Instacart's engineering team describes how they built a scalable multi-tenant marketing platform to support 350+ white-label retailers on Storefront Pro. The architecture provisions isolated third-party vendor workspaces per retailer, uses a stream consumer with batching (up to 50 users per call) to improve throughput, and routes messages through a Rails/Sidekiq-based CRM Service. Key challenges solved include cross-retailer data isolation, API rate-limit management, IP warming automation, and self-service template customization via a React UI with Liquid templates deployed through CI/CD. The platform achieves 99.9% delivery success and enables retailers to launch campaigns without engineering involvement. Future plans include adaptive campaign optimization and AI-assisted content generation.
