Azure Functions is a serverless compute service that enables you to run code without provisioning or managing infrastructure. With Azure Functions, you can build applications by writing code in your preferred language and benefit from automatic scaling and pay-per-execution pricing.
Key Concepts
Functions
A function is the basic unit of work in Azure Functions. It's a piece of code that runs in response to an event. Functions can be written in various languages including C#, Java, JavaScript, Python, PowerShell, and TypeScript.
Each function has a trigger that defines how it's invoked and zero or more bindings that connect it to other services.
Triggers
A trigger is an Azure resource that defines how a function is invoked. When the event associated with a trigger occurs, the Azure Functions runtime executes the function. Common triggers include:
- HTTP Trigger: Invoked by an HTTP request.
- Timer Trigger: Invoked on a schedule (e.g., every hour).
- Blob Trigger: Invoked when a new or updated blob is detected in Azure Blob Storage.
- Queue Trigger: Invoked when a message is added to an Azure Storage Queue.
- Event Grid Trigger: Invoked in response to events from Event Grid topics.
- Service Bus Trigger: Invoked when a message arrives in an Azure Service Bus Queue or Topic.
A function must have exactly one trigger.
Bindings
Bindings allow your function to easily declare connections to other Azure services and to external data sources. Bindings can be used to:
- Input Bindings: Provide data to your function.
- Output Bindings: Send data from your function to another service.
Bindings simplify your code by abstracting away the details of connecting to and interacting with other services. You can have zero or more input and output bindings for a single function.
Runtime
The Azure Functions runtime manages the execution of your functions. It handles event processing, scaling, and connections to triggers and bindings. The runtime is available in two primary hosting models:
- Consumption Plan: You pay only for the time your code runs, with automatic scaling.
- Premium Plan: Offers pre-warmed instances, VNet connectivity, and longer runtimes for predictable performance.
- App Service Plan: Run your functions on the same infrastructure as your App Service apps.
Statelessness vs. Statefulness
By default, Azure Functions are stateless. This means each execution is independent of previous executions. However, you can implement stateful workflows using Azure Durable Functions, which allow you to write stateful functions in a serverless environment.
Durable Functions
Durable Functions is an extension of Azure Functions that enables you to write stateful, long-running orchestrations in a serverless environment. It allows you to implement patterns like:
- Function chaining
- Fan-out/fan-in
- Async HTTP APIs
- Monitors
- Human interaction
Development Experience
You can develop Azure Functions locally using tools like Visual Studio, Visual Studio Code, or the Azure Functions Core Tools. These tools allow you to develop, test, and debug your functions on your local machine before deploying them to Azure.
Azure Functions offers a powerful and flexible way to build event-driven applications and microservices without the overhead of managing infrastructure. Understanding these core concepts is crucial for effectively leveraging the service.