Reliability lessons from the 2025 AWS DynamoDB outage

The AWS DynamoDB outage in October 2025 highlighted the critical importance of understanding and preparing for service dependencies in cloud-based systems. The outage began with a DNS issue affecting DynamoDB in the US-EAST-1 region, leading to a prolonged EC2 outage and affecting major companies like Snapchat and Amazon. This incident underscores the inevitability of infrastructure failures despite robust maintenance efforts and the necessity for businesses to ensure their applications remain reliable during such disruptions. Companies are encouraged to map and test their service dependencies, distinguishing between critical and non-critical ones, and to establish redundancy plans to mitigate the impact of outages. Tools like Gremlin can simulate dependency failures and test redundancy, providing crucial insights into system resilience and helping teams prepare for potential outages. By understanding dependencies and testing infrastructure, organizations can better manage risks and avoid being caught off guard during future outages.