Synchronous and Asynchronous Invocations in AWS Lambda

AWS Lambda supports two primary invocation types: Synchronous and Asynchronous. Understanding these invocation methods is crucial for optimizing your Lambda functions for different scenarios.

What are Synchronous Invocations?

In a Synchronous Invocation, the caller waits for the Lambda function to complete execution and return a response. This type is best suited for use cases where the result of the function is immediately required.

Real-life Analogy:

Imagine ordering coffee at a café and waiting at the counter until the coffee is prepared. Only after receiving your coffee do you leave.

Example Code:

Here’s a sample Lambda function to demonstrate a synchronous invocation:

import time
import json

def lambda_handler(event, context):
    time.sleep(5)  # Simulates processing time
    print("Processing complete")
    return {
        "statusCode": 200,
        "body": json.dumps("Hello from Lambda!")
    }

Execution Flow:

The caller invokes the Lambda function.
The caller waits for the function to finish execution (e.g., 5 seconds in this case).
The function returns the result to the caller.

What are Asynchronous Invocations?

In an Asynchronous Invocation, the caller sends the request to Lambda and receives a response immediately without waiting for the function to complete execution. This method is ideal for background processing tasks.

Real-life Analogy:

Imagine ordering coffee at a café and returning to your table. The staff delivers the coffee to your table once it’s ready.

Key Differences:

The function execution runs independently.
The caller is not blocked while waiting for the function to finish.

Asynchronous Invocation via AWS CLI:

You can trigger a Lambda function asynchronously using the AWS CLI:

aws lambda invoke \
    --function-name yourLambdaFunctionName \
    --invocation-type Event \
    output.txt

--invocation-type Event: Specifies asynchronous invocation.
The response status will be 202 Accepted, indicating the request has been queued.

Synchronous vs. Asynchronous: Key Differences

Feature	Synchronous Invocation	Asynchronous Invocation
Response Time	Caller waits for the function to finish execution.	Caller receives immediate acknowledgment.
Use Cases	Real-time APIs, user-facing operations.	Background tasks, batch processing.
Invocation Type	Default when invoked from API Gateway or CLI without flags.	Use `--invocation-type Event` in CLI.
Response	Returns the function’s result.	Provides a status acknowledgment.

Monitoring Asynchronous Invocations

Asynchronous invocations are processed in the background. To monitor these executions:

Check the CloudWatch Logs for execution details.
Use the log_stream_name from the Lambda context object to trace the specific execution.

Common Use Cases

Synchronous Invocation:

APIs: Calling a database or fetching data from an external service.
Real-time operations: Requiring immediate user feedback.

Asynchronous Invocation:

S3 Trigger: Automatically generating thumbnails for uploaded images.
Event Processing: Processing logs, analytics, or notifications.

Summary

Synchronous Invocation: Caller waits for the function to complete, suitable for real-time needs.
Asynchronous Invocation: Caller queues the request and moves on, ideal for background tasks.
Choose the invocation type based on your application's requirements.

For more AWS tutorials, visit learning-ocean.com.

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