Kubernetes is an open-source container orchestration system. It was developed by Google and is now maintained by the Cloud Native Computing Foundation (CNCF). It is designed to automate the deployment, scaling, and management of containerized applications.
At a high level, Kubernetes works by managing a cluster of machines (often called “nodes”) and scheduling the running of containerized applications (often called “pods”) on those nodes. A pod is the smallest and simplest unit in the Kubernetes object model and it represents a single instance of a running process in your application. Pods can contain one or more containers and they can share storage resources and network interfaces.
A declarative approach is used to manage the desired state of your applications, meaning that you define how you want your applications to be running, and the Kubernetes engine will make sure that the actual state of the applications match your desired state. The desired state is defined using Kubernetes objects, such as pods, services, and deployments.
Services, for example, are used to expose your pods to the outside world. They provide a stable endpoint for external clients to access your pods. Services also load balance traffic between the pods that match a certain selector.
Deployments, on the other hand, are used to manage the desired state of your applications. They allow you to declare how many replicas of your pods should be running, and Kubernetes will automatically ensure that this number is met. If a pod goes down, Kubernetes will automatically create a new one to replace it.
Built-in features for scaling applications are provided. By adjusting the number of replicas in a deployment, it is simple to scale an application up or down. The system will automatically create or delete pods to match the desired number of replicas.
Kubernetes also provides built-in features for managing and monitoring your applications. You can view the status of your applications, get metrics and logs, and even access a shell inside a running container.
Additionally, Kubernetes provides a variety of storage options to manage the data of your applications. Persistent Volumes (PVs) and Persistent Volume Claims (PVCs) are used to provide storage for your pods, allowing your pods to retain data even if they are deleted or recreated.
Kubernetes also has built-in support for rolling updates, which allows you to update your applications without any downtime. You can update your application by defining a new version of the container image in your deployment and Kubernetes will automatically roll out the updates to your pods in a controlled manner, ensuring that there’s always a healthy set of pods running.
Another important feature of Kubernetes is its support for automatic service discovery and load balancing. Services in Kubernetes are automatically assigned a unique IP address, and the DNS name is automatically created for them. This allows for easy communication between different parts of your application. Kubernetes also provides built-in load balancing for services, which routes the traffic to the available pods.
Kubernetes also supports Namespaces, which are used to separate resources within a cluster. Namespaces can be used to isolate resources, so that different teams or environments can have their own resources without interfering with each other.
Finally, Kubernetes also has a built-in security model. It supports role-based access control (RBAC) and network policies that allow you to control who can access your resources and what actions they can perform. Kubernetes also supports Pod Security Policies, which can be used to enforce security constraints on pods.
In summary, Kubernetes provides a powerful set of features for automating the deployment, scaling, and management of containerized applications. It has a declarative approach to manage the desired state of your applications, built-in features for scaling, automatic service discovery and load balancing, support for rolling updates and storage options, Namespaces and built-in security model. It is a robust and widely adopted platform that can help Java/Spring developers to deploy and manage their applications in a more efficient and effective way.