Azure Functions Host Configuration

The Azure Functions host is responsible for managing the execution of your functions. You can configure its behavior and settings to suit your needs. This section covers the primary configuration options available for the Functions host.

Key Configuration Concepts

The host configuration is primarily defined in the host.json file. This file is located at the root of your function app project.

host.json Structure

The host.json file uses a JSON format and supports various top-level properties to control host behavior. Here's a basic example:

{
  "version": "2.0",
  "logging": {
    "applicationInsights": {
      "samplingSettings": {
        "isEnabled": true,
        "excludedTypes": "Request"
      }
    }
  },
  "extensionBundle": {
    "id": "Microsoft.Azure.Functions.ExtensionBundle",
    "version": "[3.*, 4.0.0)"
  },
  "extensions": {
    "http": {
      "routePrefix": "api"
    }
  }
}

Common Configuration Settings

• version: Specifies the version of the host.json schema. Typically set to "2.0".
• logging: Configures logging behavior, including integration with Application Insights.
• extensionBundle: Defines the extension bundle to use, which provides pre-compiled bindings.
• extensions: Configures specific binding extensions, such as the HTTP trigger.

Logging Configuration

Fine-tune your logging settings to capture the right amount of information for debugging and monitoring. The logging object within host.json controls this.

Application Insights Integration

The applicationInsights object within logging allows you to configure how your function app integrates with Azure Application Insights.

{
  "logging": {
    "applicationInsights": {
      "samplingSettings": {
        "isEnabled": true,
        "excludedTypes": "Request",
        "includedTypes": "Exception,Trace,Dependency",
        "percentage": 100
      },
      "enableLiveMetricsFilters": false
    },
    "logLevel": {
      "default": "Information",
      "Host.Startup": "Trace"
    }
  }
}

• samplingSettings: Control the sampling of telemetry data to reduce costs and noise.
• enableLiveMetricsFilters: Enable or disable live metrics filters in Application Insights.
• logLevel: Set the default logging level for your function app and specific categories. Supported levels include Trace, Debug, Information, Warning, Error, and Critical.

Extension Bundles

Extension bundles provide a way to include common binding extensions with your function app without manually installing them. They are managed by Azure.

Configuring extensionBundle

{
  "extensionBundle": {
    "id": "Microsoft.Azure.Functions.ExtensionBundle",
    "version": "[3.*, 4.0.0)"
  }
}

• id: The identifier for the extension bundle. The default is Microsoft.Azure.Functions.ExtensionBundle.
• version: The version range of the bundle to use. Using semantic versioning (e.g., [3.*, 4.0.0)) is recommended.

HTTP Trigger Configuration

You can customize how HTTP triggers behave, including setting a route prefix for all HTTP-triggered functions.

Configuring HTTP Extension

{
  "extensions": {
    "http": {
      "routePrefix": "api"
    }
  }
}

In this example, all HTTP-triggered functions will be prefixed with /api. So, a function with a route of /greet will be accessible at /api/greet.

Other Configuration Options

durableTask Settings

For Durable Functions, you can configure settings related to the underlying Durable Task Framework.

{
  "extensions": {
    "durableTask": {
      "hubName": "MyDurableTaskHub",
      "storageAccount": "AzureWebJobsStorage",
      "taskEvents": {
        "maxWriteStorageEvents": 1000,
        "maxReadStorageEvents": 1000
      }
    }
  }
}

customHandler

Configure custom handlers for languages not directly supported by Azure Functions. (Primarily for Linux Consumption plan).

{
  "customHandler": {
    "description": {
      "defaultExecutablePath": "node",
      "workingDirectory": "",
      "arguments": [
        "handler.js"
      ]
    },
    "enableForwardingHttpRequest": true
  }
}

Environment Variables

Many configuration settings, especially connection strings and sensitive information, should be managed using environment variables rather than hardcoding them in host.json. These can be set in the Azure portal for your function app.