The holiday season is a time of joy, giving, and reflection — but in the world of system reliability, it’s also a time for critical system outages. This post marks the beginning of a special 10-day blog series leading up to Christmas Day. Each day, we’ll unwrap a new topic on Chaos Engineering, covering everything from real-world outages to practical techniques you can use to strengthen your systems.
Today, we’re kicking things off with a deep dive into some of the most notable outages in recent memory, exploring their root causes, and identifying how Chaos Engineering could have helped prevent them.
Think of it as the “Outages of Christmas Past, Present, and Future” — a festive look at how even the biggest names in tech can learn from failure. By the end, you’ll see why holiday resilience requires more than just eggnog and candy canes.
🎁 The Outages of Christmas Past: AWS (Amazon Web Services) Outage
The Incident
On December 7, 2021, AWS experienced a major outage that disrupted large swaths of the internet. Popular services like Disney+, Netflix, Slack, and Amazon’s own retail store were affected. The root cause? An internal network capacity issue within the AWS US-East-1 region. This network congestion caused connectivity failures between AWS’s internal services, impacting its critical APIs and application load balancers (ALBs).
Root Cause Analysis
- Root Cause: Internal network congestion leading to a capacity shortfall in a core AWS region.
- Impact: Major outages for services relying on AWS US-East-1, from e-commerce to streaming platforms.
- Duration: Approximately 7 hours.
How Chaos Engineering Could Have Helped
- Network Partition Experiments: Simulate network congestion to test system resilience.
- Failover Testing: Shift traffic to alternative AWS regions to ensure failover logic works.
- API Rate Limiting Simulations: Test for tight service-to-service dependencies that could cascade during congestion.
Lesson Learned
- Regional Isolation Matters: Build the ability to shift traffic between cloud regions quickly.
- Test for Regional Dependency: Services must avoid heavy reliance on a single region.
- Test Blast Radius Controls: Ensure system changes have limited impact on production.
🎄 The Outages of Christmas Present: Slack’s New Year’s Eve Outage
The Incident
On December 31, 2020, Slack experienced a widespread outage as teams across the globe prepared for New Year’s celebrations. Millions of users couldn’t send messages or access the platform. The issue persisted well into January 1, 2021.
Root Cause Analysis
- Root Cause: A sudden surge in usage led to performance issues in Slack’s backend responsible for real-time messaging.
- Impact: Slack’s web, mobile, and desktop clients were disrupted, preventing message delivery.
- Duration: Approximately 6-8 hours.
How Chaos Engineering Could Have Helped
- Traffic Spike Simulations: Simulate sudden surges in user activity to identify bottlenecks.
- Message Queue Failure Simulations: Identify how queue slowdowns affect message delivery.
- Horizontal Scaling Tests: Ensure scaling triggers can handle sudden user spikes.
Lesson Learned
- Scale for the Unexpected: Build more aggressive auto-scaling triggers.
- Backpressure Management: Design queues to buffer delayed messages, not drop them.
- Pre-Holiday Chaos Tests: Simulate usage surges before high-traffic events like New Year’s Eve.
🎅 The Outages of Christmas Future: Microsoft Teams Outage
The Incident
On February 3, 2021, Microsoft Teams experienced a global outage, leaving millions of workers stranded. The culprit? Expired authentication tokens. Microsoft failed to renew an internal TLS certificate, which caused system-wide authentication failures.
Root Cause Analysis
- Root Cause: Failure to renew an internal TLS certificate that authenticated user logins.
- Impact: Users worldwide couldn’t log in to Microsoft Teams.
- Duration: Around 4-5 hours.
How Chaos Engineering Could Have Helped
- Certificate Expiration Chaos Tests: Test system response to expiring certificates.
- Failover Authentication Tests: Implement fallback authentication flows for login failures.
- Alerting Chaos Tests: Ensure alerting systems notify teams before cert expiration.
Lesson Learned
- Don’t Let Certs Expire: Automate certificate renewal well before expiration.
- Run Authentication Failure Tests: Test how the system reacts when key authentication services fail.
- Create “Expired Certificate” Alerts: Ensure alerts fire in time to prevent expiry-related issues.
🛠️ How to Apply These Lessons to Your Own Systems
Outages don’t wait for a convenient time to strike — just ask AWS, Slack, or Microsoft. But with Chaos Engineering, you don’t have to wait for an actual outage to know how your system will respond. Here’s how you can prepare for the “Outages of Christmas Past, Present, and Future” in your own systems.
- Run “Outage of Christmas Past” Game Days: Simulate network partitions like the AWS outage to understand your regional dependencies.
- Recreate “Outage of Christmas Present” Spikes: Simulate traffic surges similar to Slack’s experience to see how your system holds up.
- Plan for “Outage of Christmas Future” Certificate Expiration: Schedule chaos experiments that force certificate expiration to reveal potential issues.
🎉 Your Turn: Share Your Outage Stories
Have you experienced a major outage at work? Did it feel like a Christmas Eve surprise? We want to hear from you! Drop your story in the comments and tell us how it happened, how you resolved it, and what lessons you’d share with others. The best stories may be featured in a future post!
Closing Thoughts
Outages don’t take holidays. They’re as unpredictable as holiday weather and as frustrating as tangled Christmas lights. But by using Chaos Engineering, you can prepare your systems to weather the storms, mitigate the damage, and keep the holiday cheer alive.
So this Christmas, as you sip your hot cocoa and gaze at the twinkling lights, think about the resilience of your own systems. Are they ready for “The Outages of Christmas Past, Present, and Future”? If not, it’s time to schedule your next Chaos Game Day.
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