Adding Determinism and Safety to Uber IAM Policy Changes

What this post added

This post introduces a Policy Simulator tool designed to enhance the safety and determinism of IAM policy changes. It addresses the high stakes of policy modifications by enabling authors to preview the impact of their proposed changes in real-time, preventing accidental outages. The post details the architecture and two-stage process of the simulator, which involves fetching access logs and replaying them on reference and proposed policy sets to identify differences in access control results. It also highlights optimizations made to the log ingestion pipeline for low-latency fetching.