Servicenow 简明教程
ServiceNow - Cloud Services
提供云计算的供应商称为云服务。“云”在云计算中是指互联网。因此， cloud computing refers to providing computing services like storage, CPU, networking, RAM, servers, etc. over the Internet 。但是，云计算多年来不断发展，因此提供了一系列服务，如软件开发平台、工具、增强型基础设施管理等。
The vendors providing Cloud computing are called Cloud services. The “cloud” in cloud computing refers to the internet. Therefore, cloud computing refers to providing computing services like storage, CPU, networking, RAM, servers, etc. over the Internet. However, cloud computing has evolved over the years and thereby, providing a range of services like software development platforms, tools, enhanced infrastructure management, etc.
市场上的主要云服务提供商包括谷歌、亚马逊、IBM、甲骨文、SAP 等。一个云计算的完美示例是 Google 文档。所有文档都存储在 Google 云中，可以从任何地方、任何时间和任何设备访问文档，无需在系统中安装任何特定软件（文档查看器/编辑器）。可通过用于访问文档的文档和应用程序在云中使用。
The major cloud service providers in the market include Google, Amazon, IBM, Oracle, SAP, etc. A perfect example of cloud computing is Google docs. All your documents are stored in Google cloud and you can access your documents from anywhere, anytime and from any device without having any specific software (Document viewer/editor) installed in your system. Your documents and application through which you can access your documents, both are available in the cloud.
下图给出了云计算的总体视图。
The below figure gives an overall view of cloud computing.
可以基于组织或个人的要求和业务需求以多种方式实施云计算。云基础架构可以以多种方式设置，称为云部署模型。
Cloud computing can be implemented in a number of ways based on the organisation’s or individual’s requirement and business needs. Cloud infrastructure can be setup in a number of ways, which are referred to as cloud deployment models.
Types of deployment models
部署模型的类型如下−
The types of deployment models are as follows −
Public cloud
此类云可免费供公众使用。它可以归属于提供免费服务的大公司或政府组织。例如 - Gmail、Dropbox、Microsoft Azure 等。
This type of cloud is freely available for public use. It can be owned by big companies or government organisations providing free of cost services. For Example - Gmail, Dropbox, Microsoft Azure, etc.
Private cloud
私有云由单个组织专属用于其内部目的。一般来说，与防火墙相伴，限制了公众使用云。例如，一个大型跨国公司运营私有云，以便其多个子公司或业务部门用于其内部计算/共享资源。
Private cloud is used exclusively by a single organisation for their internal purposes. They are generally, accompanied by firewalls restricting the general public from using the cloud. For example, a big MNC operating private cloud for its multiple subsidiaries or business unit for their internal computing/sharing resources.
Community cloud
它是公有云和私有云之间的模型。只有选定的组织或拥有相同业务领域或相同议程的用户社区才能访问此类云。例如，所有银行都维护着一个公共云，其中包含贷款违约者的数据库，在发放新贷款时在银行之间共享以供参考。
It is a model between public and private cloud. Only selected organisations or communities of users having the same line of business or same agenda have access to this type of cloud. For example, all the banks maintaining a common cloud having the database of loan defaulters, which is shared among the banks to refer while issuing a fresh loan.
Hybrid cloud
此类云基础架构是上面讨论的任何部署模型（公有、私有和社区）的混合体。例如，一家大公司维护了一个由公有和私有组成的混合云。公司的所有敏感信息，如未来战略、内部政策等，都存储和处理在私有云中，而产品详情、价格、订单等公开信息则处理和存储在公有云中。
This type of cloud infrastructure is a mixture of any of the deployment models discussed above (Public, Private and Community). For example, a large company maintaining a hybrid cloud of public and private. All the sensitive information of the companies like future strategies, internal policies, etc. are stored and processed in private cloud while public information such as product details, prices, orders are processed and stored in a public cloud.
Cloud Service Models
还有云服务模型，其分类基于云服务提供商提供的服务。我们在下面讨论了云的三种服务模型−
There are also cloud service models, which are categorised based on the services offered by the cloud service providers. We have discussed the three service models of cloud below −
Infrastructure as a service (IaaS)
这是云服务最基本的层面，在该层面中，客户只从云服务提供商处获取计算资源或虚拟硬件，如存储、CPU、RAM 等。客户完全负责管理云中的应用程序、操作系统、软件、数据库等。例如 - Rackspace、Digital ocean 等。
This is the most fundamental level of cloud service, where in customer only takes computing resources or virtual hardware like storage, CPU, RAM, etc. from the cloud service providers. The customer takes complete ownership of managing applications, operating systems, software, databases, etc. in the cloud. For example − Rackspace, Digital ocean, etc.
Platform as a service (PaaS)
这是 IaaS 的进一步一级。在这里，除计算资源/虚拟硬件外，云服务提供商还提供操作系统、一些软件服务和工具。客户负责使用这些软件服务/工具开发应用程序并进行维护。例如 - Google App Engine、Apache Stratos、ServiceNow 等。
This is one level further to IaaS. Here, along with the computing resources/virtual hardware, operating system, some software service and tools are also provided by the cloud service providers. The customer takes ownership of developing application using those software services/tools and maintaining it. For example − Google App Engine, Apache Stratos, ServiceNow, etc.
Software as a service (SaaS)
此服务模型通过互联网提供功能齐全、可随时使用的软件。服务提供商完全负责管理软件、服务器、数据库、基础架构等。SaaS 服务可能是免费的，也可以按月/年付费使用。例如：Salesforce、Google Apps、ServiceNow 等。
This service model offers fully functional, ready to use software over the internet. The service provider takes the complete ownership of managing the software, servers, database, infrastructure, etc. The SaaS services can be free or available at monthly/yearly prices. For example: Salesforce, Google Apps, ServiceNow, etc.
我们可以根据下图总结基于云的部署模型和服务模型。
We can summarise the deployment model and service model of the cloud based on the below figure.
ServiceNow 是一个高度灵活的应用程序，提供 PaaS 和 SaaS 选项。其 SaaS 产品提供全功能工作流自动化和 ITSM 工具，而其 PaaS 产品允许用户根据业务要求在现有套件之上开发自定义应用程序。我们将在后面的章节中详细研究这一点。
ServiceNow is a highly flexible application which provides the option of PaaS as well as SaaS. Its SaaS offering provides fully functional workflow automation and ITSM tools, while its PaaS offering, allows the user to develop a custom application on the top of existing suite, as per the business requirement. We will study more about this in later sections.