How to calculate the response time of an application end to end

Calculating end-to-end response time for your application can be achieved by using AWS X-Ray. AWS X-Ray helps you analyze and debug your distributed applications, such as those built using a microservices architecture. By providing insights into how your application is performing and where bottlenecks are occurring, you can identify the underlying causes of performance issues or errors.

1. Enable AWS X-Ray: First, you'll need to enable AWS X-Ray for your Lambda function. This can be done in the AWS Lambda console by enabling active tracing.

2. Instrument SDKs: If your application involves API calls or SDK calls to other AWS services, you'll need to instrument your code with the AWS X-Ray SDK. This SDK provides hooks into the command objects that the AWS SDKs use to make HTTP requests, allowing X-Ray to measure the latency of these requests.

3. Analyze X-Ray Trace: Once X-Ray is enabled and your application is instrumented, you can use the X-Ray console to analyze the traces. Traces provide a timeline view of the individual services and resources involved in processing your application's requests and their contribution to the overall end-to-end latency.

Remember, the network latency in a serverless architecture involves multiple components (client to API Gateway, API Gateway to Lambda, Lambda to S3, and then back again), each of which adds to the overall end-to-end latency. AWS X-Ray helps you measure and visualize these latencies in a trace map so you can analyze and troubleshoot them.

Remember to consider other elements that might affect response times, such as cold start times for your Lambda functions. Lambda functions that have not been invoked recently may take longer to respond the first time they're called. If your application requires consistently low response times, you might need to periodically invoke your functions to keep them warm.