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IAM Policy Simulation and Safety

IAM Policy Simulation and Safety

1
posts
2025

Uber has developed a Policy Simulator to enhance the safety and determinism of IAM policy changes. This system allows policy authors to preview the impact of proposed changes in real-time by replaying access logs against both the current and proposed policy sets. This helps prevent accidental outages caused by misconfigurations, particularly with grant removals or unintended privilege escalations. The simulator fetches access logs from various Policy Enforcement Points (PEPs), optimizes their ingestion into Apache Pinot for low-latency access, and then replays them on local authorization engines to compare outcomes. This ensures that policy changes are thoroughly validated before deployment, significantly reducing the risk of production incidents.

2025

Adding Determinism and Safety to Uber IAM Policy Changes

9/18/2025

This post introduces the Policy Simulator, a new system designed to enhance the safety of IAM policy changes at Uber. It details the architecture, which involves fetching access logs from PEPs, optimizing their ingestion into Apache Pinot for low-latency access, and replaying them on two authorization engines (reference and proposed) to compare access control results. The post also outlines optimizations for log ingestion, such as prioritizing key data (actor, action, resource), focusing on distinct occurrences, and excluding irrelevant data. It explains how the simulator helps prevent outages by providing real-time impact analysis before policy deployment.