Synchronous invocation is a way to invoke a function. When you invoke a function synchronously, the event will directly trigger the function, and the Function Compute will run the function and wait for a response. when the function after the call is completed, the Function Compute will execution result directly to the such as return results, both the executive summary and the log output This topic describes the scenarios and limits of synchronous calls.


A synchronous call is a function that directly returns a result after an event is processed by a function. The scenarios for synchronous calls are extensive, including but not limited to the following scenarios:
  • You must view the execution results in a timely manner.
  • The function with the HTTP trigger set.


Resource call limit: The default maximum number of pay-as-you-go instances for your Alibaba Cloud account (master account) in a single region is 300.

Note You can use the function to Cloud Monitor console. To increase this limit, submit a ticket.

Execution concurrency

Execution concurrency is the number of concurrent invocations of a function in a specified period of time. You can use the following formula to estimate the execution concurrency:

Execution concurrency = Request rate × Function execution duration
  • Request Rate: the rate at which the function is called, that is, the number of requests per second or the number of events per second.
  • Function Execution Time: the duration between when the function request arrives at the start of the instance and when the request is executed. Unit: seconds.
For example, you have a function that processes OSS events. The average execution duration for the function is 3 seconds, and 10 OSS events are generated per second. You can use the formula to calculate that the execution concurrency for your function is 30.
Note The number of concurrent function executions affects your billing. For more information about billing, see Billing.