Function Compute:Instance lifecycle hooks

Invoke code

After you configure an invoke code hook, the system sends an HTTP request to your function, such as POST /initialize or GET /pre-stop, when an instance starts or is about to stop. You must handle the request in your application code.

To use the Initializer hook in a custom image, your HTTP server must implement logic for the /initialize path and POST method. The same applies to the PreStop hook, which requires logic for the /pre-stop path and GET method. The following sample code shows an implementation for a custom Python 3.10 runtime.

import os
from flask import Flask
from flask import request

app = Flask(__name__)

@app.route('/initialize', methods=['POST'])
def init_invoke():
    rid = request.headers.get('x-fc-request-id')
    print("FC Initialize Start RequestId: " + rid)
    # do your things
    print("FC Initialize End RequestId: " + rid)
    return "OK"

@app.route('/', defaults={'path': ''})
@app.route('/<path:path>', methods=['GET', 'POST', 'PUT', 'DELETE'])
def hello_world(path):
    rid = request.headers.get('x-fc-request-id')
    print("FC invoke Start RequestId: " + rid)
    # do your things
    print("FC invoke End RequestId: " + rid)
    return "Hello, World!", 200, [('Function-Name', os.getenv('FC_FUNCTION_NAME'))]


@app.route('/pre-stop', methods=['GET'])
def prestop_invoke():
    rid = request.headers.get('x-fc-request-id')
    print("FC PreStop Start RequestId: " + rid)
    # do your things
    print("FC PreStop End RequestId: " + rid)
    return "OK"


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

The previous example shows a successful initialization. The following examples show how a /initialize hook can fail in Python.

@app.route('/initialize', methods=['POST'])
def init():
    raise Exception("hahaha")
    return "OK", 200, []

@app.route('/initialize', methods=['POST'])
def init():
    return "OK", 404, []

Execute instruction

An execute instruction hook runs a command to initialize the instance after it starts. You can use any shell supported by the function's runtime environment, such as /bin/bash, /bin/sh, /bin/csh, or /bin/zsh.

The Function Compute console provides two preset options: /bin/bash and /bin/sh. This topic uses /bin/sh as an example.

#!/bin/sh

URL="http://localhost:7860"
REQUEST_PATH="sdapi/v1/txt2img"
JSON_DATA='{
	"prompt": "",
	"steps": 1,
	"height": 8,
	"width": 8
}'
temp_file=$(mktemp)
trap 'rm -f "$temp_file"' EXIT

if ! http_code=$(curl -s -w "%{http_code}" \
	-H "Content-Type: application/json" \
	-d "$JSON_DATA" \
	-o "$temp_file" \
	-X POST "$URL"/"$REQUEST_PATH"); then
	echo "{\"status\": \"curl_error\", \"code\": $curl_exit_code}" \
	| jq . >&2
	exit 1
fi

response=$(<"$temp_file")
echo "http code $http_code"

if [ "$http_code" -eq 200 ]; then
	echo "$response" | jq -r '.' || printf "%s\n" "$response"
	exit 0
else
	echo "$response_body" \
	| jq -c 'if type == "object" then . else {raw: .} end' 2>/dev/null \
	| jq -s '{status: "http_error", code: $code, response: .[0]}' \
		--arg code "$http_code" \
		>&2
	exit 1
fi

An exit code of 0 indicates success. Any other exit code indicates failure. To aid troubleshooting, you can write error details to standard error (stderr) in the script. For example, the following snippet shows how to output error details and set the exit code to 1 when a curl request fails.

if ! http_code=$(curl -s -w "%{http_code}" \
	-H "Content-Type: application/json" \
	-d "$JSON_DATA" \
	-o "$temp_file" \
	-X POST "$URL"/"$REQUEST_PATH"); then
	echo "{\"status\": \"curl_error\", \"code\": $curl_exit_code}" \
	| jq . >&2
	exit 1
fi

Invoke code

Execute instruction

If the exit code is not 0, the instruction fails and is not re-executed. The system then returns an error.