# _uptime.is_ SLA calculator _informal_ specification

The _uptime.is_ SLA calculator has been developed on an ad-hoc basis in
response to specific needs of its creator.

## Simple SLA calculator

In its most simple form, the calculator outputs downtime duration in hours,
minutes and seconds given a specified uptime percentage.

The SLA uptime percentage may be specified in the URL, or as a GET/POST form
parameter named `sla` (the form parameter having precedence):

* `https://uptime.is/<sla-percentage>`
* `https://uptime.is/?sla=<sla-percentage>`

The calculator outputs acceptable daily, weekly, monthly, quarterly and yearly
downtime durations given the provided SLA uptime percentage.

For convenience, special URLs are provided for _two--nine nines_, e.g.

* `https://uptime.is/two-nines`
* [...]
* `https://uptime.is/nine-nines`

## Complex SLA calculator

Simple SLA calculator described above assumes 24/7 uptime requirement (with
certain approximations further documented in <https://uptime.is/uptime.lsp>). In
real world, the requirements are often more relaxed, e.g. 8 hours on working
days. To accommodate for this scenario, the SLA calculator supports _complex_
mode, where it is possible to specify uptime requirement for each day of week.
The SLA uptime percentage is specified in a GET/POST form parameter named `sla`
and the durations in GET/POST form parameter called `dur` and repeated for each
day of week (i.e. 7 times and defaulting to 24, if not provided):

* `https://uptime.is/complex?sla=<sla-percentage>&dur=<monday-hours>&[...]&dur=<sunday-hours>`

The calculator outputs acceptable weekly, monthly, quarterly and yearly
downtime durations given the provided SLA uptime percentage.

## Reverse SLA calculator

Reverse SLA calculator performs the opposite operation, and converts downtime
duration into corresponding SLA uptime percentage. The downtime duration may be
provided as a number of seconds (e.g. `42`) or as a combination of hours,
minutes and/or seconds of downtime using the `h`, `m` or `s` unit (e.g. `13m
37s`). The reverse SLA calculator accepts the durations in the same way as the
complex SLA calculator.

The downtime duration is specified in a GET/POST form parameter named `down`
and the durations in GET/POST form parameter called `dur` and repeated for each
day of week (i.e. 7 times and defaulting to 24, if not provided):

* `https://uptime.is/reverse?down=<downtime-duration>&dur=<monday-hours>&[...]&dur=<sunday-hours>`

The calculator outputs SLA uptime percentage which would allow the specified
downtime with weekly, monthly, quarterly and yearly uptime calculations.