Function Compute:Event handlers

Background information

For a custom container function in web server mode, Function Compute forwards the common headers, request body, POST method, and the /invoke and /initialize paths to the HTTP server in the container. You can use the function signatures, such as context and event, of runtimes supported by Function Compute, such as the Golang runtime. You can also use the request headers and body as input parameters to define the service logic of a function. For more information, see Event handlers.

For a custom container function in non-web server mode, Function Compute adds the body to the startup environment of the container by using environment variables. You can use os.GetEnv("FC_CUSTOM_CONTAINER_EVENT") to obtain event information and perform custom operations.

Function invocation

If a function in web server mode uses an event handler, the HTTP server needs to only implement the logic that corresponds to the /invoke path and the POST method.

Sample code for a custom container in web server mode

In the following Node.js Express example, the POST method and /initialize are called by Function Compute when a function instance is initialized. The POST method and /invoke serve as handlers when Function Compute is called. The context and event parameters are obtained from req.headers and req.body, and the results of the function invocation are then returned as an HTTP response.

'use strict';

const express = require('express');

// Constants.
const PORT = 9000;
const HOST = '0.0.0.0';
const app = express();
// Parse the JSON-formatted request body.
app.use(express.json({type:['application/json', 'application/octet-stream']}))


// The example of the Initializer hook. You must configure the Initializer hook when you create the function.
app.post('/initialize', (req, res) => {
  console.log(req.body)
  res.send('Hello FunctionCompute, /initialize\n');
});


// Invoke the event function.
app.post('/invoke', (req, res) => {
  console.log(req.body)
  res.send('Hello FunctionCompute, event function\n');
});

var server = app.listen(PORT, HOST);
console.log(`Running on http://${HOST}:${PORT}`);

server.timeout = 0; // Never time out.
server.keepAliveTimeout = 0; // keepalive, never timeout

Sample code for a custom container function in non-web server mode

In the following Python image example, the event-triggering content is obtained by using FC_CUSTOM_CONTAINER_EVENT.

import os

if __name__ == '__main__':
    FC_EVENT = os.environ['FC_CUSTOM_CONTAINER_EVENT']
    print("Hello serverless image")
    print("FC event is: " + FC_EVENT)

Examples

• Python

• C++

• Node.js

FAQ

• Must the listening port of a custom container runtime be the same as that of the HTTP server started in the custom container runtime?

• What do I do if the FunctionNotStarted error occurs when I invoke a third-party service in a service started in a custom container runtime?

• What do I do if a 502 error that contains the "Process exited unexpectedly before completing request" error message is returned?

• What do I do if a 404 error occurs when I use a browser or the cURL tool to access a function?

• What permissions must I grant to Function Compute service role if Alibaba Cloud public container images are not used?