If you couldn't order from Starbucks, watch Netflix, or even access your mobile banking on Monday, you weren't alone. A massive Amazon Web Services (AWS) outage crippled a large portion of the internet. Now, Amazon has released a postmortem assessment, and the cause was surprisingly small: a single bug.
In its technical breakdown, Amazon explained the outage began with a "race condition." This common but dangerous bug occurs when two automated programs try to update the exact same piece of data at the exact same time.
The result? Instead of a clean update, the process created a corrupted, empty entry in Amazon's DNS—which acts as the internet's "phonebook."
As Cisco’s ThousandEyes monitoring service explained, "That telephone book effectively went poof."
The Cascade Effect: How One Glitch Spiraled
This single empty DNS record set off a catastrophic chain reaction that took down Amazon's own core services.
DynamoDB Fails: The bug first broke AWS's DynamoDB, a massive and critical database service that many other AWS functions rely on.
Core Services Collapse: With DynamoDB down, other essential services that depend on it also failed. This included EC2 (the virtual servers that power countless apps) and the Network Load Balancer (which manages traffic).
The Internet Goes Down: Because major companies like Netflix, Starbucks, United Airlines, and thousands of others build their apps on EC2 and DynamoDB, their services went offline for millions of users.
The Recovery Problem
The recovery wasn't as simple as flipping a switch. According to Amazon, when the initial DynamoDB issue was fixed, all the failed EC2 servers tried to reboot and reconnect at the exact same time. This massive, simultaneous surge of traffic overwhelmed the system, causing further delays.
The Fix and Future Prevention
Amazon has apologized for the "significant impact" this event caused. The company stated it is implementing several changes to prevent a repeat, including:
Fixing the specific "race condition" bug so two programs can't conflict in this way again.
Adding a new, more robust testing suite for its EC2 service to handle recovery better.
While outages of this scale are rare, tech experts note that they are an inevitable reality of complex cloud systems. The key takeaway for the tech industry is not just that it happened, but how Amazon diagnosed it and is working to prevent it from happening again.