Function Compute:HTTP Trigger Overview

Trigger limits

• You can create at most one HTTP trigger per version or alias. For more information, see Version management and Alias management.

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

  Note

  To host website-style services publicly, use an ICP-filed custom domain name. Bind the domain name to your function before exposing it. For more information, see Configure a custom domain name.

HTTP/HTTPS protocol limits

• HTTP request limits

  • Custom request headers that start with x-fc- are not supported. The following custom headers are also unsupported:

    • connection

    • keep-alive

  • If a request exceeds any of the following limits, Function Compute returns HTTP status code 400 and error code InvalidArgument.

    • Header size: The combined size of all header keys and values must not exceed 8 KB.

    • Path size: The total size of the path, including all query parameters, must not exceed 4 KB.

    • Body size: For synchronous invocations, the request body must not exceed 32 MB. For asynchronous invocations, refer to Function execution resource limits.

• HTTP response limits

  • Custom response headers that start with x-fc- are not supported. The following custom headers are also unsupported:

    • connection

    • content-length

    • date

    • keep-alive

    • server

    • upgrade

    • content-disposition:attachment

      Note

      For security, Function Compute adds content-disposition: attachment to response headers when you use the default Function Compute domain name (aliyuncs.com). This causes browsers to download responses as attachments. To remove this behavior, configure a custom domain name. For more information, see Configure a custom domain name.

  • If a response exceeds the following limit, Function Compute returns HTTP status code 502 and error code BadResponse.

    • Header size: The combined size of all header keys and values must not exceed 8 KB.

Synchronous invocation

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

Asynchronous invocation

In asynchronous invocation, Function Compute persists the request and returns a response immediately, without waiting for the function to finish executing.

• Asynchronous invocation: Add the request header "X-Fc-Invocation-Type":"Async" to enable request-level asynchronous invocation.

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

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

After a successful asynchronous invocation, Function Compute returns HTTP status code 202, indicating the request was accepted. It also returns the request ID in the response header, for example: "X-Fc-Request-Id": "80bf7****281713e1".

Simple requests

Simple requests do not send preflight requests, so you can directly set headers that start with Access-Control-Allow-* in your function code to implement simple 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 set custom headers, Function Compute sets the following response headers by default, based on the corresponding request headers:

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

• Access-Control-Allow-Credentials: Default value is true.

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

Non-simple requests

Non-simple requests send a preflight request before the actual request. A non-simple request includes one OPTIONS method invocation and one actual function invocation. The rules for the actual request match those for simple requests. To customize the preflight response, add the OPTIONS method to your HTTP trigger and handle the OPTIONS request in your function code. Set response headers that start with Access-Control-Allow- to control cross-origin behavior.

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

For example, here is how to handle preflight requests in Node.js runtime code:

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 preflight requests
          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 available as an invitational preview. To enable it, contact us and provide your Alibaba Cloud account ID (UID).