Gap-11: Functions Observe (B → A) — Invocation tracing + KQL query library#1643
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Gap-11: Functions Observe (B → A) — Invocation tracing + KQL query library#1643
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Pull request overview
Adds an Azure Functions observability reference focused on Application Insights, including invocation correlation concepts, Durable Functions telemetry notes, and a small KQL “query library” for common analyses.
Changes:
- Documented built-in Application Insights integration and the FunctionAppLogs table schema.
- Added guidance on invocation-level correlation (InvocationId/OperationId) and Durable Functions monitoring.
- Included 5 KQL examples plus notes on hosting plan sampling impacts and configuration.
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| | Telemetry Layer | What It Captures | Table | | ||
| |----------------|-----------------|-------| | ||
| | **Host-level** | Startup, scaling, worker health, binding execution | `traces`, `FunctionAppLogs` | | ||
| | **Function-level** | Invocation result, duration, trigger metadata | `requests`, `FunctionAppLogs` | | ||
| | **Custom SDK** | Dependencies, custom events, manual spans | `dependencies`, `customEvents` | |
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Markdown tables are written with a double leading pipe (|| ...), which renders as an extra empty column in most Markdown parsers. Use a single leading pipe (| ...) for the header and all rows (this pattern appears in multiple tables in this doc).
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| ## KQL Query Library | ||
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| ### Error rate by function name |
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This query returns an error count, not an error rate (there’s no denominator like total invocations/log volume per function per time bin). Either (a) rename the section/query to 'Error count', or (b) compute a rate/percentage by joining or summarizing total invocations (commonly from requests with success false/true) for the same FunctionName and time bin.
Suggested change
| ### Error rate by function name | |
| ### Error count by function name |
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| ## Invocation-Level Tracing | ||
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| Each function invocation gets a unique `InvocationId`. The runtime also assigns an `OperationId` that propagates to downstream calls: | ||
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| 1. Trigger fires → host assigns `InvocationId` + `OperationId` | ||
| 2. Function code executes → SDK-instrumented HTTP/DB calls inherit `OperationId` | ||
| 3. All telemetry (requests, dependencies, traces) correlates via `OperationId` |
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The doc uses multiple field name variants for the same concepts (e.g., InvocationId here vs FunctionInvocationId elsewhere, and OperationId here vs operation_Id in the Durable table). To reduce confusion when users copy queries, standardize on the exact column names per table (and explicitly map them when they differ), e.g., 'FunctionAppLogs: FunctionInvocationId / OperationId; requests/traces: operation_Id'.
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Details# 🔍 Token Analysis Report
fatal: path 'plugin/skills/appinsights-instrumentation/references/functions.md' exists on disk, but not in 'origin/main' 📊 Token Change ReportComparing Summary
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Consider moving content to
references/subdirectories.
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This was referenced Apr 2, 2026
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Closes #1619 | Parent: #1608
1 file: functions.md — FunctionAppLogs analysis, invocation-level tracing, Durable monitoring, 5 KQL queries (error rate, duration percentiles, cold starts), hosting plan sampling impact.