SaaS: Software as a Service Cloud application services or “Software as a Service” (SaaS) are probably the most popular form of cloud computing and are easy to use. SaaS uses the Web to deliver applications that are managed by a third-party vendor and whose interface is accessed on the clients’ side. Most SaaS applications can be run directly from a Web browser, without any downloads or installations required. SaaS eliminates the need to install and run applications on individual computers. With SaaS, it’s easy for enterprises to streamline their maintenance and support, because everything can be managed by vendors: applications, runtime, data, middleware, O/S, virtualization, servers, storage, and networking. Gmail is one famous example of an SaaS mail provider.

PaaS: Platform as a Service The most complex of the three, cloud platform services or “Platform as a Service” (PaaS) deliver computational resources through a platform. What developers gain with PaaS is a framework they can build upon to develop or customize applications. PaaS makes the development, testing, and deployment of applications quick, simple, and cost-effective, eliminating the need to buy the underlying layers of hardware and software. One comparison between SaaS vs. PaaS has to do with what aspects must be managed by users, rather than providers: With PaaS, vendors still manage runtime, middleware, O/S, virtualization, servers, storage, and networking, but users manage applications and data.

IaaS: Infrastructure as a Service Cloud infrastructure services, known as “Infrastructure as a Service” (IaaS), deliver computer infrastructure (such as a platform virtualization environment), storage, and networking. Instead of having to purchase software, servers, or network equipment, users can buy these as a fully outsourced service that is usually billed according to the amount of resources consumed. Basically, in exchange for a rental fee, a third party allows you to install a virtual server on their IT infrastructure. Compared to SaaS and PaaS, IaaS users are responsible for managing more: applications, data, runtime, middleware, and O/S. Vendors still manage virtualization, servers, hard drives, storage, and networking. What users gain with IaaS is infrastructure on top of which they can install any required platforms. Users are responsible for updating these if new versions are released.

云服务模型主要分为三类:

软件即服务(SaaS) 平台即服务(PaaS) 基础设施即服务(IaaS)

软件即服务(SaaS)

SaaS是一种为最终客户集中托管和管理的软件。它通常基于多租户架构(应用程序的单个版本用于所有客户)，并且通常通过每月或每年的订阅获得许可。

例子 Office 365、Dropbox、Dynamics CRM Online都是SaaS软件的完美例子，订阅者每月或每年支付订阅费，就可以获得Exchange即服务(在线和/或桌面Outlook)或Storage即服务(OneDrive和Dropbox)。

平台即服务(PaaS)

使用PaaS，您可以将应用程序部署到云服务供应商提供的应用程序托管环境(专为构建、测试和部署软件应用程序而设计)中。开发人员有多种方式来部署他们的应用程序，而不需要知道任何支持它的后台发生了什么。

例子 Azure应用程序服务和Azure云服务(Web和工作人员角色)中的Web应用程序功能是PaaS的一个例子。

基础设施即服务(IaaS)

IaaS云供应商运行和管理运行虚拟化软件的服务器场，使您能够创建运行在供应商基础设施上的虚拟机(运行Windows或Linux)，并在其上安装您想要的任何东西。开发人员不能控制硬件或虚拟化软件，但他们可以控制几乎所有其他的东西。事实上，与PaaS不同的是，您完全要对它负责。

参考文献

书:云架构:云计算服务模型(SaaS、PaaS和IaaS)的设计决策

IaaS(基础设施即服务)

IaaS提供基础设施，如虚拟机和其他资源，如虚拟机磁盘映像库、基于块和文件的存储、防火墙、负载平衡器、IP地址、虚拟局域网等。基础设施即服务(IaaS)是云计算模型的基础层。

常见的例子:DigitalOcean、Linode、Rackspace、Amazon Web Services (AWS)、Cisco Metapod、Microsoft Azure、谷歌Compute Engine (GCE)是Iaas的一些流行例子。

平台即服务(PaaS)

PaaS或平台即服务模型为您提供计算平台，通常包括操作系统、编程语言执行环境、数据库和web服务器。从技术上讲，它是在IaaS之上的一个层，是继基础设施之后你需要的第二个东西，是一个平台。

常见的例子:AWS Elastic Beanstalk, Windows Azure, Heroku, Force.com，谷歌应用程序引擎，Apache Stratos。

软件即服务(SaaS)

在SaaS中，您可以访问安装在服务器上的应用程序服务。你不必担心软件的安装、维护或编码。您只需使用浏览器即可访问和操作该软件。你不需要下载或安装任何类型的安装或操作系统，软件只是供你访问和操作。软件维护或设置或帮助将由SaaS提供商公司提供，您只需支付使用费用。

