Application Insights: Missing telemetry from FunctionApp-Investigation and Next Steps

Question

Application Insights: Missing telemetry from FunctionApp-Investigation and Next Steps

Jeff Hoffman 0

Problem description

I have a production Azure Function App running Python 3.12 on Flex Consumption in Central US. The Function App executes successfully, but standard Application Insights telemetry from the Function runtime is not appearing in the configured, workspace-based Application Insights resource.

Function App diagnostic logs are successfully reaching Log Analytics, and Azure Monitor platform metrics independently confirm Function executions. However, the corresponding Application Insights telemetry is absent, including requests, traces, dependencies, exceptions, and custom events.

Environment

Azure Functions Flex Consumption
Linux / Python 3.12
Region: Central US
Workspace-based Application Insights
System-assigned managed identity
Application Insights connection string configured
Function App VNet integration enabled
Application Insights ingestion uses the regional centralus-2.in.applicationinsights.azure.com endpoint

The Functions host reports:

TelemetryMode: ApplicationInsights
ApplicationInsightsLoggerProvider successfully initialized

Troubleshooting completed

Application Insights backend/ingestion

Microsoft's Application Insights Telemetry Flow Diagnostic completed 27 checks with 0 failures and 0 warnings.

A synthetic telemetry record was submitted directly to the configured Application Insights ingestion endpoint and:

Returned HTTP 200
Was accepted by the ingestion service
Was subsequently confirmed as stored and queryable in Application Insights

This indicates that the target Application Insights resource and backend ingestion/storage path are operational.

Function execution validation

Function executions have been independently confirmed using Azure Monitor's OnDemandFunctionExecutionCount metric.

For example, during one controlled test, executions were recorded at:

2026-10-07 14:58 UTC
2026-10-07 15:04 UTC

No corresponding records appeared in the workspace-backed Application Insights tables (AppRequests, AppTraces, AppDependencies, AppExceptions, or AppEvents).

Host logging and sampling

A temporary host.json configuration was deployed with:

default = Information
Host.Results = Information
Function = Information
Host.Aggregator = Trace
Application Insights sampling disabled

The deployed host.json was verified directly in the Function App, and Function App logs showed that the host loaded the updated logging configuration.

This did not restore Application Insights telemetry.

Authentication test

The Function App normally uses:

APPLICATIONINSIGHTS_AUTHENTICATION_STRING=Authorization=AAD

with a system-assigned managed identity that has the appropriate Application Insights RBAC assignment.

As a diagnostic test:

APPLICATIONINSIGHTS_AUTHENTICATION_STRING was temporarily removed.
APPLICATIONINSIGHTS_CONNECTION_STRING was retained.
The Function App was restarted.
Two new Function executions were performed and independently confirmed through Azure Monitor metrics.

No standard Application Insights telemetry appeared.

Startup logs also showed no Unauthorized, Forbidden, or AAD authentication errors.

The AAD authentication setting was subsequently restored.

Python dependencies

The deployed requirements.txt was reviewed and does not explicitly contain:

azure-monitor-opentelemetry
opentelemetry-api
opentelemetry-sdk
opentelemetry-instrumentation-*
applicationinsights
opencensus-*

Therefore, no explicit competing telemetry SDK from this list has been identified.

Runtime

The effective Flex configuration reports:

Runtime: Python
Version: 3.12

FUNCTIONS_EXTENSION_VERSION is not explicitly configured. My understanding from Microsoft's Flex Consumption documentation is that Flex Consumption uses the Functions v4 runtime and does not use FUNCTIONS_EXTENSION_VERSION to pin/select the Functions runtime version.

Networking

The Function App uses VNet integration. Effective Flex configuration reports:

outboundVnetRouting.allTraffic = false
outboundVnetRouting.applicationTraffic = false
outboundVnetRouting.managedIdentityTraffic = false

The successful synthetic ingestion test originated outside the Function worker environment, so it does not conclusively validate connectivity from the actual Flex Consumption worker.

