Showcase: Media Downloader

A production serverless media download service built on Mantle. Users submit YouTube URLs via an iOS app, the service downloads and processes the media asynchronously, then delivers it via CloudFront for offline playback. Originally built as a standalone CloudFormation/DynamoDB app, it is now the most feature-rich Mantle instance after a complete framework migration.

Architecture

iOS App
  │
  ▼
CloudFront ──► API Gateway (custom authorizer)
                    │
                    ├──► api/user/*      (register, login, logout, refresh, subscribe, delete)
                    ├──► api/device/*    (register, event)
                    ├──► api/files/*     (list files)
                    └──► api/feedly/*    (webhook, query auth)

                    │  (on download request)
                    ▼
               EventBridge (MediaDownloader bus)
                    │
                    ├──► SQS DownloadQueue ──► StartFileUpload Lambda
                    │                              │ (yt-dlp + ffmpeg layers)
                    │                              ▼
                    │                           S3 (files bucket)
                    │                              │
                    │                              ▼
                    │                        S3ObjectCreated Lambda
                    │                              │
                    │                              ▼
                    │                        SQS SendPushNotification ──► SNS ──► APNS (iOS)
                    │
                    └──► Scheduled: CleanupExpiredRecords, PruneDevices

                    Aurora DSQL (PostgreSQL-compatible, serverless)
                    ◄── All Lambdas (Drizzle ORM, IAM auth)

                    standalone: ApiGatewayAuthorizer, MigrateDSQL

Mantle Features Used

Feature	How it is used
defineApiHandler	All 13 API routes — auth, schema validation, OpenAPI metadata
defineEventBridgeHandler	StartFileUpload triggered by DownloadRequested event
defineScheduledHandler	CleanupExpiredRecords, PruneDevices on CloudWatch schedules
mantle build	Single command bundles all 18 handlers with esbuild
mantle deploy --stage	OpenTofu plan + apply across staging and production
mantle generate permissions	Auto-generates DSQL IAM grants from @RequiresTable decorators
exportToS3 / emitEvent	S3 export + EventBridge follow-up events from @mantleframework/aws
getDrizzleClient	Aurora DSQL with Drizzle ORM for all entity access
@mantleframework/auth	Better Auth sessions, OAuth accounts, Sign In With Apple
@mantleframework/observability	Structured logging, EMF metrics, X-Ray tracing (ADOT)

Key Numbers

• 18 Lambda handlers across 5 trigger types (API, SQS, S3, Scheduled, Standalone)
• 5 entity types: User, File, Device, Session, Account (+ 3 join tables)
• 4 Lambda layers: yt-dlp, bgutil, QuickJS, ffmpeg (all x86_64)
• 2 SQS queues: DownloadQueue (15 min visibility), SendPushNotification
• 2 SNS topics: push notifications, operations alerts
• 12 ADRs documenting architecture decisions

Repo

aws-cloudformation-media-downloader/ — symlinked at the monorepo root.