A trigger is a method that is used to trigger function execution. In an event-driven computing model, an event source is an event producer, and a function is an event processor. Triggers are used to manage different event sources in a centralized manner. When an event that matches the rules defined for a trigger occurs, the event source invokes the function that is associated with the trigger.
What is a trigger?
Function Compute provides a computing model in which function execution is driven by events. The execution of a function can be triggered in the Function Compute console or by using SDKs or event sources. You can create triggers for a function. A trigger contains a set of rules. When an event that meets the rules occurs, the event source triggers the associated function.
If you need to use a trigger to trigger multiple functions, you can use Function Compute together with CloudFlow. For example, you can invoke a function by a trigger to start a CloudFlow process, in which multiple functions can be invoked. For more information, see the GitHub example.
Sample scenarios
Example 1: Trigger a function when the status of images stored in Object Storage Service (OSS) changes
An application stores images in OSS. You can invoke a function to download the images for processing and store the processed images in OSS or other services. If OSS can automatically detect newly uploaded images and invoke the associated functions, you do not have to manually invoke the functions. This helps simplify code development and resource usage. OSS event triggers can automatically detect the images and invoke functions in Function Compute. After the trigger is configured, the associated function is triggered to download and process images when new images are uploaded.
Example 2: Trigger function execution when logs in Simple Log Service are updated
An application uses Simple Log Service to collect updated logs at regular intervals. You can invoke functions to query and analyze incremental logs. If Simple Log Service can automatically detect updated logs and invoke the associated functions, you do not need to manually invoke the functions. Simple Log Service triggers can automatically detect such events and invoke functions in Function Compute. After you configure a Simple Log Service trigger, the associated functions are triggered when logs are updated to automatically consume incremental logs.
Scenario 3: Trigger function execution at specified intervals
An application needs to collect data every other hour. You can invoke a function every other hour to collect and process data. If the function in the Function Compute can be automatically executed every other hour, you do not need to manually invoke the function. In this case, you can configure a time trigger to detect time events and invoke the function in Function Compute. After you configure a time trigger, the functions are triggered to automatically collect and process data at specified time points.
Trigger types
Function Compute supports the following types of triggers based on how triggers are integrated:
Two-way integrated triggers: triggers that can be configured in Function Compute and event sources.
One-way integrated triggers: triggers that can be configured only in event sources.
Event triggers for Alibaba Cloud services: Triggers that can be configured in Function Compute and EventBridge. You do not need to configure the triggers in event sources.
Triggers can be classified into synchronous invocation triggers and asynchronous invocation triggers based on how functions are invoked. The following items describe the differences between the invocation methods. For more information, see Synchronous invocations.
Synchronous invocations: Results are returned after events are processed by a function. For example, a function invocation initiated in the Function Compute console is a synchronous invocation.
Asynchronous invocations: Results are returned after the events are written to the internal queues of Function Compute. Function Compute ensures that the messages are processed in a reliable manner.
Two-way integrated triggers
Trigger name | Invocation method | References | |
Time trigger | Asynchronous invocation | ||
OSS trigger | Asynchronous invocation | ||
Simple Log Service trigger | Synchronous invocation | ||
CDN trigger | Synchronous invocation | ||
Tablestore trigger | Synchronous invocation | ||
Self-managed Apache RocketMQ trigger | Synchronous or asynchronous invocation | ||
Simple Message Queue (formerly MNS) topic trigger | Asynchronous invocation | ||
HTTP trigger | Synchronous or asynchronous invocation | ||
EventBridge-based triggers | Simple Message Queue (formerly MNS) queue trigger | Synchronous or asynchronous invocation | |
ApsaraMQ for RocketMQ trigger | Synchronous or asynchronous invocation | ||
ApsaraMQ for RabbitMQ trigger | Synchronous or asynchronous invocation | ||
ApsaraMQ for Kafka trigger | Synchronous or asynchronous invocation | ||
ApsaraMQ for MQTT trigger | Synchronous or asynchronous invocation | ||
Data Transmission Service (DTS) trigger | Synchronous or asynchronous invocation | ||
One-way integrated triggers
For one-way integrated triggers, you must configure the triggers in event sources.
Trigger name | Invocation method | Reference |
API Gateway trigger | Synchronous or asynchronous invocation | |
Application Load Balancer (ALB) trigger | Synchronous or asynchronous invocation | |
DataHub one-way trigger | Synchronous or asynchronous invocation | |
IoT Platform trigger | Asynchronous | |
DataWorks trigger | Synchronous or asynchronous invocation | |
CloudFlow | Synchronous or asynchronous invocation |
Event triggers for Alibaba Cloud services
Trigger name | Invocation method | Reference |
Alibaba Cloud event source trigger | Synchronous or asynchronous invocation |