Why the Web was Down Today - Explained by a Retired Microsoft Engineer

About this video

• Video Title: Why the Web was Down Today - Explained by a Retired Microsoft Engineer
• Channel: Dave's Garage
• Speakers: Dave
• Duration: 16:32

Overview

This video explains the causes and implications of a widespread AWS outage that occurred on Monday, October 20th, 2025. The speaker, a retired Microsoft systems engineer, breaks down the technical details, including the role of DNS and US East 1 region failures, and discusses the broader implications for internet infrastructure and the need for greater resiliency.

Key takeaways

• AWS Outage Impact: A significant AWS outage, particularly affecting the US East 1 region, caused widespread internet disruptions, impacting various services like gaming platforms, financial apps, and even Amazon's own services like Alexa and Ring.
• Root Cause - DNS Failure: The primary cause of the outage was identified as a DNS resolution failure for the DynamoDB API endpoint in the US East 1 region. This seemingly small issue had a cascading effect due to the critical role DynamoDB plays in many applications for various functions.
• Cascading Failures and Retries: The DNS failure led to client SDKs retrying and hammering the service, turning an elastic load absorber into a source of failure. This highlights the fragility of complex, interconnected systems.
• Regional Dependency: Many applications are heavily dependent on specific AWS regions (like US East 1), which lack true multi-region active-active setups. This means a failure in one region can have global consequences if not properly architected for.
• Resiliency and Practicing Failures: True resiliency requires designing applications to be region-agnostic and actively practicing failure scenarios (chaos engineering) to identify and address weaknesses before they cause real-world outages.
• Monoculture Risk: The incident underscores the risk of internet monoculture, where reliance on a few major cloud providers creates single points of failure with significant global impact.
• DNS as a Critical Component: The video emphasizes the crucial role of DNS in the modern internet, acting as a fundamental "phone book" whose failure can cripple interconnected services.