Function Compute:Instance lifecycle hooks

Usage notes

Instance lifecycle hooks are billed in the same way as standard invocation requests. However, their execution logs can only be viewed in Real-time Logs, Function Logs, or Advanced Logs. Hook logs are not displayed in the Invocation Request List. For more information, see View instance lifecycle hook logs.

Initializer hook

The initializer hook runs after a function instance starts but before the request handler runs. Function Compute ensures that an Initializer hook is successfully executed only once during the instance lifetime. If an Initializer hook fails on its first execution, the function invocation also fails. For the next invocation, a new function instance is created to execute the initializer hook.

The Initializer hook has only one context input parameter. The following sample code shows a simple Initializer hook.

export const initialize = async (context) => {
  console.log('initializer');
  return "";
}

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

initialize is the name of the Initializer hook. This name must match the value that you configure for the Initializer Hook in the Function Compute console. For example, if you set the Initializer Hook for a function to index.initialize, Function Compute loads the initialize method from the index.js file.

Method signature

• The only input parameter is context, which provides your FC function with its runtime context during invocation.

• The hook does not return a value. You must call `return` or `callback` in your code to end the function execution.

PreStop hook

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

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

export const preStop = async (context) => {
  console.log('preStop');
  return "";
}

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

Configure lifecycle hooks

Configure using the console

edition: 3.0.0
name: hello-world-app
access: default         # The alias of the key.

resources:
  hello_world:
    component: fc3 # The name of the component. Serverless Devs itself is like a game console and does not have specific business capabilities. Components are like game cartridges. You insert different cartridges into the console to get different features. Similarly, you use different components to implement different business capabilities.
    # actions:       # Custom execution logic. For more information about actions, see: https://docs.serverless-devs.com/serverless-devs/yaml#%E8%A1%8C%E4%B8%BA%E6%8F%8F%E8%BF%B0actions
    props:
      region: cn-hangzhou # For more information about how to use variables, see: https://docs.serverless-devs.com/serverless-devs/yaml#%E5%8F%98%E9%87%8F%E8%B5%8B%E5%80%BC
      functionName: nodejs-fc-hooks
      description: "Node.js lifecycle hooks by serverless devs"
      runtime: nodejs20
      code: ./code
      handler: index.handler
      memorySize: 128
      timeout: 30
      instanceLifecycleConfig:
        preStop:
          handler: index.preStop
          timeout: 3
        initializer:
          handler: index.initialize
          timeout: 3
      internetAccess: true
      logConfig: auto

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:

   2023-09-06 11:18:10FC Initialize Start RequestId: 1-64f7ef72-64caf1ff0046194d9a26bbd7
   2023-09-06 11:18:10load code for handler:index.initialize
   2023-09-06 11:18:102023-09-06 11:18:10 1-64f7ef72-64caf1ff0046194d9a26bbd7 [verbose] initializer
   2023-09-06 11:18:10FC Initialize End RequestId: 1-64f7ef72-64caf1ff0046194d9a26bbd7
   2023-09-06 11:18:10FC Invoke Start RequestId: 1-64f7ef72-64caf1ff0046194d9a26bbd7
   2023-09-06 11:18:10load code for handler:index.handler
   2023-09-06 11:18:10FC Invoke End RequestId: 1-64f7ef72-64caf1ff0046194d9a26bbd7

   Each function instance is cached for a period of time and not destroyed immediately, you cannot view the logs for PreStop hooks right away. To quickly trigger the 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:

   2023-09-06 11:08:10FC PreStop Start RequestId: 944bca62-b209-47a1-9e48-2723647bce0a
   2023-09-06 11:08:10load code for handler:index.preStop
   2023-09-06 11:08:102023-09-06 11:08:10 944bca62-b209-47a1-9e48-2723647bce0a [verbose] preStop
   2023-09-06 11:08:10FC PreStop End RequestId: 944bca62-b209-47a1-9e48-2723647bce0a

Sample program

Function Compute provides a sample MySQL program that uses Initializer and PreStop hooks. In this example, the Initializer hook retrieves MySQL database configurations from environment variables, creates MySQL connections, and tests connectivity. The PreStop hook closes the MySQL connections.

For more information, see nodejs14-mysql.

References

For more information about instance lifecycle hooks, see Configure instance lifecycles.