A1.1.9 · Computer fundamentals
A1.1.9 · 计算机基础
Types of Service in Cloud Computing
云计算中的服务类型
Instead of buying and running its own servers, an organisation can rent computing from a provider over the internet. How much of the stack the provider looks after, and how much the customer keeps control of, is what separates the three service models.
一个组织不必自己购买和运行服务器,而是可以通过互联网向服务商租用计算资源。服务商负责多少层、客户自己掌控多少层,正是区分这三种服务模型的关键。
A1's guiding question covers how software interacts with the system it runs on. Cloud service models are a modern answer: the same application can sit on hardware you own, a platform you rent, or infrastructure you configure.
A1 的引导性问题涉及软件如何与它所运行的系统交互。云服务模型是一种现代的回答:同一个应用可以运行在你自有的硬件上、你租用的平台上,或你自己配置的基础设施上。
Explainer
讲解
What cloud computing is
云计算是什么
Cloud computing is using computing resources (applications, platforms or hardware) that are hosted by a provider and reached over the internet, paid for as they are used rather than owned outright. The three service models differ in where the line falls between what the provider manages and what the customer manages.
云计算是使用由服务商托管、通过互联网访问的计算资源(应用、平台或硬件),按使用量付费,而不是彻底买断。三种服务模型的区别在于服务商管理的部分与客户管理的部分之间那条界线画在哪里。
Explainer
讲解
SaaS, PaaS and IaaS
SaaS、PaaS 和 IaaS
| Model | What you get | What the provider handles | What you handle |
|---|---|---|---|
| Software as a service (SaaS) | A finished application, used through a web browser or app | Everything: the servers, the platform, the application code, updates and backups | Only your own data and account settings |
| Platform as a service (PaaS) | A ready-made environment to build, test and deploy your own software | The servers, operating system, runtimes and build tools | Your application code and its data |
| Infrastructure as a service (IaaS) | Virtual servers, storage and networking that you configure yourself | The physical hardware and the virtualisation layer | The operating system upwards: patching, runtimes, application, data |
| 模型 | 你得到什么 | 服务商负责什么 | 你负责什么 |
|---|---|---|---|
| 软件即服务(SaaS) | 一个成品应用,通过网页浏览器或 App 使用 | 一切:服务器、平台、应用代码、更新和备份 | 只有你自己的数据和账户设置 |
| 平台即服务(PaaS) | 一个现成的环境,用来构建、测试和部署你自己的软件 | 服务器、操作系统、运行时和构建工具 | 你的应用代码及其数据 |
| 基础设施即服务(IaaS) | 虚拟服务器、存储和网络,由你自己配置 | 物理硬件和虚拟化层 | 从操作系统往上:打补丁、运行时、应用、数据 |
Going from SaaS to PaaS to IaaS, the customer gains control and flexibility (choice of operating system, installed software, configuration) but takes on more work (patching, scaling, securing what they now manage) and needs more technical knowledge. Neither end is "better", they suit different needs.
从 SaaS 到 PaaS 再到 IaaS,客户获得更多的控制权和灵活性(可选操作系统、可安装软件、可自行配置),但也承担更多工作(打补丁、扩容、保护自己现在管理的部分),并且需要更多技术知识。两端没有谁"更好",它们适合不同的需求。
Explore
探索
The control ladder
控制权阶梯
The same seven layers make up any running application. Each model just draws the provider-manages / you-manage line in a different place. Click a model to see where its line falls.
