Function Compute:Basics

Handlers

To configure the handler for your function, specify the Handler parameter within the Function Compute console. For more information, see Create a function.

Lifecycle hooks for function instances

In on-demand mode, instances are automatically created as needed. When they are not processing requests, on-demand instances are frozen. They will be destroyed if they remain in this frozen state for a certain period of time. You can configure lifecycle hooks for instances to perform callback operations when the instance status changes. The following lifecycle hooks can be configured in Function Compute: Initializer, PreFreeze, and PreStop. For more information, see Function instance lifecycle.

Initializer hook

An Initializer hook is invoked after an instance is initialized, but before the handler is executed. Function Compute ensures that the Initializer hook is executed only once throughout an instance's lifecycle. If the execution fails, the current instance is destroyed, and a new one is created to retry the execution.

You can incorporate time-consuming service logic into the Initializer hook. Doing so eliminates the need to run such service logic every time the function is called, thereby decreasing the function's latency. Examples of time-consuming service logic include creating connection pools, loading function dependencies, and performing other database-related tasks.

PreFreeze hook

A PreFreeze hook is executed before a function instance is frozen. You can use this hook to perform necessary operations before the instance is frozen, such as waiting for metrics to be successfully sent.

PreStop hook

A PreStop hook is executed before a function instance is destroyed. You can utilize this hook to carry out specific tasks prior to an instance's destruction. For example, you can configure a PreStop hook to ensure that database connections are closed and the status is reported and updated before the instance is destroyed.

Log management

Function Compute is integrated with Simple Log Service to store function invocation logs and logs that are printed in the function code to the Logstore. You can use the logging statements provided by Function Compute to record function logs, which facilitates debugging and troubleshooting. The following table describes the built-in log printing statements of different programming languages, along with the logging statements provided by Function Compute.

Both the logs printed by using the programming languages' built-in log printing statements and the logging statements provided by Function Compute are collected and stored in the Logstore. The latter logs are tagged with request IDs for easier filtering.

# Log printed by using the built-in log printing statement of the programming language
# print('hello world')
message:  hello world

# Log printed by using the logging statements provided by Function Compute
# logger.info('hello world')
message:  2020-03-13T04:06:49.099Z f84a9f4f-2dfb-41b0-9d6c-1682a2f3a650 [INFO] hello world
            

Log elements

A function execution log contains the service name, function name, current version, alias, and code logs.

The following example shows the data structure of a function execution log:

__source__:  
__tag__:__receive_time__:  1584072413
__topic__:  myService
functionName:  myFunction
message:  2020-03-13T04:06:49.099Z f84a9f4f-2dfb-41b0-9d6c-1682a2f3a650 [INFO] hello world
qualifier:  LATEST
serviceName:  myService
versionId:         

• The system prints FC Invoke Start RequestId: f84a9f4f-2dfb-41b0-9d6c-1682a2f3a650 when the function execution starts.

• The system prints FC Invoke End RequestId: f84a9f4f-2dfb-41b0-9d6c-1682a2f3a650 when the function execution ends.

Error handling

There are two types of errors in Function Compute: HandledInvocationError and UnhandledInvocationError.

• HandledInvocationError

  Only the errors returned by the callback parameter in Node.js are of the HandledInvocationError type. Error information is contained in the response.

  'use strict';
    module.exports.handler = function(event, context, callback) {
      console.log('hello world');
      callback('this is error', 'hello world');
    }          

  The following is an example of the error message:

  {"errorMessage":"this is error"}          

• UnhandledInvocationError

  All errors, except those classified as HandledInvocationError errors, fall under the UnhandledInvocationError category.

  The stackTrace property of an UnhandledInvocationError error is printed in logs. You can view the logs to find the corresponding stackTrace based on the context.

Operating system environment

Function Compute uses Debian 9 LTS for execution, and only the x86_64 architecture is supported.

You can modify the operating system environment by configuring layers or environment variables. For example, you can configure environment variables to change the time zone. By default, function instances run in UTC. If you set the value of the environment variable TZ to Asia/Shanghai, Function Compute changes its time zone to UTC+8. For more information, see Manage layers and Environment variables.