The web, DNS, and cloud services
The World Wide Web is one application running on the internet. It relies on DNS to find servers and HTTP to fetch pages, and increasingly on cloud data centres.
Internet versus web
The internet is the global network infrastructure. The World Wide Web, invented by Tim Berners-Lee at CERN in 1989, is a system of linked documents and applications accessed through browsers. Email, video streaming, and online games also use the internet without necessarily being part of the web.
URLs
A uniform resource locator (URL) names a resource. In https://www.example.com/news/today.html, 'https' is the protocol, 'www.example.com' is the host name, and '/news/today.html' is the path on that server. URLs can also include query parameters after a question mark.
DNS
Humans remember names; routers need IP addresses. The Domain Name System (DNS) translates names such as example.com into IP addresses. It is a distributed, hierarchical database: root servers point to top-level domain servers (such as .com), which point to the domain's own name servers. Results are cached to keep lookups fast.
HTTP and HTTPS
The Hypertext Transfer Protocol (HTTP) is how browsers request resources and servers respond. Common methods include GET (retrieve) and POST (submit data). Responses carry status codes: 200 means OK, 404 means not found, and 500 means a server error. HTTPS is HTTP secured with TLS encryption, protecting data from eavesdropping and tampering; most web traffic now uses HTTPS.
Web pages
Web pages are built with HTML for structure and content, CSS for presentation and layout, and JavaScript for interactivity. The browser downloads these files, builds a model of the page, and renders it. Modern web applications, such as online email and document editors, run substantial JavaScript and talk to servers in the background.
Clients and servers
In the client-server model, clients, such as browsers and apps, request services, and servers provide them. Large sites use many servers behind load balancers that spread requests. Content delivery networks (CDNs) keep copies of popular content on servers around the world, so users fetch it from somewhere nearby, cutting latency.
Cloud computing
Cloud computing rents computing resources over the internet on demand. Infrastructure as a service (IaaS) provides virtual machines and storage; platform as a service (PaaS) provides managed environments for running code; software as a service (SaaS) delivers complete applications, such as web email. Cloud lets organisations scale up quickly without buying hardware, but creates dependence on providers.
Worked example
Typing www.example.com into a browser: the browser checks its cache, then asks a DNS resolver, which may ask root, .com, and example.com name servers to get the IP address. The browser opens a TCP connection, sets up TLS, and sends GET / over HTTPS. The server returns 200 OK with HTML; the browser then requests the CSS, JavaScript, and images it references, often from a CDN, and renders the page.
Key takeaways
The web runs on the internet but is not the same thing. URLs name resources by protocol, host, and path. DNS translates names to IP addresses through a cached hierarchy. HTTP requests use methods like GET and POST and return status codes like 200 and 404; HTTPS adds TLS encryption. HTML, CSS, and JavaScript build pages. Clients request, servers respond; load balancers and CDNs scale delivery. Cloud computing rents IaaS, PaaS, and SaaS on demand.
Flashcard
Linked documents and apps over the internet
Check your understanding
What does DNS do?