Updates the What is Kubernetes page (#14657)

* Updates the What is Kubernetes page

* Adds content to the what is kubernetes used for section.

* Updates the ordered list.

* Formats the content.

* Update the content as per the comments

* Fix a broken link

content/en/docs/concepts/overview/what-is-kubernetes.md

@@ -5,7 +5,7 @@ reviewers:
 title: What is Kubernetes
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@@ -15,196 +15,77 @@ This page is an overview of Kubernetes.
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-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.
+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.
 
-Google open-sourced the Kubernetes project in 2014. Kubernetes builds upon
-a [decade and a half of experience that Google has with running
-production workloads at
-scale](https://research.google.com/pubs/pub43438.html), combined with
-best-of-breed ideas and practices from the community.
+The name Kubernetes originates from Greek, meaning helmsman or pilot. Google open-sourced the Kubernetes project in 2014. Kubernetes builds upon a [decade and a half of experience that Google has with running production workloads at scale](https://ai.google/research/pubs/pub43438), combined 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.
+
+![Deployment evolution](/images/docs/Container_Evolution.svg)
+
+**Traditional deployment era:**
+Early on, organizations ran applications on physical servers. There was no way to define resource boundaries for applications in a physical server, and this caused resource allocation issues. For example, if multiple applications run on a physical server, there can 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 application on a different physical server. But this did not scale as resources were underutilized, and it was expensive for organizations to maintain many physical servers.
+
+**Virtualized deployment era:**  As a solution, virtualization was introduced. It allows you to run multiple Virtual Machines (VMs) on a single physical server's CPU. Virtualization allows applications to be isolated between VMs and provides a level of security as the information of one application cannot be freely accessed by another application.
+
+Virtualization allows better utilization of resources in a physical server and allows better scalability because an application can be added or updated easily, reduces hardware costs, and much more.
+
+Each VM is a full machine running all the components, including its own operating system, on top of the virtualized hardware.
+
+**Container deployment era:** Containers are similar to VMs, but they have relaxed isolation properties to share the Operating System (OS) among the applications. Therefore, containers are considered lightweight. Similar to a VM, a container has its own filesystem, CPU, memory, process space, and more. As they are decoupled from the underlying infrastructure, they are portable across clouds and OS distributions.
+
+Containers are becoming popular because they have many benefits. Some of the container benefits are listed below:
+
+* Agile application creation and deployment: Increased ease and efficiency of container image creation compared to VM image use.
+* Continuous development, integration, and deployment: Provides for reliable and frequent container image build and deployment with quick and easy rollbacks (due to image immutability).
+* Dev and Ops separation of concerns: Create application container images at build/release time rather than deployment time, thereby decoupling applications from infrastructure.
+* Observability not only surfaces OS-level information and metrics, but also application health and other signals.
+* Environmental consistency across development, testing, and production: Runs the same on a laptop as it does in the cloud.
+* Cloud and OS distribution portability: Runs on Ubuntu, RHEL, CoreOS, on-prem, Google Kubernetes Engine, and anywhere else.
+* Application-centric management: Raises the level of abstraction from running an OS on virtual hardware to running an application on an OS using logical resources.
+* Loosely coupled, distributed, elastic, liberated micro-services: Applications are broken 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 do I need Kubernetes and what can it do
 
-Kubernetes has a number of features. It can be thought of as:
-
-- a container platform
-- a microservices platform
-- a portable cloud platform
-and a lot more.
-
-Kubernetes provides a **container-centric** management environment. It
-orchestrates computing, networking, and storage infrastructure on
-behalf of user workloads. This provides much of the simplicity of
-Platform as a Service (PaaS) with the flexibility of Infrastructure as
-a Service (IaaS), and enables portability across infrastructure
-providers.
-
-## How Kubernetes is a platform
-
-Even though Kubernetes provides a lot of functionality, there are
-always new scenarios that would benefit from new
-features. Application-specific workflows can be streamlined to
-accelerate developer velocity. Ad hoc orchestration that is acceptable
-initially often requires robust automation at scale. This is why
-Kubernetes was also designed to serve as a platform for building an
-ecosystem of components and tools to make it easier to deploy, scale,
-and manage applications.
-
-[Labels](/docs/concepts/overview/working-with-objects/labels/) empower
-users to organize their resources however they
-please. [Annotations](/docs/concepts/overview/working-with-objects/annotations/)
-enable users to decorate resources with custom information to
-facilitate their workflows and provide an easy way for management
-tools to checkpoint state.
-
-Additionally, the [Kubernetes control
-plane](/docs/concepts/overview/components/) is built upon the same
-[APIs](/docs/reference/using-api/api-overview/) that are available to developers
-and users. Users can write their own controllers, such as
-[schedulers](https://github.com/kubernetes/community/blob/{{< param "githubbranch" >}}/contributors/devel/scheduler.md),
-with [their own
-APIs](/docs/concepts/api-extension/custom-resources/)
-that can be targeted by a general-purpose [command-line
-tool](/docs/user-guide/kubectl-overview/).
-
-This
-[design](https://git.k8s.io/community/contributors/design-proposals/architecture/architecture.md)
-has enabled a number of other systems to build atop Kubernetes.
+Containers are a good way to bundle and run your applications. In a production environment, you need to manage the containers that run the applications and ensure that there is no downtime. For example, if a container goes down, another container needs to restart. 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 framework to run distributed systems resiliently. It takes care of your scaling requirements, failover, deployment patterns, and more. For example, Kubernetes can easily manage a canary deployment for your system.
+
+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.
+* **Storage orchestration**  
+Kubernetes allows you to automatically mount a storage system of your choice, such as local storages, 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**  
+Kubernetes allows you to specify how much CPU and memory (RAM) each container needs. When containers have resource requests specified, Kubernetes can make better decisions to manage the resources for containers.
+* **Self-healing**  
+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 lets 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 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 as deployment,
-scaling, load balancing, logging, and monitoring. 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.
+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, load balancing, logging, and monitoring. 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.
 
