In this article, you learn the high-level concepts surrounding triggers and bindings for functions.
Triggers cause a function to run. A trigger defines how a function is invoked, and a function must have exactly one trigger. Triggers can also pass data into your function, as you would with method calls.
Binding to a function is a way of declaratively connecting your functions to other resources. Bindings either pass data into your function (an input binding) or enable you to write data out from your function (an output binding) by using binding parameters. Your function trigger is essentially a special type of input binding.
You can mix and match bindings to suit your function's specific scenario. Bindings are optional, and a function might have one or multiple input and/or output bindings.
Triggers and bindings let you avoid hardcoding access to other services. Your function receives data (for example, the content of a queue message) in function parameters. You send data (for example, to create a queue message) by using the return value of the function.
Consider the following examples of how you could implement functions:
Example scenario Trigger Input binding Output binding A new queue message arrives, which runs a function to write to another queue. Queue* None Queue* A scheduled job reads Azure Blob Storage contents and creates a new Azure Cosmos DB document. Timer Blob Storage Azure Cosmos DB Azure Event Grid is used to read an image from Blob Storage and a document from Azure Cosmos DB to send an email. Event Grid Blob Storage and Azure Cosmos DB SendGrid* Represents different queues.
These examples aren't meant to be exhaustive, but they illustrate how you can use triggers and bindings together. For a more comprehensive set of scenarios, see Azure Functions scenarios.
Tip
Azure Functions doesn't require you to use input and output bindings to connect to Azure services. You can always create an Azure SDK client in your code and use it instead for your data transfers. For more information, see Connect to services.
Trigger and binding definitionsThe following example shows an HTTP-triggered function with an output binding that writes a message to an Azure Storage queue.
For C# class library functions, you configure triggers and bindings by decorating methods and parameters with C# attributes. The specific attribute that you apply might depend on the C# runtime model:
The HTTP trigger (HttpTrigger) is defined on the Run method for a function named HttpExample that returns a MultiResponse object:
[Function("HttpExample")]
public static MultiResponse Run([HttpTrigger(AuthorizationLevel.Function, "get", "post")] HttpRequestData req,
FunctionContext executionContext)
{
This example shows the MultiResponse object definition. The object definition returns HttpResponse to the HTTP request and writes a message to a storage queue by using a QueueOutput binding:
public class MultiResponse
{
[QueueOutput("outqueue",Connection = "AzureWebJobsStorage")]
public string[] Messages { get; set; }
public HttpResponseData HttpResponse { get; set; }
}
For more information, see the C# guide for isolated worker models.
The HTTP trigger (HttpTrigger) is defined on the Run method for a function named HttpExample. This function writes to a storage queue that the Queue and StorageAccount attributes define on the msg parameter:
[FunctionName("HttpExample")]
public static async Task<IActionResult> Run(
[HttpTrigger(AuthorizationLevel.Anonymous, "get", "post", Route = null)] HttpRequest req,
[Queue("outqueue"),StorageAccount("AzureWebJobsStorage")] ICollector<string> msg,
ILogger log)
{
For more information, see the C# guide for in-process models.
Legacy C# script functions use a function.json definition file. For more information, see the Azure Functions C# script (.csx) developer reference.
For Java functions, you configure triggers and bindings by annotating specific methods and parameters. This HTTP trigger (@HttpTrigger) is defined on the run method for a function named HttpTriggerQueueOutput. The function writes to a storage queue that the @QueueOutput annotation defines on the message parameter:
@FunctionName("HttpExample")
public HttpResponseMessage run(
@HttpTrigger(name = "req", methods = {HttpMethod.GET, HttpMethod.POST}, authLevel = AuthorizationLevel.ANONYMOUS)
HttpRequestMessage<Optional<String>> request,
@QueueOutput(name = "msg", queueName = "outqueue",
connection = "AzureWebJobsStorage") OutputBinding<String> msg,
final ExecutionContext context) {
context.getLogger().info("Java HTTP trigger processed a request.");
For more information, see the Java developer guide.
The way that you define triggers and bindings for Node.js functions depends on the specific version of Node.js for Azure Functions:
In Node.js for Azure Functions version 4, you configure triggers and bindings by using objects exported from the @azure/functions module. For more information, see the Node.js developer guide.
In Node.js for Azure Functions version 3, you configure triggers and bindings in a function-specific function.json file in the same folder as your code. For more information, see the Node.js developer guide.
