Here is a really cool App Analytics query over App Insights that shows the request failure ratio of your app over the last week.
I use “extend” with the “iff” features to create a a successes field I can count, and then use “extend” again to create a failure ratio.
| where timestamp > ago(7d)
| extend isSuccesss=iff(success=="True" ,1, 0)
| summarize failures=sum(1-isSuccesss) , successes=sum(isSuccesss)
by timestamp bin=20m
| extend ratio=todouble(failures) / todouble(failures+successes)
| project timestamp, failure_Percent=ratio*100
| render timechart