Azure Functions Runtime Reference

Runtime Reference

This section details the Azure Functions runtime, its capabilities, supported languages, versioning, and configuration options.

Runtime Overview

The Azure Functions runtime is the environment where your serverless functions execute. It manages function invocation, execution context, triggers, bindings, and logging. Understanding the runtime is crucial for developing, deploying, and managing your serverless applications effectively.

Key aspects of the runtime include:

• Event-driven execution: Functions are triggered by events from various Azure services or custom sources.
• Scalability: The runtime automatically scales the number of function instances based on demand.
• Language support: It supports multiple programming languages, allowing you to choose the best fit for your project.
• Extensibility: Through triggers and bindings, the runtime can integrate with a wide array of services.
• Configuration: Runtime behavior can be customized using configuration files.

Supported Languages

Azure Functions supports a variety of languages. The choice of language often depends on developer familiarity, existing codebases, and specific project requirements. The runtime provides a consistent experience across supported languages.

Runtime Versions

Azure Functions uses a versioned runtime. Staying updated with the latest runtime version is recommended to leverage new features, performance improvements, and security patches. You can specify the runtime version in your deployment configuration.

The current stable runtime versions are typically:

• v4: The latest major version, offering the most features and ongoing support.
• v3: An older stable version, still supported but may have feature limitations compared to v4.

For more details on specific version features and end-of-life dates, refer to the official Azure Functions documentation.

Runtime Configuration

The behavior of the Azure Functions runtime can be configured to meet your application's needs. This is primarily done through two configuration files:

• host.json: Configures the host and function runtime behavior.
• local.settings.json: Used for local development to define application settings and connection strings.

host.json

The host.json file is located at the root of your function app project. It allows you to configure settings that affect the function host. Some common configurations include:

• Logging: Control verbosity, sinks, and filtering.
• HTTP worker: Configure HTTP settings like request timeouts.
• Extensions: Manage and configure extension settings (e.g., Durable Functions, Event Grid).
• General: Settings like function timeouts, concurrency, and singleton behavior.

Example host.json:

{
  "version": "2.0",
  "logging": {
    "applicationInsights": {
      "samplingSettings": {
        "isEnabled": true,
        "excludedTypes": "Request"
      }
    }
  },
  "extensionBundle": {
    "id": "Microsoft.Azure.Functions.ExtensionBundle",
    "version": "[1.*, 2.0.0)"
  },
  "functionTimeout": "00:10:00",
  "concurrency": {
    "dynamicConcurrency": true
  }
}

local.settings.json

The local.settings.json file is used for local development and debugging. It stores application settings, connection strings, and feature flags that are not checked into source control.

• Values: Key-value pairs for application settings.
• ConnectionStrings: Connection strings for various services.
• IsEncrypted: Indicates if settings are encrypted.

When deployed to Azure, these settings are configured in the Function App's Application Settings.

Example local.settings.json:

{
  "IsEncrypted": false,
  "Values": {
    "AzureWebJobsStorage": "UseDevelopmentStorage=true",
    "FUNCTIONS_WORKER_RUNTIME": "dotnet",
    "MyCustomSetting": "LocalValue"
  },
  "ConnectionStrings": {
    "MyDatabase": "Server=localhost;Database=MyDb;Trusted_Connection=True;"
  }
}

This section provides a foundational understanding of the Azure Functions runtime. For in-depth details, please consult the official Azure documentation.