This topic describes how Node.js implements and applies the function instance lifecycle callback method.

Background information

After you implement and configure the function instance lifecycle callback, the Function Compute will call the corresponding callback program when the related instance lifecycle event occurs. Currently, Node.js run time supports initializer, PreFreeze, and PreStop function instance lifecycle callbacks. For more information, see Function instance lifecycle callback.

Initializer callback

Initialization callback (Initializer callback) is executed after the function instance is successfully started and before the request handler is run. The Function Compute ensures that the Initializer callback can be successfully executed at most once within an instance lifecycle. For example, after your Initializer callback fails the first execution, the system retries until it succeeds before executing your request handler.

The Initializer callback has only one context input parameter and uses the same method as the event request handler.

One of the simplest initializer callbacks is as follows. 

exports.initialize = function(context, callback) {
  console.log('initializer');
  callback(null, "");
};

The initialize is the name of the Initializer callback method. It must be the same as the Initializer callback program that you configured in the Function Compute console. For example, if the Initializer callback program that you configured for a function is index.initialize, the Function Compute will load the initialize method defined in the index.js after configuring the Initializer property.

Method signature

  • The input parameters are context only and provide the running context information for your FC function call when it is called.
  • Initializer functions return no values.

PreFreeze callback

The PreFreeze callback program is executed before the function instance is frozen. The method signature is the same as the Initializer callback.

One of the simplest PreFreeze programs is shown below. 

module.exports.preFreeze = function(context, callback) {
  console.log('preFreeze');
  callback(null, "");
};

PreStop callback

The pre-stop callback program (PreStop callback) is executed before the function instance is destroyed. The method signature is the same as the Initializer callback.

One of the simplest preStop programs is shown below. 

module.exports.preStop = function(context, callback){
  console.log('preStop');
  callback(null, "");
}

Configure the lifecycle callback function

Use the Function Compute console

You can configure the Initializer callback program, PreFreeze callback program, and PreStop callback program in the FC function configuration of the Function Compute console. For more information, see Function instance lifecycle. The callback format is [File name. Method name]. Example:
  • The Initializer callback program is set to index.initialize to indicate the initialize method in the index.py file.
  • The PreFreeze callback is set to index.preFreeze to indicate the preFreeze method in the index.py file.
  • The PreStop callback program is set to index.preStop, which indicates the preStop method in the index.py file.
db-node.js-lifecycle

Configure by using the Serverless Devs tool

If you use Serverless Devs, you must add Initializer callback, PreFreeze callback, and PreStop callback to the s.yaml configuration file.
  • Initializer callback configuration

    Add the initializer and initializationTimeout fields under function configuration.

  • PreFreeze callback configuration

    Add instanceLifecycleConfig.preFreeze fields under function configuration, including handler and timeout.

  • PreStop callback configuration

    Add instanceLifecycleConfig.preStop fields under function configuration, including handler and timeout.

The following shows an example. 

edition: 1.0.0          #  The version of the YAML syntax. The version complies with the semantic versioning specification.
name: hello-world # The name of the project.
access: default # Key alias

services:
  fc-deploy-test: # Module name
    component: devsapp/fc  # The name of the component.
    props: # Attribute values of components
      region: cn-hangzhou # Region
      service: # Service configuration
        name: the name of the fc-deploy-service# service.
        description: a short description of the dem component# Service
      function: # Function configuration
        name: the name of the fc-base-service# function.
        description: 'Short description of the this is test'# function
        codeUri: './code' # Code location
        handler: 'The entry for index.handler'# function execution. The specific format is related to the language.
        memorySize: 128 # The memory specifications of the function.
        runtime: nodejs14 # run time
        timeout: 60 # The timeout period of the function.
        initializationTimeout: 20 # The timeout period of the initialization method.
        initializer: index.initialize # The initialization method.
        instanceLifecycleConfig: # Extension function
          preFreeze: # The PreFreeze function
            handler: index.preFreeze # Function entry
            timeout: 60 # The timeout period.  
          preStop: # PreStop functions
            handler: index.preStop # Function entry
            timeout: 60 # The timeout period.

For more information about the YAML configuration specifications of Serverless Devs, see Basic features.

Sample programs

Function Compute provides a MySQL sample program that uses Initializer callback and PreStop callback. In this example, the Initializer callback function is used to obtain the MySQL database configuration from environment variables, create a MySQL connection, and test the connectivity. The PreStop callback function is responsible for closing the MySQL connection.

For more information, see nodejs14-mysql.