 Kubernetes:
 
-* 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.
-* 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.
-* Does not provide application-level services, such as middleware
-  (e.g., message buses), data-processing frameworks (for example,
-  Spark), databases (e.g., mysql), caches, nor cluster storage systems (e.g.,
-  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.
-* 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 (e.g.,
-  [jsonnet](https://github.com/google/jsonnet)). It provides a 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 need for orchestration. The technical
-definition of *orchestration* is execution of a defined workflow:
-first do A, then B, then C. In contrast, Kubernetes is comprised of 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.
-
-## Why containers
-
-Looking for reasons why you should be using containers?
-
-![Why Containers?](/images/docs/why_containers.svg)
-
-The *Old Way* to deploy applications was to install the applications
-on a host using the operating-system package manager. This had the
-disadvantage of entangling the applications' executables,
-configuration, libraries, and lifecycles with each other and with the
-host OS. One could build immutable virtual-machine images in order to
-achieve predictable rollouts and rollbacks, but VMs are heavyweight
-and non-portable.
-
-The *New Way* is to deploy containers based on operating-system-level
-virtualization rather than hardware virtualization. These containers
-are isolated from each other and from the host: they have their own
-filesystems, they can't see each others' processes, and their
-computational resource usage can be bounded. They are easier to build
-than VMs, and because they are decoupled from the underlying
-infrastructure and from the host filesystem, they are portable across
-clouds and OS distributions.
-
-Because containers are small and fast, one application can be packed
-in each container image. This one-to-one application-to-image
-relationship unlocks the full benefits of containers. With containers,
-immutable container images can be created at build/release time rather
-than deployment time, since each application doesn't need to be
-composed with the rest of the application stack, nor married to the
-production infrastructure environment. Generating container images at
-build/release time enables a consistent environment to be carried from
-development into production.  Similarly, containers are vastly more
-transparent than VMs, which facilitates monitoring and
-management. This is especially true when the containers' process
-lifecycles are managed by the infrastructure rather than hidden by a
-process supervisor inside the container. Finally, with a single
-application per container, managing the containers becomes tantamount
-to managing deployment of the application.
-
-Summary of container benefits:
-
-* **Agile application creation and deployment**:
-    Increased ease and efficiency of container image creation compared to VM image use.
-* **Continuous development, integration, and deployment**:
-    Provides for reliable and frequent container image build and
-    deployment with quick and easy rollbacks (due to image
-    immutability).
-* **Dev and Ops separation of concerns**:
-    Create application container images at build/release time rather
-    than deployment time, thereby decoupling applications from
-    infrastructure.
-* **Observability**
-    Not only surfaces OS-level information and metrics, but also application
-    health and other signals.
-* **Environmental consistency across development, testing, and production**:
-    Runs the same on a laptop as it does in the cloud.
-* **Cloud and OS distribution portability**:
-    Runs on Ubuntu, RHEL, CoreOS, on-prem, Google Kubernetes Engine, and anywhere else.
-* **Application-centric management**:
-    Raises the level of abstraction from running an OS on virtual
-    hardware to running an application on an OS using logical resources.
-* **Loosely coupled, distributed, elastic, liberated [micro-services](https://martinfowler.com/articles/microservices.html)**:
-    Applications are broken 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.
-
-## What Kubernetes and K8s mean
-
-The name **Kubernetes** originates from Greek, meaning *helmsman* or
-*pilot*, and is the root of *governor* and
-[cybernetic](http://www.etymonline.com/index.php?term=cybernetics). *K8s*
-is an abbreviation derived by replacing the 8 letters "ubernete" with
-"8".
+* 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.
+* 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.
+* Does not provide application-level services, such as middleware (for example, message buses), data-processing frameworks (for example, Spark), databases (for example, mysql), caches, nor cluster 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.
+* 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.
+* 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 execution of a defined workflow: first do A, then B, then C. In contrast, Kubernetes is comprised of 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.
 
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+*   Take a look at the [Kubernetes Components](/docs/concepts/overview/components/)
 *   Ready to [Get Started](/docs/setup/)?
-*   For more details, see the [Kubernetes Documentation](/docs/home/).
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-
-