The http method on the exported app object defines an HTTP trigger. The storageQueue method on output defines an output binding on this trigger.
const { app, output } = require('@azure/functions');
const queueOutput = output.storageQueue({
queueName: 'outqueue',
connection: 'MyStorageConnectionAppSetting',
});
app.http('httpTrigger1', {
methods: ['GET', 'POST'],
authLevel: 'anonymous',
extraOutputs: [queueOutput],
handler: async (request, context) => {
const body = await request.text();
context.extraOutputs.set(queueOutput, body);
return { body: 'Created queue item.' };
},
});
This example function.json file defines the HTTP trigger function that returns an HTTP response and writes to a storage queue:
{
"bindings": [
{
"type": "httpTrigger",
"direction": "in",
"authLevel": "function",
"name": "input"
},
{
"type": "http",
"direction": "out",
"name": "$return"
},
{
"type": "queue",
"direction": "out",
"name": "myQueueItem",
"queueName": "outqueue",
"connection": "MyStorageConnectionAppSetting"
}
]
}
The http method on the exported app object defines an HTTP trigger. The storageQueue method on output defines an output binding on this trigger.
import { app, HttpRequest, HttpResponseInit, InvocationContext, output } from '@azure/functions';
const queueOutput = output.storageQueue({
queueName: 'outqueue',
connection: 'MyStorageConnectionAppSetting',
});
export async function httpTrigger1(request: HttpRequest, context: InvocationContext): Promise<HttpResponseInit> {
const body = await request.text();
context.extraOutputs.set(queueOutput, body);
return { body: 'Created queue item.' };
}
app.http('httpTrigger1', {
methods: ['GET', 'POST'],
authLevel: 'anonymous',
extraOutputs: [queueOutput],
handler: httpTrigger1,
});
This example function.json file defines the HTTP trigger function that returns an HTTP response and writes to a storage queue:
{
"bindings": [
{
"type": "httpTrigger",
"direction": "in",
"authLevel": "function",
"name": "input"
},
{
"type": "http",
"direction": "out",
"name": "$return"
},
{
"type": "queue",
"direction": "out",
"name": "myQueueItem",
"queueName": "outqueue",
"connection": "MyStorageConnectionAppSetting"
}
]
}
This example function.json file defines the function:
{
"authLevel": "function",
"type": "httpTrigger",
"direction": "in",
"name": "Request",
"methods": [
"get",
"post"
]
},
{
"type": "http",
"direction": "out",
"name": "Response"
},
{
"type": "queue",
"direction": "out",
"name": "msg",
"queueName": "outqueue",
"connection": "AzureWebJobsStorage"
}
]
}
For more information, see the PowerShell developer guide.
The way that the function is defined depends on the version of Python for Azure Functions:
In Python for Azure Functions version 2, you define the function directly in code by using decorators:
app = func.FunctionApp(http_auth_level=func.AuthLevel.ANONYMOUS)
@app.route(route="HttpExample")
@app.queue_output(arg_name="msg", queue_name="outqueue", connection="AzureWebJobsStorage")
def HttpExample(req: func.HttpRequest, msg: func.Out [func.QueueMessage]) -> func.HttpResponse:
logging.info('Python HTTP trigger function processed a request.')
In Python for Azure Functions version 1, this example function.json file defines an HTTP trigger function that returns an HTTP response and writes to a storage queue:
{
"authLevel": "function",
"type": "httpTrigger",
"direction": "in",
"name": "Request",
"methods": [
"get",
"post"
]
},
{
"type": "http",
"direction": "out",
"name": "Response"
},
{
"type": "queue",
"direction": "out",
"name": "msg",
"queueName": "outqueue",
"connection": "AzureWebJobsStorage"
}
]
}
Not all services support both input and output bindings. See your specific binding extension for specific code examples for bindings.
Triggers and bindings are defined differently depending on the development language. Make sure to select your language at the top of this article.
Trigger and binding names are limited to alphanumeric characters and _, the underscore.
You can connect your function to other services by using input or output bindings. Add a binding by adding its specific definitions to your function. To learn how, see Add bindings to an existing function in Azure Functions.
Azure Functions supports multiple bindings, which must be configured correctly. For example, a function can read data from a queue (input binding) and write data to a database (output binding) simultaneously.
Supported bindingsThis table shows the bindings that are supported in the major versions of the Azure Functions runtime:
1 Support will end for version 1.x of the Azure Functions runtime on September 14, 2026. We highly recommend that you migrate your apps to version 4.x for full support.
2 Starting with the version 2.x runtime, all bindings except HTTP and timer must be registered. See Register Azure Functions binding extensions.
3 Triggers aren't supported in the Consumption plan. This binding type requires runtime-driven triggers.
4 This binding type is supported in Kubernetes, Azure IoT Edge, and other self-hosted modes only.
For information about which bindings are in preview or are approved for production use, see Supported languages.
Specific versions of binding extensions are supported only while the underlying service SDK is supported. Changes to support in the underlying service SDK version affect the support for the consuming extension.
Code examples for bindingsUse the following table to find more examples of specific binding types that show you how to work with bindings in your functions. First, choose the language tab that corresponds to your project.
Binding code for Python depends on the Python model version.
Custom bindingsYou can create custom input and output bindings. Bindings must be authored in .NET, but they can be consumed from any supported language. For more information about creating custom bindings, see Creating custom input and output bindings.
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