Function Compute:Basics

Built-in runtimes

Handlers in built-in runtimes follow a standard format. They process events from trigger sources such as Object Storage Service (OSS), Simple Log Service, ApsaraMQ for RocketMQ, and EventBridge triggers. You can set up an HTTP trigger for a function, which provides a Uniform Resource Identifier (URI) endpoint for direct HTTP invocation.

Custom and Custom Container runtimes

Handlers in custom runtimes or Custom Container runtimes differ from built-in runtimes. For details, see Web functions.

Configure the handler

Set the Handler parameter in the Function Compute console. For more information, see Create a function.

Initializer hook

The Initializer hook runs after an instance starts but before the handler runs. Function Compute guarantees the Initializer hook runs only once per instance and must complete successfully. If it fails, the behavior depends on the invocation type:

• Synchronous invocations -- the system returns the error.

• Asynchronous invocations -- the system retries based on the configured retry policy.

Place time-consuming initialization logic in the Initializer hook to avoid repeating it on every invocation. Common examples:

• Creating connection pools

• Loading function dependencies

• Database-related setup tasks

PreStop hook

The PreStop hook runs before a function instance is destroyed. Use it for cleanup tasks such as:

• Closing database connections

• Reporting and updating the instance's status

Logging statements

Each supported language has a built-in log statement and a Function Compute log statement. Function Compute log statements tag each entry with a request ID, which makes filtering easier.

Both types of statements send logs to the Logstore. The difference is that Function Compute statements tag each log entry with a request ID:

# Built-in statement: print('hello world')
message:  hello world

# Function Compute statement: logger.info('hello world')
message:  2020-03-13T04:06:49.099Z f84a9f4f-2dfb-41b0-9d6c-1682a2f3a650 [INFO] hello world

Log structure

A function execution log contains the service name, function name, current version, alias, and code logs. The following example shows the data structure:

__source__:
__tag__:__receive_time__:  1584072413
__topic__:  FCLogs:myFunction
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 the following markers at the start and end of each function execution:

• Start: FC Invoke Start RequestId: f84a9f4f-2dfb-41b0-9d6c-1682a2f3a650

• End: FC Invoke End RequestId: f84a9f4f-2dfb-41b0-9d6c-1682a2f3a650