Domains, CDN & Web Delivery

Once a file is hosted, the rest is delivery: the name people type, the records that point that name somewhere, the certificate that makes the padlock appear, and the network of caches that decides whether the first byte arrives in 40 milliseconds or 400. This category covers the DNS side in detail — A records, CNAMEs, the reason a CNAME cannot sit at the apex of a domain, and why propagation is really just caches expiring on a TTL you set beforehand — alongside HTTPS, Cache-Control, ETags, compression, HTTP status codes and the performance measures that follow from all of it. It is the category to read when the domain is pointed but nothing loads.

35 terms in this category

A Record

An A record maps a name straight to an IPv4 address. It is the simplest record there is, and the only standard way to put a destination at the bare version of a domain.

Apex Domain

The apex domain is the bare name with nothing in front of it — acme.com rather than www.acme.com. It is also called the root domain, the naked domain or the zone apex.

Brotli Compression

Brotli is a lossless compression format for HTTP responses, published by Google in 2015 and supported by every current browser. On text it usually beats gzip by 15 to 20 percent, at the cost of more CPU time to compress.

Cache-Control

The HTTP response header that tells browsers and caches whether they may keep a copy of a file, for how long, and who is allowed to. It is the single biggest lever over how fast a site feels on a second visit.

Cache Hit Ratio

The share of requests answered from a cache rather than passed back to the origin, written as a percentage. It is the one number that tells you whether your caching setup is doing anything.

Cache Invalidation

Getting rid of cached copies of a file that is no longer correct, so visitors stop being served the old version. There are two ways to do it, and only one of them is reliable.

Canonical URL

A canonical URL is the one address you nominate as the real home of a piece of content when several addresses serve it. You declare it with a rel=canonical link in the page head, and search engines use it to decide which version to index.

CDN

A content delivery network: a set of servers spread across the world that keep copies of your files and answer each visitor from somewhere close to them. It is the service; the machines it runs on are its edge network.

CNAME Record

A CNAME record points one name at another name rather than at an address. Hosts ask for them because the addresses behind their target hostname can then change without you touching your zone.

Core Web Vitals

Core Web Vitals are the three page-experience measurements Google publishes and uses as a ranking signal: Largest Contentful Paint, Interaction to Next Paint and Cumulative Layout Shift. Each has a published threshold, and each is judged on real visits rather than a lab test.

Custom Domain

A custom domain is a name you own, pointed at content somebody else hosts, so visitors see files.acme.com instead of the provider's address. You keep the registration; the provider keeps the servers.

DNS

DNS, the Domain Name System, is the lookup service that turns a name like acme.com into an address a browser can actually connect to. Every page load begins with it.

DNS Propagation

DNS propagation is the wait after changing a record while cached copies of the old answer expire. Nothing spreads across the world; caches simply time out.

DNS Record

A DNS record is one entry in a domain's zone: a host, a type, a value and a TTL. The type decides what the value is allowed to mean.

DNS TTL

TTL is the number of seconds a DNS answer may be cached before it has to be fetched again. It is set per record, and it decides how long a mistake lasts.

Domain Name

A domain name is the readable address people type to reach something on the web, such as 99helpers.site. It stands in for a numeric server address that nobody would want to memorise.

Edge Network

The fleet of servers a delivery provider runs in cities around the world, positioned close to visitors rather than close to your origin. It is the machinery a CDN is built from.

ETag

A short identifier a server attaches to a file so a cache can later ask whether that exact version is still current. If it is, the answer comes back as a 304 with no body, and nothing is downloaded.

Gzip Compression

Gzip compression shrinks a response before it leaves the server and the browser expands it again on arrival. It is lossless, it has been supported by every browser for decades, and it typically cuts text files to a third of their original size.

HTTP/2

HTTP/2 is the second major version of the web's request protocol, standardised in 2015. It keeps the same URLs, methods, headers and status codes as HTTP/1.1, but changes how they travel: many requests share one connection instead of queueing behind each other.

HTTP Status Code

An HTTP status code is the three-digit number a server returns at the head of every response, saying what happened to the request. It is the first thing on the first line — a 200 means here is the file, a 404 means there is nothing at that address.

HTTPS

HTTP carried inside an encrypted TLS connection, shown in the browser as an https:// address. It is the same web protocol as before, with the traffic protected and the server's identity checked first.

HTTPS Redirect

A rule that answers any request arriving on plain HTTP with an instruction to fetch the same address over an encrypted connection instead. It makes the secure version the only one visitors actually see.

Largest Contentful Paint

Largest Contentful Paint, or LCP, marks the moment the biggest visible element in the viewport has finished rendering. It is the closest single number to the question a visitor actually asks: when did this page look like it had loaded?

Latency

Latency is the delay between sending something and it arriving — usually quoted as round-trip time, the milliseconds for a packet to reach a server and come back. It is a separate thing from bandwidth, which is how much data fits through per second once the first packet lands.

Mixed Content

A page loaded over an encrypted connection that pulls in at least one image, script, stylesheet or font over plain HTTP. The browser responds by removing the padlock, and for anything that can run code, by refusing to load it at all.

Nameserver

A nameserver is a machine that answers DNS questions. The set listed for your domain at the registry is the authoritative one — the only copy of your zone that anybody reads.

Point of Presence

A single physical location in a delivery network — the racks of servers in one city that answer requests from that region. Shortened to PoP, it is the smallest unit an edge network is counted in.

301 Redirect

A 301 redirect is a response telling the browser that a page has moved permanently and giving the new address. The old URL keeps working for anyone who follows the old link, but everything that matters now lives at the new one.

SSL Certificate

A small signed file that proves a server is genuinely the one answering for a given hostname, so a browser will open an encrypted connection to it. Everyone calls it an SSL certificate, though the protocol it is used with has been called TLS for years.