Table of contents
Kubernetes is a portable, extensible, open-source platform for managing containerized workloads and services, that facilitates both declarative configuration and automation. Google open-sourced the Kubernetes project in 2014.
The name Kubernetes has origins in Greek, meaning helmsman or pilot. K8s is an abbreviation that results from counting the eight letters between the "K" and the "s".
Kubernetes combines over 15 years of Google's experience running production workloads at scale with best-of-breed ideas and practices from the community.
A little History
Traditional Deployment Era
Earlier, organizations ran applications on physical servers and there was no way to define resource boundaries for applications on the physical servers.
There were instances where one application would take up most of the resources and as a result, other applications would underperform. To prevent this, each application was run on a separate physical server. It has expensive to scale up.
Virtualized Deployment Era
Virtualization was introduced as a solution to the physical server problem. It allowed you to run multiple Virtual Machines (VMs) on a single physical server's CPU.
Virtualization even allowed applications to be isolated between VMs and provided a level of security as the information/data could not be accessed freely by another application.
It made better utilization of resources of a physical server and better scalability because applications could be added or updated easily.
Virtualization even reduces hardware costs as with virtualization, you can present a set of physical resources as a cluster of disposable virtual machines. Each VM is a full machine running all the components, including its own OS, on top of virtualized hardware.
Container Deployment Era
Containers are similar to VMs but have relaxed isolation properties to share the Operating System among the applications due to which containers are considered lightweight.
A container, similar to VM has its own filesystem, the share of CPU, memory, process space, and more but since they are decoupled from the underlying infrastructure, they are portable across clouds and OS distributions. You can read more about containers in my blog here
Need for Kubernetes
Containers are a good way to bundle and run your applications but in a production environment, you will need to manage the containers that run your application to ensure that there is no downtime. If a container goes down, another container needs to be started.
Kubernetes provides you with a framework to run distributed systems resiliently. It takes care of scaling and failover for your application, provides deployment patterns, and more.
Feature of Kubernetes
Kubernetes provides you with:
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.
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
You can describe the desired state for your deployed containers using Kubernetes, and it can change the actual state to the desired state at a controlled rate.
For example, you can automate Kubernetes to create new containers for your deployment, remove existing containers and adopt all their resources to the new container.
Automatic bin packing
You provide Kubernetes with a cluster of nodes that it can use to run containerized tasks. You tell Kubernetes how much CPU and memory (RAM) each container needs. Kubernetes can fit containers onto your nodes to make the best use of your resources.
Kubernetes restarts containers that fail, replaces containers, kills containers that don't respond to your user-defined health check, and doesn't advertise them to clients until they are ready to serve.
Secret and configuration management
Kubernetes let you store and manage sensitive information, such as passwords, OAuth tokens, and SSH keys. You can deploy and update secrets and application configuration without rebuilding your container images, and without exposing secrets in your stack configuration
What Kubernetes does not provide
Kubernetes is not a traditional, all-inclusive PaaS(Platform as a Service) system.
Since Kubernetes operates at the container level rather than at the hardware level, it provides some generally applicable features common to PaaS offerings, such as deployment, scaling, and load balancing, and lets users integrate their logging, monitoring, and alerting solutions. However, Kubernetes is not monolithic, and these default solutions are optional and pluggable. Kubernetes provides the building blocks for building developer platforms but preserves user choice and flexibility where it is important.
It does not limit the types of applications supported. Kubernetes aims to support an extremely diverse variety of workloads, including stateless, stateful, and data-processing workloads. If an application can run in a container, it should run great on Kubernetes.
It does not deploy source code and does not build your application. Continuous Integration, Delivery, and Deployment (CI/CD) workflows are determined by organization cultures and preferences as well as technical requirements.
It does not provide application-level services, such as middleware (for example, message buses), data-processing frameworks (for example, Spark), databases (for example, MySQL), caches, or clusters storage systems (for example, Ceph) as built-in services. Such components can run on Kubernetes, and/or can be accessed by applications running on Kubernetes through portable mechanisms, such as the Open Service Broker.
It does not dictate logging, monitoring, or alerting solutions. It provides some integrations as proof of concept, and mechanisms to collect and export metrics. Does not provide nor mandate a configuration language/system (for example, Jsonnet). It provides a declarative API that may be targeted by arbitrary forms of declarative specifications.
It does not provide nor adopt any comprehensive machine configuration, maintenance, management, or self-healing systems.
Additionally, Kubernetes is not a mere orchestration system. In fact, it eliminates the need for orchestration. The technical definition of orchestration is the execution of a defined workflow: first, do A, then B, then C. In contrast, Kubernetes comprises a set of independent, composable control processes that continuously drive the current state towards the provided desired state. It shouldn't matter how you get from A to C. Centralized control is also not required. This results in a system that is easier to use and more powerful, robust, resilient, and extensible.
This is the introductory guide to Kubernetes, just to know what Kubernetes it, we will deep dive into Kubernetes in the consecutive blog of the Kubernetes series.