process in a container. A pod can contain one or more containers, which share the same network namespace and can communicate with each other over localhost.
Pods are designed to be ephemeral and disposable. They can be easily created and destroyed as needed, and their lifespan is typically tied to the lifespan of the process or task that they are running.
Pods are scheduled onto worker nodes by the Kubernetes scheduler, which takes into account various factors such as resource constraints, affinity and anti-affinity rules, and node labels and taints.
Replication Controllers
A replication controller is responsible for ensuring that a specified number of replicas (i.e., copies) of a pod are running at all times. If a pod fails or is terminated, the replication controller will automatically create a new one to replace it.
Replication controllers use a simple label-based selector to match pods to their desired state. For example, you could define a replication controller to ensure that three replicas of a web server pod are always running.
Services
A service is an abstraction layer that provides a stable IP address and DNS name for a set of pods, making it easy to access the application from other parts of the cluster or from outside the cluster.
Services can also provide load balancing and traffic routing capabilities. For example, you could define a service to distribute incoming traffic across multiple replicas of a web server pod.
Deployments
A deployment is a higher-level abstraction that provides declarative updates to pods and replication controllers. It allows you to define a desired state for your application, and Kubernetes will automatically perform rolling updates to ensure that the actual state matches the desired state.
Deployments use a rolling update strategy by default, which means that Kubernetes will gradually update the replicas of a pod one by one, ensuring that there is always a minimum number of replicas running during the update process.
ConfigMaps and Secrets
ConfigMaps and Secrets are Kubernetes objects that allow you to manage configuration data and sensitive information such as passwords and API keys.
ConfigMaps can be used to store configuration data that can be accessed by your application. For example, you could define a ConfigMap to store a list of environment variables that your application needs to run.
Secrets are similar to ConfigMaps, but they are designed to store sensitive data that should not be exposed to the application or the cluster. Secrets are stored encrypted in etcd, the Kubernetes key-value store.
Volumes
Volumes are Kubernetes objects that allow you to provide persistent storage to your containers. Volumes can be created from a variety of storage options, such as local disks, network-attached storage (NAS), and cloud storage. Volumes are mounted into a container’s filesystem, allowing the container to read and write data to the volume.
Conclusion
Kubernetes is a powerful platform that allows developers and operations teams to easily deploy, manage, and scale containerized applications. It provides a declarative approach to managing resources and automates many of the tasks involved in running a distributed system. Kubernetes is designed to be flexible and can be used with a wide variety of container runtimes and cloud providers. With its robust API, powerful scheduling system, and support for advanced features such as auto-scaling and rolling updates, Kubernetes has become the de facto standard for container orchestration. Whether you’re running a small microservice application or a large-scale distributed system, Kubernetes can help you streamline your deployment process and improve your application’s reliability and availability.