Why Are Azure Function Information Logs Missing in Logs Workspace?

Troubleshooting Missing Azure Function Logs in Application Insights

Working with Azure Functions often feels like building a well-oiled automation engine. But what happens when some crucial logs vanish from your Application Insights workspace? 🤔 It’s a challenge I recently faced while developing a Timer Trigger Azure Function. My Information-level logs, which worked perfectly in the Azure Portal log console, were mysteriously absent in the Logs workspace.

At first, I assumed everything was configured correctly. After all, I had set up Application Insights during the creation of my Function App, and the telemetry setup seemed to work out-of-the-box. As a developer, there’s nothing more puzzling than seeing Warning and Error logs appear correctly while Information logs are nowhere to be found. Where were they hiding?

This issue reminded me of a similar moment when debugging a web application. The error logs screamed “Fix me!” while the subtle Information-level logs slipped under the radar. It’s a bit like searching for a missing puzzle piece—knowing it exists but not quite seeing it in the pile. 🧩 Azure’s host.json and telemetry settings often play a role here.

In this article, I’ll break down the root cause of this issue and how to resolve it step by step. From host.json configurations to verifying log level thresholds, I’ll guide you through the solution. Let’s make sure those missing Information logs find their way back into your Logs workspace.

Understanding Missing Azure Function Logs and How to Solve It

The scripts provided earlier aim to resolve a common issue where Information-level logs generated by an Azure Function do not appear in the Logs workspace, even though they show up in the Azure Portal log console. This discrepancy often occurs due to improper configuration in the host.json file, insufficient telemetry settings, or issues with Application Insights integration. By using commands like ConfigureFunctionsWorkerDefaults() and AddApplicationInsightsTelemetryWorkerService(), we ensure that Application Insights captures the logs as expected. These scripts establish a strong foundation for collecting and managing telemetry data.

First, the `HostBuilder` in Program.cs sets up the Azure Function worker environment. The method ConfigureFunctionsWorkerDefaults() ensures that all required middleware for Azure Functions is initialized. It also allows custom logging and dependency injection configuration. Next, we explicitly register Application Insights using AddApplicationInsightsTelemetryWorkerService(). This step ensures that telemetry collection is correctly configured for non-HTTP-triggered Azure Functions. For instance, imagine debugging a Timer Trigger Function: Without Application Insights, tracking performance and identifying issues becomes a manual and time-consuming process. 🔧

The host.json file plays a key role in controlling what log levels are captured. By setting the `LogLevel` to Information in both the default and Application Insights sections, we explicitly define that Information-level logs must be processed. However, the samplingSettings property can sometimes filter out logs, leading to missing entries in the Logs workspace. By disabling sampling (`"isEnabled": false`), we ensure all telemetry data, including Information logs, is captured. This is particularly important when troubleshooting production issues where even minor details might reveal the root cause. I once faced a situation where a small LogInformation message helped uncover a misconfigured scheduler. 🎯

Finally, the unit test script verifies that logs at different levels—Information, Warning, and Error—are correctly emitted and captured. Using SetMinimumLevel(), we ensure the logger processes all logs at or above the desired threshold. In our example, we validated that Information logs appear when explicitly configured. Writing unit tests like this ensures that logging behavior is consistent across environments, preventing surprises during deployment. Together, these scripts provide a comprehensive solution to troubleshoot missing Azure Function logs and optimize telemetry collection in your cloud applications.

// Solution 1: Proper Host Configuration and Log Filtering
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Logging;
public class Program
{
    public static void Main(string[] args)
    {
        var host = new HostBuilder()
            .ConfigureFunctionsWorkerDefaults()
            .ConfigureServices(services =>
            {
                services.AddApplicationInsightsTelemetryWorkerService();
                services.Configure<LoggerFilterOptions>(options =>
                {
                    options.MinLevel = LogLevel.Information;
                });
            })
            .Build();
        host.Run();
    }
}

// host.json Configuration
{
  "version": "2.0",
  "logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft": "Warning",
      "Function": "Information"
    },
    "applicationInsights": {
      "LogLevel": {
        "Default": "Information"
      },
      "samplingSettings": {
        "isEnabled": false
      }
    }
  }
}

using Microsoft.Extensions.Logging;
public class MyFunction
{
    private readonly ILogger _logger;
    public MyFunction(ILoggerFactory loggerFactory)
    {
        _logger = loggerFactory.CreateLogger<MyFunction>();
    }
    public void Run()
    {
        _logger.LogInformation("Executing Information level log.");
        _logger.LogWarning("This is a Warning level log.");
        _logger.LogError("This is an Error level log.");
    }
}

using Xunit;
using Microsoft.Extensions.Logging;
public class LogTests
{
    [Fact]
    public void VerifyInformationLogsAreCaptured()
    {
        var loggerFactory = LoggerFactory.Create(builder =>
        {
            builder.AddConsole();
            builder.SetMinimumLevel(LogLevel.Information);
        });
        var logger = loggerFactory.CreateLogger("TestLogger");
        logger.LogInformation("This is a test Information log.");
        Assert.True(true, "Information log captured successfully.");
    }
}

Resolving Missing Azure Function Logs by Exploring Telemetry Data

Another critical aspect of Azure Function logs not appearing in the Logs workspace involves the telemetry channel configuration used by Application Insights. By default, Azure Functions use the Application Insights SDK, which buffers logs before sending them to the telemetry endpoint. This buffering, however, can delay or omit certain log entries like Information-level logs due to sampling or improper flushing of telemetry data. Ensuring proper telemetry channel behavior is crucial to maintaining consistent logs.

One often-overlooked factor is the samplingSettings configuration in host.json. When sampling is enabled, only a fraction of logs is sent to Application Insights to reduce data volume and costs. However, if Information logs are critical for debugging, you must either disable sampling completely (`"isEnabled": false`) or adjust the sampling logic to ensure all necessary logs are captured. For example, I faced an issue where enabling sampling caused random drops in non-critical Information logs, leading to frustration during production debugging. 💻

Additionally, using Flush commands ensures that all buffered telemetry is sent immediately, avoiding data loss. In scenarios where Azure Functions run under high-load triggers like HTTP requests or Timer triggers, telemetry buffering can accumulate quickly, causing delays. By explicitly calling TelemetryClient.Flush() or verifying telemetry endpoint connectivity, developers can reduce log inconsistencies and maintain an accurate monitoring environment. Ultimately, balancing sampling, buffering, and flushing allows for optimal log visibility while minimizing costs.

Ensuring Log Visibility in Azure Function Logs