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Cloud SLA Composite Availability Calculator

Work out cloud sla composite availability instantly with clear inputs, formula shown and shareable results.

About Cloud SLA Composite Availability Calculator

Composite availability multiplies across every service in the request path, so six dependencies at 99.95 percent give 99.7 percent — around 26 hours of expected downtime a year. Redundancy on individual services counteracts this by squaring their failure probability, which is why the number of non-redundant dependencies is the most important architectural availability decision.

Formula

Composite SLA

redundant service availability = 1 - (1 - SLA)^replicas; composite = SLA^(non-redundant services) x redundant availability^(redundant services)

Worked example

With the default values below, Cloud SLA Composite Availability Calculator returns Composite availability of 99.8001%. Change any input above and every figure here is recalculated in your browser.

Inputs used

Services in the request pathaccepts 1–50
6
SLA per serviceaccepts 90–100 %
99.95 %
Services deployed redundantlyaccepts 0–50
2
Independent replicas for those servicesaccepts 1–6
2

Results

Composite availability
99.8001%
Expected annual downtime
1,051 min
Availability with no redundancy
99.7004%
Availability of a redundant service
99.99998%

Step by step

  1. 1Values used
  2. 2Composite SLA
  3. 3Composite availability= 99.8001
  4. 4Expected annual downtime= 1,051 min
  5. 5Availability with no redundancy= 99.7004
  6. 6Availability of a redundant service= 99.99998

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 5 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why is my SLA worse than every provider's?

Because they multiply. Each additional hard dependency subtracts from your achievable availability, which is why graceful degradation matters more than provider SLAs.

Does provider SLA equal actual availability?

No. SLAs are financial commitments with exclusions, not predictions. Observed availability is usually better than the SLA, but the SLA is what you can plan against.

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