Function Compute:HTTP Trigger Overview

Limits on triggers

• You can create only one HTTP trigger per function version or alias. For more information, see Manage versions and Manage aliases.

• Built-in domain names are for testing only. Do not use them for external production services because their stability is not guaranteed.

  Note

  To provide website services externally, use an ICP-filed custom domain name. Bind the domain to your function and serve traffic through that domain. For more information, see Configure a custom domain name.

Limits on HTTP(S)

• Limits on HTTP requests

  • Request headers do not support custom fields that start with x-fc- or the following fields:

    • connection

    • keep-alive

  • The system returns status code 400 and error code InvalidArgument if a request exceeds any of the following limits:

    • Headers size: The total size of all keys and values in headers cannot exceed 8 KB.

    • Path size: The total size of a path, including all query parameters, cannot exceed 4 KB.

    • Body size: The total body size of a synchronous invocation request cannot exceed 32 MB. For more information about the body size limit of asynchronous invocation requests, see Function execution resource limits.

• Limits on HTTP responses

  • Response headers do not support custom fields that start with x-fc- or the following fields:

    • connection

    • content-length

    • date

    • keep-alive

    • server

    • upgrade

    • content-disposition:attachment

      Note

      For security reasons, if you use the default aliyuncs.com domain name of Function Compute, the server adds the content-disposition: attachment header to response headers, which causes the browser to download the returned results as attachments. To remove this restriction, use a custom domain name. For more information, see Configure a custom domain name.

  • The system returns status code 502 and error code BadResponse if a response exceeds any of the following limits:

    • Headers size: The total size of all keys and values in headers cannot exceed 8 KB.

Synchronous invocation

In a synchronous invocation, the function processes the event and returns the result immediately. HTTP triggers use synchronous invocation by default. For more information, see Synchronous calls.

Asynchronous invocation

In an asynchronous invocation, Function Compute persists the request and returns a response immediately without waiting for execution to complete.

• Asynchronous invocation: Add the "X-Fc-Invocation-Type":"Async" request header to invoke a function asynchronously at the request level.

• Asynchronous tasks: After enabling asynchronous tasks for an HTTP function, add the "X-Fc-Async-Task-Id":"g6u*****iyvhd3jk8s6bhj0hh" request header to configure the invocation ID for the asynchronous task.

For more information about request headers, see Invoke a function.

After a successful asynchronous invocation, Function Compute returns status code 202. This indicates the request was received successfully. It also returns the request ID in the response header. The format is "X-Fc-Request-Id": "80bf7****281713e1".

Simple requests

A preflight request is not required for simple requests. You can set headers that start with Access-Control-Allow-* in your function code to implement basic access control. For simple requests, Function Compute supports the following custom headers: Access-Control-Allow-Origin, Access-Control-Allow-Headers, and Access-Control-Max-Age.

If you do not configure custom headers, Function Compute sets the following response headers by default:

• Access-Control-Allow-Origin: the Origin header of the request.

• Access-Control-Allow-Credentials: the default value is true.

• Access-Control-Expose-Headers: custom headers defined by Function Compute.

Non-simple requests

A non-simple request sends a preflight request before the actual request. A browser sends a preflight request using the OPTIONS method, then sends the actual request to invoke the function. Rules for non-simple requests match those for simple requests. To customize the preflight response, add the OPTIONS method to your HTTP trigger and process the OPTIONS request in your function code. Specifically, set headers that start with Access-Control-Allow-* to control cross-origin behavior.

For preflight requests, Function Compute supports the following custom headers: Access-Control-Allow-Origin, Access-Control-Allow-Headers, Access-Control-Allow-Methods, and Access-Control-Max-Age.

This example shows how to process preflight requests in function code using the built-in Node.js runtime:

exports.handler =  (event, context,callback) => {
      console.log('hello world');
      const method = JSON.parse(event).requestContext.http.method;
      if (method === 'OPTIONS') {
          // Set response headers to handle the preflight request.
          const fcResponse = {
            'statusCode': 204,
            'headers': {
              'Access-Control-Allow-Origin': 'http://www.fc.com',
              'Access-Control-Allow-Methods': 'POST',
              'Access-Control-Allow-Headers': 'Content-Type, Authorization',
              'Access-Control-Max-Age':'3600'
            },
            'body': 'hello world'
        };
        callback(null, fcResponse);
      } else {
        callback(null, {
            'statusCode': 500,
            'body': 'hello world'
        });
      }
    };

API Configured CORS

API Configured CORS is currently in invitational preview. To enable it, contact us and provide your Alibaba Cloud account ID (UID).