Glossary
Availability
The share of scheduled observations that received the expected response, per stated window.
Definition
Availability, as RELIASTRA measures it, is the number of observations in which the probe received the response its target expects (for public vendor records: HTTP 200 within 15 seconds), divided by all scheduled observations in a stated window, reported with the observation count and origins that produced it.
The problem
“99.99% uptime” without window, sample size and success definition is not a measurement - it is a decoration. The same month reads 100% from one origin and 99.2% from a region the observer did not run.
Why it matters
Four nines and three nines are 10x apart in downtime; a figure whose denominator is unstated cannot support an architecture decision, a contract clause, or a credit claim - it can only support a marketing bullet.
Practical example
On a RELIASTRA record, every window is printed as availability + observation count + latency quantiles, and a window with zero observations renders as “insufficient data” - never as 100%.
How RELIASTRA approaches it
Availability is derived at read time from stored observations only; nothing is backfilled or smoothed. The denominator is scheduled probes, so “we never ran the check” surfaces as freshness (staleness) rather than hiding inside the percentage.
Know what you depend on. Prove what it did.
RELIASTRA observes the external services your product relies on, attributes their failures, and produces evidence you can act on. Every new organization starts on a 14-day Pro trial.