Function Compute:Configure instance lifecycles

Instance lifecycles

As shown in the preceding figure, the lifecycle of a Function Compute instance include the Create, Invoke, and Destroy phases.

• Create

  During this phase, Function Compute performs the following tasks in sequence:

  • Create an instance.

  • Initialize a runtime.

  • Execute an Init hook.

  If you use provisioned instances, Function Compute allocates function instances and performs the Create process immediately after you configure provisioned instances. Function invocations may not be initiated right away. Therefore, a long time interval may exist between the runtime initialization, Init hook running, and invocation phases.

  If you use on-demand instances, Function Compute immediately performs the Create process when requests are submitted. If an Init hook is configured for the function, the Invoke process is performed after the Init hook is executed.

  For a function instance, the Init hook configured for the function is executed only once. If the execution fails, another function instance is allocated to execute the Init process. The instance whose Init hook fails is destroyed.

• Invoke

  By default, instances that run in standard runtimes of Function Compute can execute only one request at a time. Instances that run in custom runtimes and Custom Container runtimes can execute multiple requests at a time. You can set the instance concurrency to a value greater than one to allow one instance to execute multiple requests at a time. For more information, see Configure instance concurrency.

• Destroy

  This phase is triggered if a function instance does not receive any invocations for a period of time. During this phase, Function Compute executes the PreStop hook first. You can perform cleanup tasks in PreStop hooks.

Instance freezing mechanism

Function Compute freezes an instance when no invocations are initiated for a period of time and unfreezes the instance when new requests are submitted. The following figure shows the process.

An instance is frozen in the following scenarios:

• The instance is initialized and no invocations are made yet.

• The instance is invoked to process requests and subsequent requests are not immediately submitted.

After invocations are complete, Function Compute freezes the function instances. In this case, the background processes, threads, and coroutines in the program cannot continue to run, and asynchronous logs may fail to write.

Limits

• All runtimes support the Init and PreStop hooks.

• The input parameter of a PreStop hook does not have the event parameter.

• PreStop hooks have no return values. The logic that is appended to a PreStop hook to return values does not take effect.

• If you use a Java runtime, you must update fc-java-core to 1.4.0 or later. Otherwise, you cannot use the PreStop hook.

• When a function returns responses, Function Compute freezes the function instance. You cannot assume that all asynchronous processes, threads, and coroutines are successfully executed when responses are returned. You cannot assume that asynchronous logs are refreshed either.

Prerequisites

A function is created. For more information, see Create an event function.

Configure lifecycle hooks

  codeUri: './code.zip'
  ......
  instanceLifecycleConfig:
    preStop:
      handler: index.PreStop
      timeout: 60

  codeUri: './code.zip'
  ......
  instanceLifecycleConfig:
    preStop:
      handler: ""
      timeout: 60

Query hook-related logs

After you configure an instance lifecycle hook and run the code of the hook, you can query the logs of the hook.

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 Logs tab. On the Invocation Requests tab, find the request whose logs you want to view and click Advanced Logs in the Actions column.

   You can use a copied instance ID to query the start and end logs of all lifecycle hooks. You can also use the instance ID together with a hook keyword to query the start and end logs of a specified hook, such as c-62833f38-20f1629801fa4bd***** and PreStop.

   You can also query the request logs based on the request ID in the start logs and the end logs. If the user log does not contain a request ID, you can click the icon to obtain the context log.

Billing rules

You are not charged for the number of invocations for instance lifecycle hooks. The billing of other billable items is the same those in the invocation phase. The following figure shows the billable phases.

For more information about billing, see Billing overview.