Lab 04: Browser ↔ server correlation

Timebox: 15 min — Confirm one operation_Id end-to-end.

This lab is the payoff for Labs 02 and 03. It is a structured walkthrough of how to confirm end-to-end correlation in Application Insights, plus a debugging workflow for when correlation breaks.

Learning Objectives

By the end of this lab you will be able to:

• Trigger a deterministic, easily-findable transaction from the browser.
• Locate the resulting four spans (PageView, AJAX dependency, API request, SQL dependency) in Transaction Search.
• Run a KQL union query that returns all four rows for a given operation_Id.
• Diagnose the three most common correlation breakages: missing JS SDK, missing CORS exposure, and a misconfigured distributedTracingMode.

Exercises

Exercise 4.1: Generate a known transaction

In the browser, perform a search for postalCode=G1V. The search box automatically appends a unique q query-string parameter so this transaction is easy to find later.

Exercise 4.2: Find the operation_Id from PageView

In Application Insights → Logs:

pageViews
| where timestamp > ago(10m)
| where url contains "postalCode=G1V"
| project timestamp, name, url, operation_Id
| top 1 by timestamp desc

Copy the returned operation_Id into your scratch buffer.

Exercise 4.3: Confirm all four spans correlate

let opId = "<paste-operation_Id-here>";
union
    (pageViews | where operation_Id == opId | extend kind = "pageView"),
    (dependencies | where operation_Id == opId | extend kind = "dependency"),
    (requests | where operation_Id == opId | extend kind = "request")
| project timestamp, kind, name, target, duration, success
| order by timestamp asc

Expected output (in order):

1. pageView — the search page render.
2. dependency (Ajax) — GET $API_URI/establishments.
3. request — the API endpoint that handled the call.
4. dependency (SQL) — the EF Core query against dbo.Establishments.

Exercise 4.4: Break it deliberately, then fix it

Comment out WithExposedHeaders in the API CORS policy from Lab 03, redeploy, and re-run Exercise 4.3. The AJAX dependency now appears under a different operation_Id from the API request — confirming the failure mode and reinforcing why exposing the W3C headers is non-negotiable.

Restore the line and confirm correlation returns.

Verification Checkpoint

• You can name and recognize all four span types in the union query above.
• You ran the deliberate breakage and saw the orphaned AJAX dependency.
• You restored the CORS exposure and confirmed correlation returns.
• You can articulate the difference between operation_Id (per trace) and operation_ParentId (per span).

Next Steps

End-to-end correlation is now demonstrably working. Continue with Lab 05: Dashboards, KQL, alerts to turn this telemetry into a Workbook, three KQL queries and one alert rule.