Function Compute:Lifecycle hooks for function instances

Initializer hooks

An Initializer hook is invoked after a function instance is started and before a handler runs. Function Compute ensures that the Initializer hook is successfully invoked only once in the lifecycle of a function instance. If your Initializer hook fails to be executed, an error is returned for the function invocation. When you invoke the function next time, the system creates another function instance to execute the Initializer hook.

An Initializer hook contains only the context input parameter and can be invoked in the same manner as a handler.

The following sample code provides an example of a simple Initializer hook:

def initialize(context):
    print("initialize invoked")

In the preceding sample code, initialize is the name of the Initializer hook. The name must be the same as the Initializer hook that you configured in the Function Compute console. For example, if you set Initializer Hook to index.initialize for a function, Function Compute loads the initialize method defined in the index.py file after the Initializer property is configured.

Method signature

• The input parameter is only context, which provides your FC function with the running context during invocations.

• No value is returned.

PreStop hooks

A PreStop hook is executed before a function instance is destroyed. The method signature of a PreStop hook is the same as the method signature of an Initializer hook.

The following sample code provides an example of a simple PreStop hook:

def preStop(context):
    print("preStop invoked")

Configure lifecycle hooks

Use the Function Compute console

In the Function Compute console, you can configure the Initializer Hook and PreStop Hook parameters of a function. For more information, see Configure the instance lifecycle.

The format of a hook is [File name.Method name]. For example, if you set Initializer Hook to index.initialize, the initialize method in the index.py file is loaded.

edition: 3.0.0
name: fcDeployApp
access: "default"

vars: # The global variables
  region: "cn-hangzhou"

resources:
  hello_world:
    component: fc3 # The name of the component
    props:
      region: ${vars.region}              # For information about how to use variables, visit https://docs.serverless-devs.com/serverless-devs/yaml#%E5%8F%98%E9%87%8F%E8%B5%8B%E5%80%BC.
      functionName: "emojipy"
      description: 'this is emoji'
      runtime: "python3"
      code: ./
      handler: index.handler
      memorySize: 128
      timeout: 30
      environmentVariables:
        PYTHONPATH: /code:/code/python:/opt/python
initializationTimeout: 20                      # The timeout period for the execution of the initialization method.
#     initializer: index.my_initializer # The initialization method
      instanceLifecycleConfig:      # The extension function
        preStop:                                     # The PreStop hook
          handler: index.preStop    # The handler
          timeout: 60               # The timeout period
        initializer: # The Initializer hook
          handler: index.initialize
          timeout: 60  

View the logs of instance lifecycle hooks

You can view the logs for lifecycle hook in Logs.

1. Log on to the Function Compute console. In the left-side navigation pane, click Functions.

2. In the top navigation bar, select a region. On the Functions page, click the function that you want to manage.

3. On the function details page, click the Test Function tab, click Test Function, and then choose Logs > Function Logs.

   On the Logs tab, you can view function invocation logs and Initializer logs. Example:

   2024-03-04 17:57:28FC Initialize Start RequestId: 1-65e59b07-1520da26-bf73bbb91b69
   2024-03-04 17:57:282024-03-04 09:57:28.192 1-65e59b07-1520da26-bf73bbb91b69 [info] initializer
   2024-03-04 17:57:28FC Initialize End RequestId: 1-65e59b07-1520da26-bf73bbb91b69
   2024-03-04 17:57:28FC Invoke Start RequestId: 1-65e59b07-1520da26-bf73bbb91b69
   2024-03-04 17:57:28FC Invoke End RequestId: 1-65e59b07-1520da26-bf73bbb91b69

   Each function instance is cached for a period of time and not immediately destroyed, you cannot view logs for PreStop hooks right away. To quickly trigger a PreStop hook, you can update the function configurations or function code. After the update is complete, you can view the logs for PreStop hooks in Function Logs. The following sample code shows an example:

   2024-03-04 18:33:26FC PreStop Start RequestId: 93c93603-9fbe-4576-9458-193c8b213031
   2024-03-04 18:33:262024-03-04 10:33:26.077 93c93603-9fbe-4576-9458-193c8b213031 [info] preStop
   2024-03-04 18:33:26FC PreStop End RequestId: 93c93603-9fbe-4576-9458-193c8b213031

Sample program

Function Compute provides a sample MySQL program that uses Initializer and PreStop hooks. In this example, an Initializer hook is used to obtain MySQL database configurations from environment variables, create MySQL database connections, and test the connectivity. A PreStop hook is used to close MySQL connections.

For more information, see python3-mysql.