Kubernetes is a portable, extensible, open source platform for managing containerized workloads and services, that facilitates both declarative configuration and automation. It has a large, rapidly growing ecosystem. Kubernetes services, support, and tools are widely available.
This page is an overview of Kubernetes.
Kubernetes is a portable, extensible, open source platform for managing containerizedworkloads and services, that facilitates both declarative configuration and automation.It has a large, rapidly growing ecosystem. Kubernetes services, support, and tools are widely available.
The name Kubernetes originates from Greek, meaning helmsman or pilot. K8s as an abbreviationresults from counting the eight letters between the "K" and the "s". Google open-sourced theKubernetes project in 2014. Kubernetes combinesover 15 years of Google's experience runningproduction workloads at scale with best-of-breed ideas and practices from the community.
Going back in time
Let's take a look at why Kubernetes is so useful by going back in time.
Traditional deployment era:Early on, organizations ran applications on physical servers. There was no way to defineresource boundaries for applications in a physical server, and this caused resourceallocation issues. For example, if multiple applications run on a physical server, therecan be instances where one application would take up most of the resources, and as a result,the other applications would underperform. A solution for this would be to run each applicationon a different physical server. But this did not scale as resources were underutilized, and itwas expensive for organizations to maintain many physical servers.
Virtualized deployment era: As a solution, virtualization was introduced. It allows youto run multiple Virtual Machines (VMs) on a single physical server's CPU. Virtualizationallows applications to be isolated between VMs and provides a level of security as theinformation of one application cannot be freely accessed by another application.
Virtualization allows better utilization of resources in a physical server and allowsbetter scalability because an application can be added or updated easily, reduceshardware costs, and much more. With virtualization you can present a set of physicalresources as a cluster of disposable virtual machines.
Each VM is a full machine running all the components, including its own operatingsystem, on top of the virtualized hardware.
Container deployment era: Containers are similar to VMs, but they have relaxedisolation properties to share the Operating System (OS) among the applications.Therefore, containers are considered lightweight. Similar to a VM, a containerhas its own filesystem, share of CPU, memory, process space, and more. As theyare decoupled from the underlying infrastructure, they are portable across cloudsand OS distributions.
Containers have become popular because they provide extra benefits, such as:
- Agile application creation and deployment: increased ease and efficiency ofcontainer image creation compared to VM image use.
- Continuous development, integration, and deployment: provides for reliableand frequent container image build and deployment with quick and efficientrollbacks (due to image immutability).
- Dev and Ops separation of concerns: create application container images atbuild/release time rather than deployment time, thereby decouplingapplications from infrastructure.
- Observability: not only surfaces OS-level information and metrics, but alsoapplication health and other signals.
- Environmental consistency across development, testing, and production: runsthe same on a laptop as it does in the cloud.
- Cloud and OS distribution portability: runs on Ubuntu, RHEL, CoreOS, on-premises,on major public clouds, and anywhere else.
- Application-centric management: raises the level of abstraction from running anOS on virtual hardware to running an application on an OS using logical resources.
- Loosely coupled, distributed, elastic, liberated micro-services: applications arebroken into smaller, independent pieces and can be deployed and managed dynamically –not a monolithic stack running on one big single-purpose machine.
- Resource isolation: predictable application performance.
- Resource utilization: high efficiency and density.
Why you need Kubernetes and what it can do
Containers are a good way to bundle and run your applications. In a productionenvironment, you need to manage the containers that run the applications andensure that there is no downtime. For example, if a container goes down, anothercontainer needs to start. Wouldn't it be easier if this behavior was handled by a system?
That's how Kubernetes comes to the rescue! Kubernetes provides you with a frameworkto run distributed systems resiliently. It takes care of scaling and failover foryour application, provides deployment patterns, and more. For example: Kubernetescan easily manage a canary deployment for your system.
Kubernetes provides you with:
- Service discovery and load balancingKubernetes 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 distributethe network traffic so that the deployment is stable.
- Storage orchestrationKubernetes allows you to automatically mount a storage system of your choice, such aslocal storages, public cloud providers, and more.
- Automated rollouts and rollbacksYou 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 yourdeployment, remove existing containers and adopt all their resources to the new container.
- Automatic bin packingYou 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 fitcontainers onto your nodes to make the best use of your resources.
- Self-healingKubernetes restarts containers that fail, replaces containers, kills containers that don'trespond to your user-defined health check, and doesn't advertise them to clients until theyare ready to serve.
- Secret and configuration managementKubernetes lets you store and manage sensitive information, such as passwords, OAuth tokens,and SSH keys. You can deploy and update secrets and application configuration withoutrebuilding your container images, and without exposing secrets in your stack configuration.
- Batch executionIn addition to services, Kubernetes can manage your batch and CI workloads, replacing containers that fail, if desired.
- Horizontal scalingScale your application up and down with a simple command, with a UI, or automatically based on CPU usage.
- IPv4/IPv6 dual-stackAllocation of IPv4 and IPv6 addresses to Pods and Services
- Designed for extensibilityAdd features to your Kubernetes cluster without changing upstream source code.
What Kubernetes is not
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 asdeployment, scaling, load balancing, and lets users integrate their logging, monitoring,and alerting solutions. However, Kubernetes is not monolithic, and these default solutionsare optional and pluggable. Kubernetes provides the building blocks for building developerplatforms, but preserves user choice and flexibility where it is important.
Kubernetes:
- Does not limit the types of applications supported. Kubernetes aims to support anextremely diverse variety of workloads, including stateless, stateful, and data-processingworkloads. If an application can run in a container, it should run great on Kubernetes.
- Does not deploy source code and does not build your application. Continuous Integration,Delivery, and Deployment (CI/CD) workflows are determined by organization cultures andpreferences as well as technical requirements.
- Does not provide application-level services, such as middleware (for example, message buses),data-processing frameworks (for example, Spark), databases (for example, MySQL), caches, norcluster storage systems (for example, Ceph) as built-in services. Such components can run onKubernetes, and/or can be accessed by applications running on Kubernetes through portablemechanisms, such as the Open Service Broker.
- Does not dictate logging, monitoring, or alerting solutions. It provides some integrationsas proof of concept, and mechanisms to collect and export metrics.
- Does not provide nor mandate a configuration language/system (for example, Jsonnet). It providesa declarative API that may be targeted by arbitrary forms of declarative specifications.
- 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 needfor orchestration. The technical definition of orchestration is execution of a defined workflow:first do A, then B, then C. In contrast, Kubernetes comprises a set of independent, composablecontrol 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. Thisresults in a system that is easier to use and more powerful, robust, resilient, and extensible.
What's next
- Take a look at the Kubernetes Components
- Take a look at the The Kubernetes API
- Take a look at the Cluster Architecture
- Ready to Get Started?