How to Configure Log Level for Azure Functions

Azure Functions is a serverless computing service that allows you to run code without having to manage servers, infrastructure, or scaling. You can use Azure Functions to create various types of applications, such as web APIs, event-driven workflows, data processing, and more.

One of the benefits of Azure Functions is that it provides built-in logging capabilities that allow you to monitor and troubleshoot your functions. You can use the ILogger interface to write logs from your function code, and use the host.json file to configure the log level and other settings for your function app.

In this post, we will show you how to configure log level for Azure Functions using the host.json file. This can help you control the amount and detail of logs that are generated by your functions.

Prerequisites

Before we start, make sure you have the following:

An Azure account with an active subscription. You can create one for free here.
An Azure Function app with at least one function. You can follow this tutorial to create one.
Visual Studio Code with the Azure Functions extension installed. You can download it here and install the extension from the Extensions tab.
A basic understanding of JSON syntax and Azure Functions concepts. You can learn more here.

Configuring Log Level for Azure Functions

To configure log level for Azure Functions, we need to do the following steps:

Open your function app project in Visual Studio Code.
Locate the host.json file in the root folder of your project. This file contains configuration settings that apply to all functions in your function app.
Edit the host.json file to add or modify the logging section. This section allows you to specify the log level and other settings for your function app.
Save and deploy your changes to your function app.

Here is an example of how to do this in JSON:

{
  "version": "2.0",
  "logging": {
    // This setting controls the default log level for all categories
    "logLevel": {
      "default": "Information"
    },
    // This setting allows you to override the log level for specific categories
    "logLevelOverrides": {
      // This setting sets the log level for the host category to Error
      "Host": "Error",
      // This setting sets the log level for the function category to Trace
      "Function": "Trace"
    },
    // This setting controls whether to enable console logging
    "console": {
      "isEnabled": true
    },
    // This setting controls whether to enable application insights logging
    "applicationInsights": {
      "samplingSettings": {
        // This setting controls whether to enable adaptive sampling
        "isEnabled": true,
        // This setting controls the maximum number of telemetry items per second
        "maxTelemetryItemsPerSecond": 5
      }
    }
  }
}

{

"version": "2.0",

"logging": {

// This setting controls the default log level for all categories

"logLevel": {

"default": "Information"

// This setting allows you to override the log level for specific categories

"logLevelOverrides": {

// This setting sets the log level for the host category to Error

"Host": "Error",

// This setting sets the log level for the function category to Trace

"Function": "Trace"

// This setting controls whether to enable console logging

"console": {

"isEnabled": true

// This setting controls whether to enable application insights logging

"applicationInsights": {

"samplingSettings": {

// This setting controls whether to enable adaptive sampling

"isEnabled": true,

// This setting controls the maximum number of telemetry items per second

"maxTelemetryItemsPerSecond": 5

}

Conclusion

In this post, we have shown you how to configure log level for Azure Functions using the host.json file. This can help you control the amount and detail of logs that are generated by your functions.

If you have any questions or feedback, please leave a comment below.