A2.2.2 · Network architecture
A2.2.2 · 网络架构
Server Types
服务器类型
Checking one email silently involves a domain name server translating an address, a mail server storing the message, and often a web server rendering the inbox itself, three completely different jobs, done by three completely different pieces of software.
查收一封邮件的背后,悄悄涉及域名服务器解析地址、邮件服务器存储邮件,往往还有 Web 服务器渲染收件箱本身,这是三项完全不同的工作,由三种完全不同的软件完成。
Explainer
讲解
A server is a computer or piece of software that provides a specific service to other computers (clients) on a network, on request.
服务器是一台计算机或一段软件,按请求向网络上的其他计算机(客户端)提供特定的服务。
A single physical machine very often runs several of these server applications at once, each one is really a piece of software listening for its own kind of request, not necessarily a separate box of hardware.
同一台物理机器往往会同时运行好几个这样的服务器应用程序,每一个其实都是一段监听自己特定类型请求的软件,而不一定是一台独立的硬件设备。
Worked example
示例讲解
Six kinds of server
六种服务器
The statement names four factors to consider for each one: function, scalability, reliability and security. Click each server to see all four.
该考纲陈述为每一种服务器列出了四项需要考虑的因素:功能、可扩展性、可靠性和安全性。点击每个服务器即可查看全部四项。
Worked example
示例讲解
Tracing a DNS lookup
追踪一次 DNS 查询
Mia types www.riverbendschool-example.org into her browser. Neither her device nor her school's own network has ever looked this address up before.
Mia 在浏览器中输入了 www.riverbendschool-example.org。她的设备和她学校自己的网络此前都从未查询过这个地址。
Ask the configured DNS server. Mia's device sends the request to whichever DNS server it was told to use, either set manually or handed to it earlier by DHCP.
询问已配置的 DNS 服务器。Mia 的设备将请求发送给它被告知要使用的 DNS 服务器,该服务器要么是手动设置的,要么是此前由 DHCP 分配给它的。
Not found locally, escalate. The school's DNS server has never cached this address either, so it forwards the same question up the chain to a server that's more likely to know, and that continues until one does.
本地未找到,向上转发。学校的 DNS 服务器同样也没有缓存过这个地址,于是它将同样的问题沿链条向上转发给更有可能知道答案的服务器,这一过程会持续,直到有服务器知道答案为止。
Answer returned and cached. The address is found, sent back down the same chain to Mia's device, and cached along the way, so the exact same question asked again soon after gets answered instantly, with no need to repeat the whole chain.
答案返回并被缓存。地址被找到后,沿同一条链条返回给 Mia 的设备,并在途中被缓存下来,因此不久后再次提出完全相同的问题时就能立即得到答案,无需重复整条链条的查询过程。
Check your understanding
检验你的理解
A busy online shop wants incoming customer requests spread across five identical web servers, and wants to cache the shop's most commonly viewed product pages so those five servers don't have to regenerate them for every single visitor. Which type of server is built specifically for this?
一家繁忙的网店希望将传入的客户请求分散到五台完全相同的 Web 服务器上,并希望缓存店内最常被浏览的商品页面,这样这五台服务器就不必为每一位访客都重新生成这些页面。哪种服务器类型正是为此而设计的?
Common mistake
常见错误
RecurringA common weak answer treats "proxy server" as a single idea, without distinguishing which side it's actually acting on behalf of. A proxy server acts on behalf of the CLIENT (browsing the internet for a device, so the device's own address stays hidden). A reverse proxy acts on behalf of the SERVER (distributing incoming requests across several backend servers, and caching responses for them).
反复出现常见的薄弱答案会把"代理服务器"当作单一的概念,没有区分它究竟代表哪一方行事。代理服务器代表客户端行事(替设备浏览互联网,从而让设备自身的地址保持隐藏)。反向代理则代表服务器行事(将传入的请求分散到多台后端服务器上,并为它们缓存响应)。
Treated as one idea: "A proxy server helps manage internet traffic for a network." True of both a proxy and a reverse proxy, but doesn't say which side each one actually serves, which is the entire distinction being asked about.
被当作单一概念: "代理服务器有助于管理网络的互联网流量。" 这句话对代理和反向代理都成立,但并未说明各自实际服务于哪一方,而这正是题目所要考察的全部区别所在。
Names the actual distinction: "A proxy server sits in front of client devices, making requests to the internet on their behalf so the client's own address stays hidden. A reverse proxy sits in front of a group of servers instead, spreading incoming requests across them and caching common responses, so the servers behind it stay hidden from the client." States exactly whose behalf each one acts on, which is what actually earns the marks.
说明了真正的区别: "代理服务器位于客户端设备之前,代表它们向互联网发出请求,从而让客户端自身的地址保持隐藏。反向代理则位于一组服务器之前,将传入的请求分散到这些服务器上并缓存常见的响应,从而让其背后的服务器对客户端保持隐藏。" 准确说明了各自代表哪一方行事,而这正是真正得分的关键。
Revision questions
复习题
Past-paper style. Write an answer, then reveal the marking points and mark yourself.
采用历年真题风格。写下答案,然后展开评分要点给自己打分。
[2]Describe the function of a domain name server.
[2]描述域名服务器的功能。
Marking points
评分要点
- A domain name server turns a typed domain name into the IP address of the server that hosts it.
- This lets the browser actually connect, since the network routes by IP address, not by name. Answers are cached so a repeated lookup is instant.
- 域名服务器把键入的域名转换成托管它的服务器的 IP 地址。
- 这让浏览器能真正连接,因为网络按 IP 地址路由,不按名称。答案被缓存,所以重复的查找是即时的。
[3]Explain how RAID contributes to a file server's reliability.
[3]解释 RAID 如何提升文件服务器的可靠性。
Marking points
评分要点
- RAID stores the same data across several disks, using mirroring (a full copy on another disk) or parity (extra information that can rebuild a missing disk).
- So if one disk in the server fails, the data is still available from the other disks and the file server keeps running without data loss.
- RAID 把同样的数据分布在多块磁盘上,使用镜像(在另一块磁盘上放完整副本)或校验(能重建缺失磁盘的额外信息)。
- 所以如果服务器里一块磁盘故障,数据仍可从其他磁盘获得,文件服务器继续运行,不丢数据。
[4]Distinguish between the roles of a proxy server and a reverse proxy server.
[4]区分代理服务器与反向代理服务器的作用。
Marking points
评分要点
- A proxy server acts on behalf of the client: it makes requests to the internet for a device, so the client's own IP address stays hidden, and it can cache pages and filter requests.
- A reverse proxy server acts on behalf of a group of servers: it sits in front of them, receives all incoming requests and distributes them, hiding the real servers and spreading the load.
- The difference is which side each one serves and hides.
- 代理服务器代表客户端行事:它替设备向互联网发出请求,使客户端自己的 IP 地址被隐藏,还能缓存页面、过滤请求。
- 反向代理服务器代表一组服务器行事:它位于它们前面,接收所有进入的请求并分发,隐藏真实服务器并分摊负载。
- 区别在于每一个服务和隐藏的是哪一边。
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
Free account: unlock every revision question and flashcard for A2.2.2, and every other IB CS 2027 statement.
免费账户:解锁 A2.2.2 以及所有其他 IB CS 2027 考纲陈述的全部复习题和记忆卡片。