AWS US EAST 1 Outage cascade analysis.pdf

When AWS sneezes, the internet catches a cold.
This week’s outage was a wake-up call — a reminder that even the most reliable cloud isn’t immune to fragility.

The Domino Effect:
A single DNS glitch cascaded through AWS’s control planes — disrupting identity, orchestration, and countless dependent services.
It wasn’t a hack. It wasn’t an insider.
It was the invisible backbone — #DNS and #BGP — showing just how much power two protocols quietly hold.

📊 Impact Metrics (CISO Takeaway):
• Uptime SLAs dropped below 80% in affected regions
• API latency spiked up to 1200%
• Failover orchestration lagged across multi-zone apps

⚙️ Lessons for CISOs & Cloud Architects:
• Build route-monitoring feeds for BGP
• Deploy redundant resolvers / private DNS caches
• Enable cross-region failover for control planes
• Test your blast radius containment regularly

1. AWS US-EAST-1 Outage
A 16-Hour Cascade Analysis
Timeline and Mitigation
On a OCT 2025, AWS's flagship US-EAST-1 region experienced a catastrophic failure
that rippled across the global cloud infrastructure for over 16 hours. What began as a
DNS resolution failure at 11:49 PM PDT cascaded through multiple service layers,
exposing fundamental vulnerabilities in even the most resilient cloud architectures.
This analysis dissects the incident timeline, root causes, and strategic implications
for enterprise cloud resilience planning.
Prepared By : Prabh Nair

2. Phase 1: The DNS
T
rigger Event
Timeline
1
1:49 PM 3 2:24 AM
P
DT
Duration: 2 hours 35
minutes
S
everity: Critical
Roo
t Cause
DNS resolution failed for DynamoDB
endpoints in US-EAST- 1, triggering a
chain reaction across dependent
services. Services relying on
DynamoDB4 including IAM, Lambda,
EC2 metadata services, and global
tables4began experiencing
widespread errors and timeouts.
DynamoDB Impact
Primary endpoint resolution failur
e
IAM Degradation
Service-to-service auth
entication failures
Lambda Disruption
Execution timeouts and errors
The DNS
failure exposed a critical vulnerability: even
distributed services become fragile when fundamental
infrastructure components fail. IAM's partial degradation
meant that service-to-service authentication became
intermittent, creating unpredictable failure patterns that were
difficult to diagnose and mitigate in real-time.

3. Phase 2: The EC2 Cascade
12:24 AM PDT
DNS resolution restored, but EC2
instance-launch subsystem fails to
recover due to corrupted DynamoDB state
2 3:00 AM PDT
EC2 instance launches fail region-wide,
cascading to ECS, RDS, Glue, and Redshift
services
35:30 AM PDT
Network Load Balancer health checks
degrade, creating connectivity failures
across Lambda, SQS, and CloudWatch 4 7:00 AM PDT
AWS implements throttling on EC2
launches and Lambda event polling to
contain blast radius
Extended Impact Window
The cascade phase lasted approximately 7
hours,
with degradation spreading to services that had no
direct DNS dependencies. This demonstrated how
tightly coupled AWS's internal architecture truly is.

4. The Dependency Chain Explained
DynamoDB DNS Failure
Unab
le to resolve service endpoints
IAM Authentication IssuesIdentity v
erification becomes unreliable
EC2 Launch Subsystem Down
Cannot p
rovision new infrastructure
NLB Health Checks FailLoad b
alancers lose traffic routing capability
Widespread Service DegradationLamb
da, SQS, CloudWatch experience connectivity loss
Critical Insight: Each la
yer in this dependency chain amplified the failure, demonstrating that
"high availability" architectures are only as resilient as their deepest dependency. The failure
progressed from DNS ³ Identity ³ Compute ³ Network ³ Application layers in a predictable
but devastating sequence.

5. Phase 3: Partial Containment
Recovery Window
9:38 AM 3 12:00 PM PDT
Duration: ~2.5 hours
AWS engineers restored Network Load Balancer health checks by
9:38 AM, immediately improving service connectivity across the
region. Lambda invocation errors dropped sharply as network paths
stabilized. However, EC2 launch throttles remained in place to
prevent overwhelming the recovering infrastructure.
75%
Lambda Recovery
Invocation error rate reduction
40%
EC2 Throttle Level
Remaining launch restrictions
85%
Service Stabilization
Overall availability improvement
Most services achieved functional stability during this phase, though performance remained degraded. The throttling strategy successfully prevented a secondary cascade, but created extended delays for customers attempting to scale infrastructure or deploy new resources. This conservative approach prioritized stability over speed.

