Understanding Lambda function invocation methods

After you deploy your Lambda function, you can invoke it in several ways:

• The Lambda console – Use the Lambda console to quickly create a test event to invoke your function.

• The AWS SDK – Use the AWS SDK to programmatically invoke your function.

• The Invoke API – Use the Lambda Invoke API to directly invoke your function.

• The AWS Command Line Interface (AWS CLI) – Use the aws lambda invoke AWS CLI command to directly invoke your function from the command line.

• A function URL HTTP(S) endpoint – Use function URLs to create a dedicated HTTP(S) endpoint that you can use to invoke your function.

All of these methods are direct ways to invoke your function. In Lambda, a common use case is to invoke your function based on an event that occurs elsewhere in your application. Some services can invoke a Lambda function with each new event. This is called a trigger. For stream and queue-based services, Lambda invokes the function with batches of records. This is called an event source mapping.

When you invoke a function, you can choose to invoke it synchronously or asynchronously. With synchronous invocation, you wait for the function to process the event and return a response. With asynchronous invocation, Lambda queues the event for processing and returns a response immediately. The InvocationType request parameter in the Invoke API determines how Lambda invokes your function. A value of RequestResponse indicates synchronous invocation, and a value of Event indicates asynchronous invocation.

If the function invocation results in an error, for synchronous invocations, view the error message in the response and retry the invocation manually. For asynchronous invocations, Lambda handles retries automatically and can send invocation records to a destination.