Concepts

Detailed explanations of Kubernetes system concepts and abstractions.

Edit This Page

What is Kubernetes?

This page is an overview of Kubernetes.

Kubernetes is an open-source platform for automating deployment, scaling, and operations of application containers across clusters of hosts, providing container-centric infrastructure.

With Kubernetes, you are able to quickly and efficiently respond to customer demand:

Our goal is to foster an ecosystem of components and tools that relieve the burden of running applications in public and private clouds.

Kubernetes is:

Google started the Kubernetes project in 2014. Kubernetes builds upon a decade and a half of experience that Google has with running production workloads at scale, combined with best-of-breed ideas and practices from the community.

Why containers?

Looking for reasons why you should be using containers?

Why Containers?

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:

Why do I need Kubernetes and what can it do?

At a minimum, Kubernetes can schedule and run application containers on clusters of physical or virtual machines. However, Kubernetes also allows developers to ‘cut the cord’ to physical and virtual machines, moving from a host-centric infrastructure to a container-centric infrastructure, which provides the full advantages and benefits inherent to containers. Kubernetes provides the infrastructure to build a truly container-centric development environment.

Kubernetes satisfies a number of common needs of applications running in production, such as:

This provides the simplicity of Platform as a Service (PaaS) with the flexibility of Infrastructure as a Service (IaaS), and facilitates portability across infrastructure providers.

How is Kubernetes 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 empower users to organize their resources however they please. 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 is built upon the same APIs that are available to developers and users. Users can write their own controllers, such as schedulers, with their own APIs that can be targeted by a general-purpose command-line tool.

This design has enabled a number of other systems to build atop Kubernetes.

What Kubernetes is not

Kubernetes is not a traditional, all-inclusive PaaS (Platform as a Service) system. It preserves user choice where it is important.

Kubernetes:

On the other hand, a number of PaaS systems run on Kubernetes, such as Openshift, Deis, and Eldarion. You can also roll your own custom PaaS, integrate with a CI system of your choice, or use only Kubernetes by deploying your container images on Kubernetes.

Since Kubernetes operates at the application 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.

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; the approach is more akin to choreography. This results in a system that is easier to use and more powerful, robust, resilient, and extensible.

What does Kubernetes mean? K8s?

The name Kubernetes originates from Greek, meaning helmsman or pilot, and is the root of governor and cybernetic. K8s is an abbreviation derived by replacing the 8 letters “ubernete” with “8”.

What’s next

Analytics

Create an Issue Edit this Page