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204 lines
15 KiB
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204 lines
15 KiB
Markdown
Kubernetes是什么？What is Kubernetes?
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============================================================
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本文是Kubernetes的概览。
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* [为什么选择Kubernetes?][7]
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* [为什么我需要Kubernetes，它能做什么?][1]
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* [Kubernetes是一个什么样的平台?][2]
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* [Kubernetes不是什么？][3]
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* [Kubernetes这个单词的含义？k8s?][4]
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* [接下来][8]
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Kubernetes 是一款跨集群的 [专门为自动化部署、缩放、操作应用程序容器的开源平台][25] , 提供了以容器为中心的基础架构。
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使用Kubernetes, 你可以快速、高效地满足用户以下的需求：
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* 快速精准地部署应用程序
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* 即时缩放应用程序
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* 无缝展现新特征
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我们的目标是，在公有或私有云中，培育出可以释放正在运行的程序的负担的一系列工具和组件的生态系统。
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#### Kubernetes 的优势
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* **轻便**: 公有云、私有云、混合云、多态云
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* **可扩展**: 模块化、组件化，可添加插件、可Hook
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* **自动修正**: 自动布局、自动重启、自动复制、自动缩放
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Google公司于2014年启动了Kubernetes项目。Kubernetes是在[Google的长达15年的成规模的产品运行工作量的经验下][26]构建的, 结合了公司中最优秀的创意，并在社区中经历了反复地实践。
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### 为什么选择容器?
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想要知道你为什么要选择使用 [容器][27]?
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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.
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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.
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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.
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程序部署的 _旧方法_ 是指，通过操作系统包管理器在主机上安装程序。这样做的坏处是，容易混淆程序之间以及程序和主机系统之间的可执行文件、配置文件、库、生命周期。为了达到精准展现和精准回撤，你可以搭建一台不可变的虚拟机映象。但是虚拟机体量往往过于庞大。
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容器部署的 _新方法_ 是基于操作系统级别的可视化，而非硬件可视化。容器彼此是孤立的，相对于主机也是独立的：它们有自己的文件系统，彼此之间不能看到对方的进程，分配到的计算资源都是有边界的。它们比虚拟机更容易搭建。并且由于和基础架构、主机文件系统是解耦的，它们可以在不同类型的云上或分布式OS上应用。
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正因为容器又小又快，每一个容器映象都可以打包装载一个程序。这种一对一的「程序 - 映象」联系带给了容器诸多便捷。有了容器，静态容器映象可以在编译/发布时期创建，而非部署时期。因此，每个应用不必再等待和整个应用栈其它部分进行整合，也不必和产品基础架构环境之间进行妥协。在编译/发布时期生成容器映象建立了一个持续地把开发转化为产品的环境。相似地，容器远比虚拟机更加透明，尤其在设备监控和管理上。这一点，在容器的进程生命周期被基础架构管理而非被容器内的进程监督器隐藏掉时，尤为显著。最终，随着每个容器内都装载了单一的程序，管理容器就等于管理或部署整个应用。
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Summary of container benefits:
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* **Agile application creation and deployment**: Increased ease and efficiency of container image creation compared to VM image use.
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* **Continuous development, integration, and deployment**: Provides for reliable and frequent container image build and deployment with quick and easy rollbacks (due to image immutability).
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* **Dev and Ops separation of concerns**: Create application container images at build/release time rather than deployment time, thereby decoupling applications from infrastructure.
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* **Environmental consistency across development, testing, and production**: Runs the same on a laptop as it does in the cloud.
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* **Cloud and OS distribution portability**: Runs on Ubuntu, RHEL, CoreOS, on-prem, Google Container Engine, and anywhere else.
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* **Application-centric management**: Raises the level of abstraction from running an OS on virtual hardware to run an application on an OS using logical resources.
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* **Loosely coupled, distributed, elastic, liberated [micro-services][5]**: Applications are broken into smaller, independent pieces and can be deployed and managed dynamically – not a fat monolithic stack running on one big single-purpose machine.
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* **Resource isolation**: Predictable application performance.
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* **Resource utilization**: High efficiency and density.
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#### Why do I need Kubernetes and what can it do?
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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.
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Kubernetes satisfies a number of common needs of applications running in production, such as:
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* [Co-locating helper processes][9], facilitating composite applications and preserving the one-application-per-container model
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* [Mounting storage systems][10]
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* [Distributing secrets][11]
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* [Checking application health][12]
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* [Replicating application instances][13]
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* [Using Horizontal Pod Autoscaling][14]
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* [Naming and discovering][15]
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* [Balancing loads][16]
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* [Rolling updates][17]
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* [Monitoring resources][18]
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* [Accessing and ingesting logs][19]
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* [Debugging applications][20]
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* [Providing authentication and authorization][21]
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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.
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#### How is Kubernetes a platform?
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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.
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[Labels][28] empower users to organize their resources however they please. [Annotations][29]enable users to decorate resources with custom information to facilitate their workflows and provide an easy way for management tools to checkpoint state.
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Additionally, the [Kubernetes control plane][30] is built upon the same [APIs][31] that are available to developers and users. Users can write their own controllers, such as [schedulers][32], with [their own APIs][33] that can be targeted by a general-purpose [command-line tool][34].
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This [design][35] has enabled a number of other systems to build atop Kubernetes.
