Function Compute:Web functions

Invocation methods

Function Compute supports two invocation methods:

How it works

Each invocation follows this sequence:

1. Receive a request — Function Compute receives an invocation from a client via an HTTP trigger, a custom domain name, or the InvokeFunction API.

2. Convert to HTTP — The request is converted into an HTTP request and forwarded to your HTTP server.

3. Process the request — Your server handles the request and returns an HTTP response.

4. Report execution status — Optionally set the x-fc-status response header to indicate whether the function succeeded or failed.

5. Return the response — Function Compute converts the HTTP response and returns it to the client.

Limitations

HTTP calls (recommended)

In passthrough mode, Function Compute forwards the client's HTTP request directly to your HTTP server and returns the server's response to the client. System-reserved fields are filtered out — see Request limits and Response limits.

API calls

When you invoke a function using the InvokeFunction API (via an SDK or event source), Function Compute converts the API request into an HTTP request before forwarding it to your server.

Report function execution status

Your HTTP server can report execution status to Function Compute using the x-fc-status response header. In the returned HTTP response, set both StatusCode and x-fc-status.

If `x-fc-status` is not set: Function Compute assumes the invocation succeeded. If an exception occurs but is not reported, Function Compute still considers the execution successful. This may not affect the business logic, but it impacts monitoring and observability.

If `x-fc-status` is set: When an exception occurs, Function Compute records the failure and prints the stack trace to the function logs.

Code example

The following Python example implements a minimal HTTP server using the Flask framework. Create a Web Function and select Python 3.10 as the runtime before running this code.

import os
from flask import Flask, request

REQUEST_ID_HEADER = 'x-fc-request-id'
app = Flask(__name__)


@app.route('/', defaults={'path': ''})
@app.route('/<path:path>', methods=['GET', 'POST', 'PUT', 'DELETE'])
def hello_world(path):
    # Get the request ID injected by Function Compute
    rid = request.headers.get(REQUEST_ID_HEADER)
    # Read the raw request body
    data = request.stream.read()
    print("Path: " + path)
    print("Data: " + str(data))
    # Return a response body, status code, and a custom header
    return "Hello, World!", 200, [('Function-Name', os.getenv('FC_FUNCTION_NAME'))]


if __name__ == '__main__':
    app.run(host='0.0.0.0', port=9000)

Key points:

• @app.route('/', defaults={'path': ''}) — handles requests to the root path.

• @app.route('/<path:path>', methods=['GET', 'POST', 'PUT', 'DELETE']) — handles dynamic paths for all supported HTTP methods; the path value is passed as the path argument.

• request.headers.get(REQUEST_ID_HEADER) — reads the x-fc-request-id header injected by Function Compute.

• request.stream.read() — reads the raw request body.

• return "Hello, World!", 200, [('Function-Name', os.getenv('FC_FUNCTION_NAME'))] — returns a 200 response with a Function-Name header sourced from the FC_FUNCTION_NAME environment variable.

What's next

• Manage versions

• Manage aliases

• Configure a custom domain name