6. Phase 4: Full Recovery & Backlog
Processing
01
12:00 PM PDT: EC2 Launch Restoration
Begins
Throttles gradually reduced across availability zones
02
2:48 PM PDT: Instance Launches
Normalized
All AZs returned to normal capacity provisioning
03
3:01 PM PDT: AWS Status Update
"All services operating normally" declared
04
3:53 PM PDT: Backlog Clearance
Complete
Redshift, Connect analytics, and Config queues fully
processed
Recovery vs. Resolution
A critical distinction emerged: while AWS declared
services "operational" at 3:01 PM, background
cleanup and backlog processing continued for
nearly an hour. This highlights the importance of
monitoring backlog drain time and latency
normalization, not just binary operational status.

7. Impact Metrics: By the Numbers
16h
Total Incident
Duration
From first DNS failure to
complete backlog
clearance
7h
Peak Cascade
Window
Period of active service
degradation and failures
12+
Affected Services
Including EC2, Lambda,

IAM, RDS, SQS,
CloudWatch, and more
3
Distinct Phases
Trigger, cascade, and
recovery with
overlapping impacts
DNS/DynamoDB
EC2 Compute
Network Services
Application Layer
Backlog Processing
0 5 10 15
The horizontal bar chart illustrates how different service categories experienced varying impact durations.
EC2 compute services bore the longest impact window, while the initial DNS trigger resolved relatively
quickly but set off a much longer cascade effect.

8. Strategic Takeaways for Security
Leaders
1
Dependency Depth Awareness
Even services marketed as "resilient" and "distributed" rely on regional DNS, IAM, and
DynamoDB. These become single points of failure when co-located in a single region. Map your
dependency chains beyond the obvious.
2
Cross-Region Control Planes
Implement cross-region architectures for critical control planes: identity services, logging
infrastructure, and telemetry systems. Your ability to observe and respond to incidents depends
on these remaining operational during regional failures.
3
Recovery Validation Protocols
"Operational" status does not equal "fully recovered." Monitor backlog drain times, latency
percentiles, and error rate normalization. Define clear thresholds for declaring actual recovery,
not just service restoration.
4
Tabletop DNS Failure Scenarios
Simulate DNS dependency failures in your environment. Test how IAM, container orchestration,
and monitoring systems behave when foundational DNS services become unavailable.
Document degradation patterns and recovery procedures.
5
SLA & Regional Risk Assessment
Review contractual SLAs for multi-AZ redundancy guarantees. Recognize that US-EAST-1
remains AWS's busiest and historically most failure-prone region. Consider workload
distribution strategies that account for regional risk profiles.

9. Building Resilience: Action Items
Immediate Actions
Audit all critical services for US-EAST-1
dependencies
Implement cross-region failover for identity and logging
Document DNS failure response procedures
Establish recovery validation metrics beyond binary status
Strategic Initiatives
Design chaos engineering tests for DNS failures
Develop multi-region control plane architecture
Create incident response playbooks for cascade scenarios
Negotiate enhanced SLA terms with cloud providers
CISO Priority: Schedule a DNS dependency failure tabletop exercise within the next 30 days. Use
this incident's timeline as your scenario template. Identify gaps in visibility, communication, and recovery capabilities before they become production incidents.
Assess Dependencies
Map all infrastructure and
service dependencies
Design Redundancy
Implement cross-region control
planes
Test Scenarios
Run tabletop and live failure
simulations
Monitor Continuously
Track recovery metrics and
backlog indicators
Iterate & Improve
Refine based on lessons
learned

10. Lessons from the Edge of Failure
The AWS US-EAST-1 outage serves as a stark reminder that cloud infrastructure resilience is not simply
purchased4it must be architected, tested, and continuously validated. The 16-hour cascade demonstrated
that even the world's most sophisticated cloud platform has single points of failure when foundational
services fail.
"The incident revealed that 'high availability' is a spectrum, not a binary state. Every architecture has
a breaking point4the question is whether you've identified yours before your customers do."
For CISOs and cloud architects, this incident underscores three non-negotiable principles: dependency awareness, cross-region redundancy, and recovery validation . The organizations that weathered this storm
most effectively had already mapped their dependency chains, implemented multi-region control planes, and defined clear recovery metrics beyond simple operational status.
The Path Forward
Transform this analysis into action. Use the
timeline as a scenario for chaos engineering. Test
your assumptions about failover capabilities.
Document what "recovered" actually means for
your critical systems. And most importantly,
recognize that in cloud infrastructure, resilience is
not a destination4it's a continuous practice of
preparation, testing, and refinement.