任何一个运行中的应用都由同样的七层组成。每种模型只是把"服务商管理 / 你管理"这条线画在不同的位置。点击一个模型,看看它的线画在哪里。
Worked example
例题
Picking a model per scenario
按场景选择模型
| Scenario | Best fit | Why |
|---|---|---|
| A primary school wants email and shared documents for staff, with no IT team | SaaS | They need working software, not a platform to build on. The provider handles updates, backups and security, which suits an organisation with no technical staff |
| A small studio is building a booking web app and wants to ship it without configuring servers | PaaS | The developers write and deploy their code; the provider supplies the runtime, database and scaling. Their effort goes into the app, not the infrastructure |
| A research group needs to run custom simulation software on a specific Linux version with GPUs, only during term | IaaS | They need to choose the operating system and installed libraries themselves, and to switch the servers off between projects to control cost. That level of control needs raw infrastructure |
| 场景 | 最合适 | 原因 |
|---|---|---|
| 一所小学想为教职工提供电子邮件和共享文档,而且没有 IT 团队 | SaaS | 他们需要能用的软件,而不是一个用来搭建的平台。服务商负责更新、备份和安全,这适合没有技术人员的组织 |
| 一个小工作室在开发一个预订网页应用,想在不配置服务器的情况下把它上线 | PaaS | 开发者编写并部署自己的代码;服务商提供运行时、数据库和扩容。他们的精力放在应用上,而不是基础设施上 |
| 一个研究小组需要在特定 Linux 版本、带 GPU 的环境上运行自定义仿真软件,而且只在学期内使用 | IaaS | 他们需要自己选择操作系统和安装的库,并在项目之间关掉服务器以控制成本。这种程度的控制需要原始的基础设施 |
Check your understanding
检验你的理解
A development team wants to deploy a web application they wrote, without managing operating systems, runtimes or server scaling. Which model fits?
一个开发团队想部署他们自己写的网页应用,而不想管理操作系统、运行时或服务器扩容。哪种模型合适?
Common mistake
常见错误
RecurringAnswers often rank the models, calling IaaS "the most powerful" or SaaS "the most basic". The models are not a quality scale. More control also means more responsibility: with IaaS the customer must patch the operating system, size the servers and secure everything above the hardware. For an organisation with no technical staff, SaaS is the better choice, not the weaker one. Always tie the choice to the scenario: who will manage it, how much they need to configure, how cost should scale.
反复出现答案常常给这些模型排名,说 IaaS"最强大"或 SaaS"最基础"。这些模型不是一个质量等级。更多的控制也意味着更多的责任:用 IaaS 时,客户必须给操作系统打补丁、规划服务器规模,并保护硬件之上的一切。对于没有技术人员的组织,SaaS 是更好的选择,而不是更弱的选择。始终把选择与场景挂钩:谁来管理、需要配置多少、成本应如何随规模变化。
Ranks the models: "IaaS is the best because you get the most control; SaaS is only for people who cannot set up their own servers."
给模型排名: "IaaS 最好,因为你得到最多的控制;SaaS 只适合那些搭不起自己服务器的人。"
Right: "IaaS gives the most control and flexibility but the customer must manage the operating system upwards, so it needs technical staff. SaaS gives the least control but the provider manages everything, which suits an organisation that just needs working software. The right model depends on how much the customer needs to configure and who will maintain it."
正确: "IaaS 给予最多的控制权和灵活性,但客户必须管理从操作系统往上的部分,因此需要技术人员。SaaS 给予最少的控制权,但服务商管理一切,这适合只需要能用的软件的组织。正确的模型取决于客户需要配置多少,以及由谁来维护。"
Revision questions
复习题
Specimen-paper style. Write an answer, then reveal the marking points and mark yourself.
采用样卷风格。写下答案,然后展开评分要点给自己打分。
[2]Identify the service model in which the provider manages everything except the customer's data, and give one example use.
[2]指出在哪种服务模型中服务商管理除客户数据以外的一切,并举一个使用例子。
Marking points
评分要点
- The model is Software as a Service (SaaS).
- One example use (any one): staff email; an online office suite or shared documents; a customer-relationship or accounting application used through a browser.
- 这个模型是软件即服务(SaaS)。
- 一个使用例子(任选其一):员工电子邮件;在线办公套件或共享文档;通过浏览器使用的客户关系或会计应用。
[3]A software team picks PaaS to develop their new application. Give three reasons this model fits what they need.