常见的例子:谷歌应用程序，微软office365，谷歌文档，Gmail, WHMCS计费软件

IaaS, PaaS和SaaS之间的基本区别

有三种主要类型的云服务:IaaS、PaaS和SaaS。您可能在云提供商的网站上看到过这些缩写。在讨论细节之前，让我们先比较一下IaaS、PaaS和SaaS与传输的关系:

On-premises IT infrastructure is like owning a car. When you buy a car, you’re responsible for its maintenance, and upgrading means buying a new car. IaaS is like leasing a car. When you lease a car, you choose the car you want and drive it wherever you wish, but the car isn’t yours. Want an upgrade? Just lease a different car! PaaS is like taking a taxi. You don’t drive a taxi yourself, but simply tell the driver where you need to go and relax in the back seat. SaaS is like going by bus. Buses have assigned routes, and you share the ride with other passengers.

参考:https://rubygarage.org/blog/iaas-vs-paas-vs-saas

SaaS: Software as a Service Cloud application services or “Software as a Service” (SaaS) are probably the most popular form of cloud computing and are easy to use. SaaS uses the Web to deliver applications that are managed by a third-party vendor and whose interface is accessed on the clients’ side. Most SaaS applications can be run directly from a Web browser, without any downloads or installations required. SaaS eliminates the need to install and run applications on individual computers. With SaaS, it’s easy for enterprises to streamline their maintenance and support, because everything can be managed by vendors: applications, runtime, data, middleware, O/S, virtualization, servers, storage, and networking. Gmail is one famous example of an SaaS mail provider.

PaaS: Platform as a Service The most complex of the three, cloud platform services or “Platform as a Service” (PaaS) deliver computational resources through a platform. What developers gain with PaaS is a framework they can build upon to develop or customize applications. PaaS makes the development, testing, and deployment of applications quick, simple, and cost-effective, eliminating the need to buy the underlying layers of hardware and software. One comparison between SaaS vs. PaaS has to do with what aspects must be managed by users, rather than providers: With PaaS, vendors still manage runtime, middleware, O/S, virtualization, servers, storage, and networking, but users manage applications and data.

IaaS: Infrastructure as a Service Cloud infrastructure services, known as “Infrastructure as a Service” (IaaS), deliver computer infrastructure (such as a platform virtualization environment), storage, and networking. Instead of having to purchase software, servers, or network equipment, users can buy these as a fully outsourced service that is usually billed according to the amount of resources consumed. Basically, in exchange for a rental fee, a third party allows you to install a virtual server on their IT infrastructure. Compared to SaaS and PaaS, IaaS users are responsible for managing more: applications, data, runtime, middleware, and O/S. Vendors still manage virtualization, servers, hard drives, storage, and networking. What users gain with IaaS is infrastructure on top of which they can install any required platforms. Users are responsible for updating these if new versions are released.

我知道这个问题已经回答了一段时间，但这可能会有所帮助。

下面这些术语是什么意思? SaaS

软件即服务——从本质上讲，任何使用云中的内容运行的应用程序都被称为软件即服务，只要您不拥有它。

例如Gmail, Netflix, OneDrive等。

最终用户，每个人

IaaS

基础设施即服务意味着提供商允许其计算能力的一部分给其客户，它是由计算能力的效力购买的，并捆绑在虚拟机中。像谷歌云平台、AWS、阿里云这样的公司可以被称为IaaS提供商，因为他们以虚拟机的形式向用户出售处理能力(服务器、存储、网络)。

听众:IT专业人士，系统管理员

PaaS

平台即服务更像是IaaS和SaaS之间的中间人，客户不必处理服务器、网络和存储的细节，PaaS提供商可以随时提供一切。基本上，初始化开发环境是为了使构建应用程序更容易。

例如Heroku, AWS Elastic Beanstalk，谷歌App Engine等

听众:软件开发人员。

现在有各种各样的云服务，比如亚马逊的云服务 EC2和AWS, Apache Hadoop，微软Azure和许多其他。哪一个 每一个都属于什么类别，为什么?

Amazon EC2和AWS是一种基础设施即服务，因为您需要系统管理员来管理操作系统的工作流程。通常情况下，构建一个功能齐全的应用并不需要抽象。微软Azure也属于上述指导方针的范畴。

我真的没有使用过Apache Hadoop，所以我真的不能说。