<h1>Brief introduction</h1>
Kubernetes is an open source for managing containerized applications on multiple hosts in a cloud platform, Kubernetes' goal is to make deploying containerized applications simple and powerful, Kubernetes provides a mechanism for application deployment, planning, updating, and maintenance.
A core feature of Kubernetes is to be able to manage containers autonomously to ensure that the containers in the cloud platform run according to the user's expectations (for example, the user wants to run Apache all the time, the user does not need to care about how to do it, Kubernetes will automatically monitor, and then to restart, new, in short, let Apache always provide services), the administrator can load a micro service, let the planner to find the right location, at the same time, Kubernetes also improves the tooling and user-friendliness, allowing users to easily deploy their own applications (like canary deployments).
Kubernetes now focuses on uninterrupted service state (such as web servers or cache servers) and cloud-native platform applications (Nosql), and in the near future will support a variety of services in various production cloud platforms, such as batching, workflow, and traditional databases.
In Kubenetes, all containers run in Pods, a Pod can host one or more related containers, and in the later case, containers in the same Pod are deployed on the same physical machine and can share resources. A Pod can also contain O or more disk volume groups (volumes), these volume groups will be provided to a container in the form of a directory, or shared by all the containers in the Pod, for each pod created by the user, the system will automatically select the healthy and sufficient capacity of the machine, and then create a container similar to the container, when the container creation fails, the container will be automatically restarted by the node agent, this node agent is called kubelet, but, If the Pod fails or the machine fails, it will not automatically transfer and start unless the user defines a replication controller.
Users can create and manage their own pods, and Kubernetes simplifies these operations into two operations: deploying multiple pod replicas based on the same Pod profile, and creating alternative Pods when a pod hangs up or the machine hangs up. The part of the Kubernetes API responsible for restarting, migrating, and other behaviors is called the "replication controller", which generates a pod based on a template, and then the system creates many redundancies according to the user's needs, and these redundant pods make up an entire application, or a service, or a layer in the service. Once a Pod is created, the system will constantly monitor the health of the Pod and the health of the host where the Pod is located, if the Pod is hung up due to software reasons or the machine is hung up, the replication controller will automatically create a one-touch Pod on a healthy machine to maintain the original Pod redundancy state unchanged, and multiple Pods in an application can share a machine.
<h1>origin</h1>
Large-scale container cluster management tools, from Borg to Kubernetes
At the same time as Docker's rapid development as an advanced container engine, Google has also begun to contribute to its accumulation of container technology and clusters. Inside Google, container technology has been used for many years, and the Borg system runs and manages thousands of container applications, and with its support, whether it is Google Search, Gmail or Google Maps, it is easy to obtain technical resources from huge data centers to support the operation of services.
Borg is the manager of the cluster, in its system, running a large number of clusters, and each cluster can be composed of thousands of server connections, Borg at all times from many applications submitted hundreds of Jobs, these Jobs to receive, schedule, start, stop, restart and monitor.
As Google's competitive technical advantage, Borg was naturally hidden as a trade secret, but when Tewtter engineers carefully built their own Borg system (Mesos), Google also took the time to introduce new open source tools derived from its own technical theory.
In June 2014, Google cloud computing expert Eric Brewer unveiled the new open source tool at a launch in San Francisco, whose name Kubernetes means captain or navigator in Greek, which coincides with its role in container cluster management, that is, as the commander of many cargo ships loaded with containers, with global scheduling and operational monitoring responsibilities.
Kubernetes takes a higher level of abstraction of computing resources, handing over the final application service to the user by combining containers in a nuanced manner. Kubernetes considered the requirements of container cross-machine connectivity at the beginning of the model, supporting multiple network solutions, and building cluster-wide SDN networks at the service level. The goal is to place service discovery and load balancing within the reach of the container, a transparent way that facilitates communication between services and provides a platform foundation for microservices architecture practices. At the Pod level, as the smallest object that Kubernetes can operate, it is characterized by native support for microservices architecture.
The Kubernetes project is derived from Borg, which can be said to be the essence of Borg's design ideas, and absorbs the experience and lessons of the Borg system.
<h1>summary:</h1>
As a container cluster management tool, Kubernetes provides unique insights and new ideas for container cluster management while advanced engines such as Docker have driven the rise and popularity of container technology, from Borg's Cell cluster management to Kubernetes' multi-copy Pods, from Borg's Cell cluster management.
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