Uptime
Definition
The arithmetic is worth memorising, because the marketing figures compress badly. Over a 30-day month, 99 percent allows about 7 hours 18 minutes of downtime, 99.9 percent allows 43 minutes 49 seconds, 99.95 percent allows 21 minutes 54 seconds, and 99.99 percent allows 4 minutes 23 seconds. Each extra nine costs roughly ten times more to deliver, which is why serious guarantees stop around four. What counts as down is set by the definition, not by feeling: a monitor usually treats a connection failure, a timeout, or a 5xx response as downtime, and a slow but successful response as uptime. Planned maintenance is very often excluded from the figure, which is a detail worth checking before comparing two providers.
Why It Matters
The number only means something alongside how it is measured and what happens when it is missed. A provider checking from one location every fifteen minutes will miss a six-minute outage entirely; a check every thirty seconds from several regions will not. Service level agreements usually pay out in account credit rather than compensation for damage, so 99.9 percent with a credit clause is not insurance — it is a promise about effort. The practical difference matters most at the moments you cannot control: an hour of downtime is an inconvenience on a Tuesday night and a disaster on the morning a campaign goes out. Static content has an advantage here, because there is no database or application process that can fall over, and copies of the files sit on many machines rather than one.
How It Works
Monitoring is straightforward: a service requests a known URL from several regions at a fixed interval, records the status code and response time, and counts a failure only after a second check confirms it, so a single dropped packet is not logged as an outage. Uptime is then successful checks divided by total checks over the window. Behind the site, availability comes from having no single point of failure — files replicated across an edge network, so one point of presence going offline routes traffic to the next rather than returning errors. DNS is the part people forget: an expired domain or a nameserver failure takes a site down just as completely as a dead server, and no amount of replication upstream helps. Publishing a status page on a different host from the site is the small detail that turns an outage into a manageable one.
Real-World Example
A charity keeps its annual report on 99helpers at trust-report-2026.99helpers.site ahead of a press announcement. The file is served from an edge network rather than one machine, so when a regional node goes offline during the launch week, requests are answered from the next location and nobody downloading the PDF notices. An external monitor checking every minute from four regions records 100 percent for the month.
Common Mistakes
- ✕Comparing 99.9 percent with 99.99 percent as near-equivalent — the gap is about 39 minutes a month, which is most of a launch
- ✕Reading an uptime figure without reading the measurement interval, since a fifteen-minute check hides most short outages
- ✕Forgetting that planned maintenance windows are usually carved out of the promised number before it is published
- ✕Hosting the status page on the same infrastructure as the site, so it disappears exactly when it is needed
Related Terms
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.
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.
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.
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.
Origin Server
The machine or service holding the authoritative copy of a site, which a cache asks whenever it does not already have what a visitor wanted. Origin is a position in a delivery chain, not a kind of software.
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