Let's start with the basics. Kubernetes is an open-source platform designed to automate deploying, scaling, and operating application containers. It allows you to manage a cluster of containers as a single system, making it easier to manage and scale your applications.
In our example, we'll use a JavaScript application with a database. Kubernetes will help us deploy and manage these components in a scalable and reliable way.
We'll cover how to create and manage Kubernetes resources like Pods, Services, Deployments, ConfigMaps, volumes, Deployment and Statefulset. By the end of this journey, you'll have a good understanding of how Kubernetes works and how it can benefit your applications.
Node and Pods
In Kubernetes (often abbreviated as K8s), we work with nodes (servers) and pods (containers), a "node" refers to a physical or virtual machine that is part of a cluster. Nodes are the computational units that run your applications. Each node can be a standalone server or a virtual machine, and it typically runs a container runtime, such as Docker
Pods are like a layer on top of containers, abstracting away the underlying technology. Each pod typically runs one main application container, but you can have additional helper containers. Kubernetes provides a virtual network, giving each pod its own internal IP address for communication.
Service and Ingres
Now, pods can be ephemeral—they might die and get replaced, leading to a new IP address. To solve this, Kubernetes introduces services, offering a stable IP address for pods. This stability is crucial for communication, especially when pods restart. Lifecycle of pod and service is not connected so even if the pod dies, the service and it's IP address will stay.
For external access of your application, there are external services, while internal services protect sensitive components from public access like Database. Apparently, the URL of external service is not very practical (my-app-services-ip:port).To make URLs more practical, Kubernetes uses Ingress, forwarding requests to the appropriate service.
Configmap and Secret
When dealing with configuration changes, Kubernetes has Config Maps. They store external configurations, like database URLs, allowing updates without rebuilding the entire application.External configuration of your application usually contains configuration data like - URL, or some other services you use. In K8s you just connect your configmap to pod gets the data that configmap contains.So now you just have to adjust the configmap and nothing else.
NOTE : DON'T put credentials into configmap. So for this purpose, kubernetes has another component i.e. secret is used.
Sensitive data, such as credentials, is handled by Secrets. These are like Config Maps but are designed for secure information and stored in base64 encoding. Encryption tools add an extra layer of security.Just like configmap, secret is also connected to pod.
Config Maps and Secrets seamlessly integrate into application pods as environmental variables or properties, enabling dynamic adjustments without extensive rebuilding.
Volumes
In the world of containerized applications, the need for persistent storage is inevitable. Kubernetes addresses this requirement through Volumes. A Volume in Kubernetes is essentially a directory accessible to containers in a Pod, providing a way to store and share data.
Volumes come in various types, each catering to different use cases. For instance, an EmptyDir volume is ephemeral, tied to the lifecycle of a Pod, while a PersistentVolume (PV) can outlive Pod restarts, offering persistent storage that survives even if the Pod is rescheduled to a different node.
Volumes facilitate data sharing among containers within the same Pod, ensuring seamless communication and data persistence across the application's lifecycle.
Deployments in Kubernetes
Deployments in Kubernetes represent a declarative approach to managing application deployments. Defined using YAML manifests, Deployments enable you to describe the desired state of your application, including the number of replicas, container specifications, and update strategies.
By using Deployments, you gain automated rollout and rollback capabilities. Rolling updates, for instance, allow you to smoothly transition from one version of your application to another without downtime. This ensures high availability and minimizes disruptions during updates.
Deployments are a cornerstone of maintaining a healthy and self-healing application environment in Kubernetes, fostering scalability and reliability.
StatefulSets in Kubernetes
While Deployments are excellent for stateless applications, StatefulSets cater to stateful applications that require stable network identities and persistent storage.
StatefulSets introduce ordered deployment and scaling of Pods, ensuring that each Pod has a unique identifier and that Pods are created or replaced in a predictable order. This is crucial for applications like databases, where maintaining a stable network identity is paramount.
StatefulSets, coupled with PersistentVolumes, provide a robust solution for deploying stateful applications in Kubernetes. They are particularly valuable for scenarios where data consistency and ordering are critical.
In conclusion, Volumes, Deployments, and StatefulSets are integral components in the Kubernetes toolkit, each serving a specific purpose in the orchestration of containerized applications. Understanding and harnessing the power of these features is key to building resilient, scalable, and maintainable applications in the dynamic world of Kubernetes.