Current status / question

The current evidence appears to isolate the problem to standard Application Insights telemetry not being emitted/exported from the Function App runtime/worker, rather than a general Application Insights backend ingestion failure:

Function executions are independently confirmed.
Function diagnostic logs reach Log Analytics.
The Functions host initializes Application Insights logging.
Direct synthetic Application Insights ingestion succeeds.
Host logging/sampling changes do not resolve the issue.
Removing AAD/managed-identity telemetry authentication does not resolve the issue.
No explicit competing Python telemetry SDK has been identified.

What is the Microsoft-supported method for validating DNS resolution and HTTPS/TCP 443 connectivity to the configured Application Insights ingestion endpoint from the actual Flex Consumption worker environment?

Also, are there any known issues or additional requirements affecting standard Application Insights telemetry emission for Python 3.12 Function Apps on Flex Consumption?

Rakesh Mishra 11,430 Reputation points Microsoft External Staff Moderator

2026-10-08T09:14:05.3566667+00:00

Hi @Jeff Hoffman , Thank you for reaching out to Microsoft Q&A portal. I am looking into the issue and will reach out to you on this.

1 answer

Your answer

Rakesh Mishra 11,430 Reputation points Microsoft External Staff Moderator

2026-10-08T09:14:05.3566667+00:00

Hi @Jeff Hoffman , Thank you for reaching out to Microsoft Q&A portal. I am looking into the issue and will reach out to you on this.

Answer 1

Hello @Jeff Hoffman

Your testing confirms that the Application Insights resource and ingestion endpoint can accept telemetry, but the synthetic test performed outside the Function App does not validate connectivity from the actual Flex Consumption worker. This requires the connectivity test to run from the application host.

For a VNet-integrated Function App, it requires outbound HTTPS/TCP 443 access to these Application Insights endpoints:

dc.applicationinsights.azure.com

dc.applicationinsights.microsoft.com

dc.services.visualstudio.com

*.in.applicationinsights.azure.com

This includes your regional centralus-2.in.applicationinsights.azure.com endpoint.

The supported next step is to open Function App > Diagnose and solve problems and run the “Function App missing telemetry Application Insights or OpenTelemetry” diagnostic workflow.

Test the DNS and HTTPS connectivity from the application host. If Flex Consumption does not expose an interactive worker console for this app, an external curl or synthetic-ingestion test is not an equivalent worker-path test. In that situation, Azure Support would need to inspect the worker’s DNS resolution, outbound connection to port 443, and Functions host telemetry-exporter logs.

Python 3.12 is supported on Flex Consumption. Flex Consumption also does not support pinning the Functions host through FUNCTIONS_EXTENSION_VERSION; it runs a platform-managed supported host version.

For standard Functions host telemetry, an explicit Python Application Insights or OpenTelemetry package is not required when using the built-in Application Insights integration. Application packages are required when the application itself emits custom telemetry or when you intentionally configure OpenTelemetry-based instrumentation.

Also, AppDependencies, AppExceptions, and AppEvents are not necessarily populated for every successful invocation. However, the complete absence of host request/trace telemetry while executions are confirmed is not expected under the documented configuration.

There's no verified official documentation identifying a known general issue specifically affecting standard Application Insights telemetry on Python 3.12 Flex Consumption in Central US.

Given the evidence already collected, I recommend opening an Azure support case and supplying:

The two exact UTC invocation times.
Function App, Application Insights, and Log Analytics resource IDs.
The effective host.json and application settings.
The Functions host initialization messages.
The completed telemetry-flow diagnostic results.
The regional ingestion hostname.
Confirmation that the external ingestion test succeeded but that no test has yet run inside the actual worker.

Microsoft Support should specifically verify the worker’s telemetry-export pipeline and outbound path to centralus-2.in.applicationinsights.azure.com:443.

References:

Application Insights logs are missing or incorrect for Azure Function App

Troubleshoot missing application telemetry in Application Insights

Configure monitoring for Azure Functions

Azure Functions Flex Consumption plan

Target Azure Functions runtime versions

Microsoft Entra authentication for Application Insights

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