1. Problem Statement
This project addresses the inefficiencies and costs associated with repetitive voice synthesis from dynamic text input. By implementing an intelligent S3-based caching layer for Amazon Polly, the solution significantly improves performance, reduces operational costs, and provides a scalable foundation for web applications requiring on-demand voice generation.
- Implementing deterministic audio caching using hashed S3 keys
- Eliminating duplicate Amazon Polly charges
- Reducing audio retrieval latency with efficient S3 pre-signed URLs
- Providing real-time feedback and direct downloadable voice output to users
2. Architecture Overview
This serverless system converts text into lifelike speech, leveraging key AWS services for efficiency and scalability. A frontend interface on sedky.net allows users to input text and select a voice. This request is routed through API Gateway to an AWS Lambda function. The Lambda function intelligently checks for existing audio in an S3 cache. If found, it quickly returns a pre-signed URL for direct download. Otherwise, it invokes Amazon Polly to synthesize new speech, stores this new audio in S3, and then provides the pre-signed URL. Amazon SNS is used to publish notifications for newly generated audio files, and S3 lifecycle rules ensure cached files auto-expire after 7 days.
Overview of the serverless architecture for the Text-to-Speech converter.
3. Live Demo
Experience the converter firsthand. Enter your text, select a voice, and generate speech directly below or open in a new tab.
Interactive demo of the AWS Text-to-Speech converter.
4. Step-by-Step Implementation
Lambda execution role with permissions for Polly, S3, and SNS.
Execution role permissions summary view.
Trust policy for Lambda execution role.
Lambda function configuration summary.
Lambda function code handling audio synthesis and caching.
Successful Lambda invocation result.
API Gateway HTTP endpoint created for POST requests.
Successful API Gateway invocation returning pre-signed URL.
S3 bucket created for storing cached MP3 audio files.
5. Business Impact
- Prevents redundant Polly usage via deterministic caching
- Improves UX with fast audio load times
- Scales well for voice automation use cases (IVR, accessibility, podcasting)
6. Real-World Scenarios
This serverless application could support accessibility features in internal tools, multilingual support bots for customer service, or automated QA for localized audio playback during testing workflows.
7. Cost & Security Considerations
- Polly usage billed per character, optimized with caching
- S3 auto-expiration reduces storage cost
- Pre-signed URLs provide secure access, no public buckets used
- IAM roles scoped to minimum privileges
- No credentials hardcoded, all configurations passed via environment variables
- API Gateway secured with throttling and CORS headers
8. AWS Well-Architected Framework Alignment
| Pillar | Implementation Notes |
|---|---|
| Security | IAM scoped to least privilege, S3 private, pre-signed access only |
| Reliability | Handles Polly or S3 errors gracefully |
| Performance Efficiency | Cache-first design using pre-signed URLs |
| Cost Optimization | Avoids duplicate synthesis charges, auto-expiry cache |
| Operational Excellence | Monitored with SNS, CloudWatch, structured logging |
9. Challenges & Resolutions
- 403 Forbidden: Resolved with correct Lambda resource policies
- S3 access errors: IAM and trust relationship fixed for Lambda
- Audio decoding: Polly response stream handled as binary buffer
- Duplicate generation: Prevented with hash-based cache key