Kubernetes Overview

Kubernetes is a portable, extensible, open-source platform for managing containerized workloads and services, that facilitates both declarative configuration and automation.

Kubernetes originates from Greek, meaning helmsman or pilot.
Kubernetes provides an orchestration framework to run distributed systems resiliently. It takes care of scaling and failover for the application, provides deployment patterns, and more.

Container Deployment Model

Deployment evolution

Containers are similar to VMs, but they have relaxed isolation properties to share the Operating System (OS) among the applications.
Containers are lightweight and have their own filesystem, share of CPU, memory, process space, and more.

Containers are decoupled from the underlying infrastructure, they are portable across clouds and OS distributions.
Containers provide the following benefits
- Agile application creation and deployment
- Continuous development, integration, and deployment
- Dev and Ops separation of concerns
- Observability
- Environmental consistency across development, testing, and production
- Cloud and OS distribution portability
- Application-centric management
- Loosely coupled, distributed, elastic, liberated micro-services
- Resource isolation & utilization

Service discovery and load balancing
- Kubernetes can expose a container using the DNS name or using their own IP address.
- If traffic to a container is high, Kubernetes is able to load balance and distribute the network traffic so that the deployment is stable.
Storage orchestration
- Kubernetes allows you to automatically mount a storage system of your choice, such as local storage, public cloud providers, and more.
Automated rollouts and rollbacks
- Kubernetes can change the actual state of the deployed containers to the desired state at a controlled rate ensuring zero downtime.

Automatic bin packing
- Kubernetes can fit containers onto the available nodes to make the best use of the resources as per the specified container specification.
Self-healing & High Availability
- Kubernetes restarts containers that fail, replaces containers, kills containers that don’t respond to the user-defined health check, and doesn’t advertise them to clients until they are ready to serve.
Scalability
- Kubernetes can help scale the application as per the load.

Secret and configuration management
- Kubernetes helps store and manage sensitive information, such as passwords, OAuth tokens, and SSH keys.
- Secrets and application configuration can be deployed without rebuilding the container images, and without exposing secrets in the stack configuration.

Refer to detailed blog post @ Kubernetes Architecture

Kubernetes Architecture Master components

Master components make global decisions about the cluster (for example, scheduling), and that they detect and answer cluster events (for example, beginning a replacement pod when a deployment’s replicas field is unsatisfied).
Master components include
- Kube-API server – Exposes the API.
- Etcd – key-value stores all cluster data. (Can be run on the same server as a master node or on a dedicated cluster.)
- Kube-scheduler – Schedules new pods on worker nodes.
- Kube-controller-manager – Runs the controllers.
- Cloud-controller-manager – Talks to cloud providers.

Node components run on every node, maintaining running pods and providing the Kubernetes runtime environment.
- Kubelet – Agent that ensures containers in a pod are running.
- Kube-proxy – Keeps network rules and performs forwarding.
- Container runtime – Runs containers.

Refer to blog post @ Kubernetes Security