This talk describes the journey of building a brand new, platform-first, microservices architecture at Box. Building a new architectural stack presents a bunch of challenges with design choices, technology selection, and balancing simplicity with richness of feature offerings. A ‘steel thread’ to designing architectures helps identify the critical components of the stack and then gradually roll out incremental features - all while the engine is still running. The challenges really snowball when you on-board live traffic with high scale, high throughput and low latency requirements. The talk aims to share a structure on how to approach building large scale microservices architectures, challenges faced while on-boarding live traffic and finally lessons learnt while doing it.