Inconsistent Logs Between Kudu Log Stream and App Insights

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Inconsistent Logs Between Kudu Log Stream and App Insights

Camryn Friedman 0

I have an Azure Function App written in Java that I am trying to view logs for. For the past few months, I have had a hard time using the native "Log Stream" from Azure Portal, so my go-to log stream is by navigating to "Advanced Tools" (Kudu) and opening Log Stream from there. When I do that, I am able to see many Function App logs appear, as expected.

On the other hand, I also have App Insights configured for my app, with sampling disabled. In host.json I have set most of the log levels to Error in my host.json, but I have included an override in appsettings.json for one of them:

  {
    "name": "APPLICATIONINSIGHTS_ENABLE_AGENT",
    "value": "true",
    "slotSetting": false
  },
  {
    "name": "APPLICATIONINSIGHTS_INSTRUMENTATION_LOGGING_LEVEL",
    "value": "INFO",
    "slotSetting": false
  },
  {
    "name": "AzureFunctionsJobHost__logging__LogLevel__Function",
    "value": "Information",
    "slotSetting": false
  },

As my function is written, it is an Event Hub trigger that simply prints out the received event in the form of a log via the ExecutionContext logger, and does no further processing. There is 1 line of code that logs the event and that is it. I can see all of these event logs in the Log Stream, as mentioned before. However, not all of them are showing up in App Insights.

I have spent time with GitHub Copilot having it analyze my source code along with appsettings.json and host.json files, and I am completely stuck. This log prints out sometimes in App Insights, but other times it does not. Does anyone have any suggestions?

Pravallika KV 2,690 Reputation points Microsoft External Staff Moderator

2025-12-03T22:39:08.83+00:00
Hi Camryn Friedman,

Thanks for reaching out to Microsoft Q&A.

Could you please provide your host.json?

In your host.json, ensure the log level set accurately reflects what you want to capture. Though you have specified the log level for your functions in appsettings.json, host.json log level settings can also control visibility:

{ "logLevel": { "Default": "Information", "Function": "Information" } }

Ensure that both APPINSIGHTS_INSTRUMENTATIONKEY orAPPLICATIONINSIGHTS_CONNECTION_STRING are correctly set in your App Settings.

Consider running an Analytics query in Application Insights to check if some logs are being sampled:

union requests, dependencies, pageViews, browserTimings, exceptions, traces | where timestamp > ago(7d) | summarize TelemetrySavedPercentage = 100 / avg(itemCount) by bin(timestamp, 1d), itemType | sort by timestamp asc

If the TelemetrySavedPercentage is below 100, it indicates some telemetry is being dropped due to sampling.

Camryn Friedman 0

Hi @Pravallika KV ! Thanks for your suggestions, I'll run that Analytics query to check. I've made sure that the APPINSIGHTS_INSTRUMENTATIONKEY is correct. Here's the host.json. As mentioned, I set the levels to Error with intention to override them using appsettings so that I don't need a redeployment to change the appsetting (I can just update the configuration in Environment Variables in the Portal). Thanks for any further assistance.

{
  "version": "2.0",
  "logging": {
    "logLevel": {
      "default": "Error",
      "Function": "Error",
      "Host.Aggregator": "Error",
      "Host.Results": "Error",
      "Azure.Storage.Blobs": "Error",
      "Azure.Core": "Error",
      "Azure.Messaging.EventHubs": "Error",
      "System.Net.Http": "Error",
      "com.microsoft.aad.msal4j": "Error",
      "com.azure.identity": "Error",
      "Microsoft.Azure.WebJobs.EventHubs": "Error"
    },
    "applicationInsights": {
      "samplingSettings": {
        "isEnabled": false,
        "maxTelemetryItemsPerSecond": 20,
        "initialSamplingPercentage": 100.0,
        "minSamplingPercentage": 0.1,
        "maxSamplingPercentage": 75.0,
        "excludedTypes": "Dependency;Event;PageView;Request"
      }
    }
  },
  "extensions": {
    "kafka": {
      "autoOffsetReset": "Latest",
      "maxBatchSize": 10,
      "SubscriberIntervalInSeconds": 3,
      "ExecutorChannelCapacity": 10,
      "ChannelFullRetryIntervalInMs": 50,
      "MaxPollIntervalMs": 1200000,
      "AutoCommitIntervalMs": 1000
    }
  },
  "extensionBundle": {
    "id": "Microsoft.Azure.Functions.ExtensionBundle",
    "version": "[4.0.0, 5.0.0)"
  }
}

Your answer

Pravallika KV 2,690 Reputation points Microsoft External Staff Moderator

2025-12-03T22:39:08.83+00:00

Hi Camryn Friedman,

Thanks for reaching out to Microsoft Q&A.

Could you please provide your host.json?

In your host.json, ensure the log level set accurately reflects what you want to capture. Though you have specified the log level for your functions in appsettings.json, host.json log level settings can also control visibility:

{ "logLevel": { "Default": "Information", "Function": "Information" } }

Ensure that both APPINSIGHTS_INSTRUMENTATIONKEY orAPPLICATIONINSIGHTS_CONNECTION_STRING are correctly set in your App Settings.

Consider running an Analytics query in Application Insights to check if some logs are being sampled:

union requests, dependencies, pageViews, browserTimings, exceptions, traces | where timestamp > ago(7d) | summarize TelemetrySavedPercentage = 100 / avg(itemCount) by bin(timestamp, 1d), itemType | sort by timestamp asc

If the TelemetrySavedPercentage is below 100, it indicates some telemetry is being dropped due to sampling.
Camryn Friedman 0 Reputation points

2025-12-04T16:40:03.7433333+00:00

Hi @Pravallika KV ! Thanks for your suggestions, I'll run that Analytics query to check. I've made sure that the APPINSIGHTS_INSTRUMENTATIONKEY is correct. Here's the host.json. As mentioned, I set the levels to Error with intention to override them using appsettings so that I don't need a redeployment to change the appsetting (I can just update the configuration in Environment Variables in the Portal). Thanks for any further assistance.

{ "version": "2.0", "logging": { "logLevel": { "default": "Error", "Function": "Error", "Host.Aggregator": "Error", "Host.Results": "Error", "Azure.Storage.Blobs": "Error", "Azure.Core": "Error", "Azure.Messaging.EventHubs": "Error", "System.Net.Http": "Error", "com.microsoft.aad.msal4j": "Error", "com.azure.identity": "Error", "Microsoft.Azure.WebJobs.EventHubs": "Error" }, "applicationInsights": { "samplingSettings": { "isEnabled": false, "maxTelemetryItemsPerSecond": 20, "initialSamplingPercentage": 100.0, "minSamplingPercentage": 0.1, "maxSamplingPercentage": 75.0, "excludedTypes": "Dependency;Event;PageView;Request" } } }, "extensions": { "kafka": { "autoOffsetReset": "Latest", "maxBatchSize": 10, "SubscriberIntervalInSeconds": 3, "ExecutorChannelCapacity": 10, "ChannelFullRetryIntervalInMs": 50, "MaxPollIntervalMs": 1200000, "AutoCommitIntervalMs": 1000 } }, "extensionBundle": { "id": "Microsoft.Azure.Functions.ExtensionBundle", "version": "[4.0.0, 5.0.0)" } }

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Inconsistent Logs Between Kudu Log Stream and App Insights

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