To decrease latency for a global user base, an edge-optimized API endpoint is the best choice. This endpoint type leverages the Amazon CloudFront content delivery network (CDN) to route requests to the nearest edge location, minimizing network latency. Enabling API caching serves frequently requested data from the cache at the edge, further reducing latency by avoiding calls to the backend Lambda function. Additionally, enabling content encoding compresses the API payload, which reduces the amount of data transferred over the network. This smaller payload size decreases transfer time, directly contributing to lower overall latency for the end-user.

B. A Regional API endpoint is not suitable for a global user base as it does not use the CloudFront CDN, leading to higher latency for users geographically distant from the deployment region.

C. Reserved concurrency for Lambda manages execution capacity and prevents throttling; it does not directly reduce network transfer latency, which is the primary concern for a global audience.

D. This option combines two suboptimal choices: a Regional endpoint, which increases network latency for global users, and reserved concurrency, which does not address the core issue of transfer latency.

1. AWS API Gateway Developer Guide

"Choosing an API endpoint type to set up": This document states

"An edge-optimized API endpoint is best for geographically distributed clients. API requests are routed to the nearest CloudFront Point of Presence (POP)." This supports the choice of an edge-optimized endpoint for a worldwide user base.

2. AWS API Gateway Developer Guide

"Enable payload compression for an API": This guide explains

"When a client enables compression

the client can receive the API's response with a compressed payload... This can reduce the size of the response payload

which can reduce the latency of your API." This validates the use of content encoding.

3. AWS API Gateway Developer Guide

"Enabling API caching to enhance responsiveness": This source details how caching works: "You can enable API caching in Amazon API Gateway to cache your endpoint's responses. With caching

you can reduce the number of calls made to your endpoint and also improve the latency of requests to your API."

4. AWS Lambda Developer Guide

"Configuring reserved concurrency": This document clarifies the purpose of reserved concurrency: "To guarantee that a specific function can scale to a certain number of concurrent executions without being throttled

you can configure reserved concurrency." This shows it's for performance and availability

not network latency reduction.