# Retail Custom AWS Build vs Buy — Decision Matrix (July 2026)

| Capability | Prefer **buy / SaaS** | Prefer **custom on AWS** |
| --- | --- | --- |
| Loyalty points at checkout | Standard tiers, low peak QPS | Sub-100ms + peak QPS the SaaS can’t hit |
| Pricing / promos | Simple % / BOGO | Nested rules, A/B, customer-specific, catalog-wide cache |
| Inventory sync | Single channel | Multi-channel + WMS + EventBridge/SQS fan-out |
| Image / asset delivery | Basic CDN | S3 + CloudFront (or multi-CDN) with catalog-keyed cache |
| Email at peak | ESP that already scales | SES + dedicated IPs when volume/reputation is the product |

## Engagement scoping (copy)

| System | Traffic shape | Latency SLO | Integration count | Build / buy |
| --- | --- | --- | --- | --- |
| | | | | |

## Anti-patterns

- Microservices rewrite before fixing CDN/image path
- Sync HTTP chains for order → inventory → email (use events)
- Single CDN with no origin protection before Black Friday