Azure Functions Concepts
Azure Functions is a serverless compute service that lets you run code on demand without explicitly provisioning or managing infrastructure. With Azure Functions, you can build applications by using readily available triggers and services, allowing you to process and react to events. This document provides an overview of the core concepts behind Azure Functions.
Key Concepts
Functions
A function is a piece of code that is triggered by a specific event. Each function consists of a single piece of code that performs a specific task. Functions are typically small and focused, making them easy to write, deploy, and manage.
Triggers
A trigger defines how a function is invoked. It's the event that starts the execution of a function. Azure Functions supports a wide variety of triggers, including:
- HTTP Trigger: Invokes a function via an HTTP request.
- Timer Trigger: Invokes a function on a schedule.
- Blob Trigger: Invokes a function when a blob is created or updated in Azure Blob Storage.
- Queue Trigger: Invokes a function when a message is added to an Azure Storage Queue.
- Event Grid Trigger: Invokes a function in response to events from Azure Event Grid.
- Cosmos DB Trigger: Invokes a function when documents are created or updated in Azure Cosmos DB.
When a trigger event occurs, the Azure Functions runtime executes the associated function.
Bindings
Bindings allow your function to connect to other Azure services and external data sources without having to write complex integration code. Bindings simplify data input and output for your functions. They come in two main types:
- Input Bindings: Provide data to your function from an external source.
- Output Bindings: Send data from your function to an external service.
For example, you can use an input binding to read a message from a queue and an output binding to write a result to a database. Bindings are declared in the function's configuration file (e.g., function.json or via attributes in code).
Runtime
The Azure Functions runtime is the software that executes your functions. It manages function execution, handles triggers, manages bindings, and provides logging and monitoring capabilities. The runtime can be hosted in various environments, including Azure (Consumption plan, Premium plan, App Service plan) and your local machine.
Consumption Plan
The Consumption plan is a fully managed serverless hosting option for Azure Functions. You pay only for the time your code runs. The platform automatically scales your application based on demand, from zero to thousands of requests per second. This plan is ideal for event-driven workloads and applications with intermittent or unpredictable traffic.
Premium Plan
The Azure Functions Premium plan offers enhanced capabilities over the Consumption plan, including pre-warmed instances for faster cold starts, VNet connectivity, and longer run durations. It provides a balance between serverless flexibility and dedicated resource predictability.
App Service Plan
You can also run Azure Functions on an Azure App Service plan. This provides a dedicated environment for your functions, offering more control over resources and pricing. This is suitable for applications that already run on App Service or require consistent performance.
Host.json
The host.json file is used to configure the behavior of the Azure Functions host. It controls settings like logging levels, HTTP endpoint behavior, and extension configurations. You can find detailed information about its schema in the official Azure Functions documentation.
Next Steps
To learn more about building Azure Functions, explore the following resources: