Define request success before interpreting Application Insights outcomes

Source facts

Application Insights request telemetry describes execution initiated by an incoming application request. Its required Success field treats requests as successful unless explicitly marked false. For web applications, the documented default classifies response codes below 400, and also 401, as successful. Microsoft cautions that this classification can differ from application semantics. Microsoft Learn.

The source gives contrasting examples: a 404 can represent an expected empty result or a broken link; a redirect can fail a client that cannot follow it. A 206 response can indicate that only part of a submitted batch was processed successfully. Microsoft Learn.

Applicability

Use this review for Application Insights request telemetry for web applications. Keep the transport response, the recorded success value and the application’s intended outcome as separate evidence fields. This brief does not redefine HTTP status codes.

DSE recommendation

DSE recommends asking each application owner to describe success for its important request paths. Record expected empty results, authentication challenges, unsupported redirects and partial processing where applicable. Decide which cases require an explicit failure classification in instrumentation. Avoid applying one blanket status-code exception to unrelated operations merely to improve a dashboard percentage.

Verification

Exercise approved examples of each documented outcome in a test environment. Compare the actual response, recorded Success value and business result. Have the owner explain any deliberate difference. Preserve representative telemetry and the classification decision so a later instrumentation change can be checked against the same cases.

Official references

Microsoft Learn: Application Insights telemetry data model.