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#### What Kubernetes is not
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Kubernetes is not a traditional, all-inclusive PaaS (Platform as a Service) system. It preserves user choice where it is important.
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Kubernetes:
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* Does not limit the types of applications supported. It does not dictate application frameworks (e.g., [Wildfly][22]), restrict the set of supported language runtimes (for example, Java, Python, Ruby), cater to only [12-factor applications][23], nor distinguish _apps_ from _services_ . 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.
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* Does not provide middleware (e.g., message buses), data-processing frameworks (for example, Spark), databases (e.g., mysql), nor cluster storage systems (e.g., Ceph) as built-in services. Such applications run on Kubernetes.
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* Does not have a click-to-deploy service marketplace.
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* Does not deploy source code and does not build your application. Continuous Integration (CI) workflow is an area where different users and projects have their own requirements and preferences, so it supports layering CI workflows on Kubernetes but doesn’t dictate how layering should work.
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* Allows users to choose their logging, monitoring, and alerting systems. (It provides some integrations as proof of concept.)
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* Does not provide nor mandate a comprehensive application configuration language/system (for example, [jsonnet][24]).
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* Does not provide nor adopt any comprehensive machine configuration, maintenance, management, or self-healing systems.
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On the other hand, a number of PaaS systems run _on_ Kubernetes, such as [Openshift][36], [Deis][37], and [Eldarion][38]. 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.
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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.
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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.
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#### What does _Kubernetes_ mean? K8s?
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The name **Kubernetes** originates from Greek, meaning _helmsman_ or _pilot_ , and is the root of _governor_ and [cybernetic][39]. _K8s_ is an abbreviation derived by replacing the 8 letters “ubernete” with “8”.
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--------------------------------------------------------------------------------
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via: https://kubernetes.io/docs/concepts/overview/what-is-kubernetes/
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作者：[kubernetes.io][a]
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译者：[译者ID](https://github.com/译者ID)
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校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
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[a]:https://kubernetes.io/
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[1]:https://kubernetes.io/docs/concepts/overview/what-is-kubernetes/#why-do-i-need-kubernetes-and-what-can-it-do
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[2]:https://kubernetes.io/docs/concepts/overview/what-is-kubernetes/#how-is-kubernetes-a-platform
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[3]:https://kubernetes.io/docs/concepts/overview/what-is-kubernetes/#what-kubernetes-is-not
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[4]:https://kubernetes.io/docs/concepts/overview/what-is-kubernetes/#what-does-kubernetes-mean-k8s
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[5]:https://martinfowler.com/articles/microservices.html
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[6]:https://kubernetes.io/docs/concepts/overview/what-is-kubernetes/#kubernetes-is
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[7]:https://kubernetes.io/docs/concepts/overview/what-is-kubernetes/#why-containers
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[8]:https://kubernetes.io/docs/concepts/overview/what-is-kubernetes/#whats-next
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[9]:https://kubernetes.io/docs/concepts/workloads/pods/pod/
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[10]:https://kubernetes.io/docs/concepts/storage/volumes/
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[11]:https://kubernetes.io/docs/concepts/configuration/secret/
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[12]:https://kubernetes.io/docs/tasks/configure-pod-container/configure-liveness-readiness-probes/
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[13]:https://kubernetes.io/docs/concepts/workloads/controllers/replicationcontroller/
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[14]:https://kubernetes.io/docs/tasks/run-application/horizontal-pod-autoscale/
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[15]:https://kubernetes.io/docs/concepts/services-networking/connect-applications-service/
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[16]:https://kubernetes.io/docs/concepts/services-networking/service/
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[17]:https://kubernetes.io/docs/tasks/run-application/rolling-update-replication-controller/
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[18]:https://kubernetes.io/docs/tasks/debug-application-cluster/resource-usage-monitoring/
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[19]:https://kubernetes.io/docs/concepts/cluster-administration/logging/
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[20]:https://kubernetes.io/docs/tasks/debug-application-cluster/debug-application-introspection/
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[21]:https://kubernetes.io/docs/admin/authorization/
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[22]:http://wildfly.org/
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[23]:https://12factor.net/
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[24]:https://github.com/google/jsonnet
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[25]:http://www.slideshare.net/BrianGrant11/wso2con-us-2015-kubernetes-a-platform-for-automating-deployment-scaling-and-operations
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[26]:https://research.google.com/pubs/pub43438.html
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[27]:https://aucouranton.com/2014/06/13/linux-containers-parallels-lxc-openvz-docker-and-more/
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[28]:https://kubernetes.io/docs/concepts/overview/working-with-objects/labels/
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[29]:https://kubernetes.io/docs/concepts/overview/working-with-objects/annotations/
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[30]:https://kubernetes.io/docs/concepts/overview/components/
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[31]:https://kubernetes.io/docs/reference/api-overview/
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[32]:https://git.k8s.io/community/contributors/devel/scheduler.md
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[33]:https://git.k8s.io/community/contributors/design-proposals/extending-api.md
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[34]:https://kubernetes.io/docs/user-guide/kubectl-overview/
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[35]:https://github.com/kubernetes/community/blob/master/contributors/design-proposals/principles.md
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[36]:https://www.openshift.org/
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[37]:http://deis.io/
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[38]:http://eldarion.cloud/
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[39]:http://www.etymonline.com/index.php?term=cybernetics
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