[3]一个软件团队选择 PaaS 来开发他们的新应用。给出三条这个模型符合他们需求的理由。
Marking points
评分要点
- Any three: the provider supplies the servers, operating system, runtime and build tools, so the team does not configure infrastructure; it scales the application automatically as demand grows; the team's effort goes into writing and deploying their own code; updates and security of the platform are handled by the provider; they can deploy quickly.
- 任选三点:服务商提供服务器、操作系统、运行时和构建工具,团队不必配置基础设施;随着需求增长,它自动为应用扩容;团队的精力放在编写和部署自己的代码上;平台的更新和安全由服务商负责;他们可以快速部署。
[4]Compare the degree of control and the maintenance responsibility that a customer has under IaaS versus SaaS.
[4]比较客户在 IaaS 与 SaaS 下所拥有的控制程度和维护责任。
Marking points
评分要点
- Control: under IaaS the customer chooses the operating system and installed software and configures the virtual servers; under SaaS the customer controls only their own data and account settings.
- Maintenance: under IaaS the customer must patch the operating system, keep runtimes updated and secure everything above the virtualisation layer; under SaaS the provider does all of that.
- 控制权:在 IaaS 下,客户选择操作系统和已安装软件,并配置虚拟服务器;在 SaaS 下,客户只控制自己的数据和账户设置。
- 维护:在 IaaS 下,客户必须为操作系统打补丁、保持运行时更新,并保障虚拟化层以上一切的安全;在 SaaS 下,这些全由服务商完成。
[4]A company runs simulation software that needs a specific operating system and is only used a few weeks a year. Recommend a cloud service model and justify the choice.
[4]一家公司运行的仿真软件需要特定的操作系统,而且每年只用几周。推荐一种云服务模型并说明理由。
Marking points
评分要点
- Recommend Infrastructure as a Service (IaaS).
- The software needs a specific operating system, so the customer must be able to choose and configure the OS themselves, which IaaS allows.
- It is used only a few weeks a year, so the customer can switch the virtual servers off the rest of the time and only pay for what is used, controlling cost.
- SaaS or PaaS would not give the control over the operating system that the software requires.
- 推荐基础设施即服务(IaaS)。
- 该软件需要特定的操作系统,所以客户必须能自己选择和配置操作系统,而 IaaS 允许这样做。
- 它一年只用几周,所以客户在其余时间可以关掉虚拟服务器,只为用到的部分付费,从而控制成本。
- SaaS 或 PaaS 不能提供该软件所需的对操作系统的控制。
[3]Explain how moving from SaaS to IaaS changes the way computing resources scale with demand and cost.
[3]解释从 SaaS 转向 IaaS 会如何改变计算资源随需求和成本变化的方式。
Marking points
评分要点
- Under SaaS the provider owns and scales the resources, adding capacity automatically as demand rises and charging a fixed or per-user fee.
- Under IaaS the customer rents virtual servers and must arrange scaling themselves (starting more servers, or setting up auto-scaling), and pays for the resources actually running.
- So the customer gains fine control of how resources match demand and cost, but takes on the work of managing it.
- 在 SaaS 下,服务商拥有并扩展资源,随需求上升自动增加容量,并按固定费用或按用户收费。
- 在 IaaS 下,客户租用虚拟服务器,必须自己安排扩容(启动更多服务器,或设置自动扩容),并为实际运行的资源付费。
- 所以客户获得对“资源如何匹配需求与成本”的精细控制,但也承担了管理它的工作。
Flashcards
记忆卡片
Active recall for this statement’s key terms.
针对本条考纲陈述关键术语的主动回忆练习。
Keep this statement’s practice with you
把这条考纲陈述的练习保存下来
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免费账户:解锁 A1.1.9 以及所有其他 IB CS 2027 考纲陈述的全部复习题和记忆卡片。