How to calculate service reliability and availability ?

Phani_5 

There is an example in the Log Analytics portal for HeartBeat data, which can start you - just adapt for App Insights.

I also have two posts that also may help form the basis of an SLA report (these are Log Analytics) but can be adjusted. 

https://blogs.msdn.microsoft.com/ukhybridcloud/2018/11/20/azure-log-analytics-service-level-agreement-sla-part-1/ 

and

https://blogs.msdn.microsoft.com/ukhybridcloud/2018/11/21/azure-log-analytics-service-level-agreement-part-2/