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Calculating Solution Service Level Agreement

The requirement for the web application is that the combined service level agreement for all components in the hot path is greater than 99.9%. The components in the hot path comprise of any service that is used in fulfilling a web request from a user.

Development

With a development environment, network isolation is not used. The following services are considered:

Service Azure SLA
Azure Front Door 99.990%
Entra ID 99.990%
Azure App Service 99.950%
Redis Cache 99.900%
Azure SQL 99.995%
Azure Storage 99.900%
Key Vault 99.990%
App Configuration 99.900%
Combined SLA 99.616%

Production - Single Region

When operating in production, network isolation is used. We do not consider the availability of the hub resources or VNET peering.

Service Azure SLA
Azure Front Door 99.990%
Entra ID 99.990%
Private DNS Zone 100.00%
AFD Private Link 99.990%
Azure App Service 99.950%
- Private Link 99.990%
Redis Cache 99.900%
- Private Link 99.990%
Azure SQL 99.995%
- Private Link 99.990%
Azure Storage 99.900%
- Private Link 99.990%
Key Vault 99.990%
- Private Link 99.990%
App Configuration 99.900%
- Private Link 99.990%
Combined SLA 99.546%

Production - Two Regions

Since the single region SLA is less than the requested 99.9% availability, we have to deploy to two regions. Azure Front Door, Entra ID, and Private DNS Zones are shared resources. However, the rest of the services can be doubled up for more reliability.

Service Azure SLA
Shared Services
Azure Front Door 99.990%
Entra ID 99.990%
Private DNS Zone 100.00%
Regional Services
AFD Private Link 99.990%
Azure App Service 99.950%
- Private Link 99.990%
Redis Cache 99.900%
- Private Link 99.990%
Azure SQL 99.995%
- Private Link 99.990%
Azure Storage 99.900%
- Private Link 99.990%
Key Vault 99.990%
- Private Link 99.990%
App Configuration 99.900%
- Private Link 99.990%
Shared Services 99.980%
Regional Services 99.546%
Combined SLA 99.9779%

Using dual regions will help us achieve the requested service level agreement.

For more information on how to calculate effective SLO, please refer to the Well Architected Framework.