Post-Incident Analysis: AWS US-EAST-1

 

Post-Incident Analysis: AWS US-EAST-1 Outage (October 20, 2025)

1. Incident Overview and Scope of Impact

The major AWS service disruption on October 20, 2025, began late on the previous night and lasted for nearly 15 hours, causing widespread issues globally.

Key Detail	Description
Primary Region Affected	US-EAST-1 (N. Virginia). This region is critical, as many global AWS control plane services and management features rely on its endpoints.
Availability Zones Affected	Multiple Availability Zones (AZs) within US-EAST-1 experienced connectivity and provisioning issues.
Core Services Impacted	DynamoDB, AWS Lambda, Amazon EC2, Amazon CloudWatch, AWS Systems Manager, AWS Security Token Service (STS), and AWS Connect.
Global Effect	Due to dependencies on US-EAST-1 endpoints (such as IAM authentication and DynamoDB Global Tables), global applications and services worldwide experienced errors and downtime, including major banking, e-commerce, and gaming platforms.

2. Root Cause and Cascading Failure

AWS identified the event as a complex, cascading failure chain originating from internal systems within the US-EAST-1 region.

The Chain of Events

1. Initial Trigger (DNS Failure): The outage was initially triggered by a DNS resolution issue affecting the regional API endpoint for DynamoDB. This failure prevented dependent services and applications from locating the DynamoDB service.

2. EC2 Internal Impairment: After the initial DynamoDB DNS issue was resolved, the EC2 internal subsystem responsible for provisioning and launching new virtual machines became impaired. This was due to its reliance on DynamoDB for essential metadata retrieval, preventing new EC2 instances (and services like ECS/Fargate that rely on them) from starting.

3. Network Congestion and NLB Failure: As services tried and failed to communicate, a load storm ensued. This resulted in failures in the Network Load Balancer (NLB) health checks, which further degraded network connectivity across critical services like Lambda and CloudWatch.

In summary, a seemingly isolated DNS issue for a core database service rapidly caused subsequent failures in compute provisioning and internal networking, paralyzing control plane operations across the region and beyond.

3. Troubleshooting and Resolution

The resolution involved a multi-stage process of isolation, throttling, and recovery.

1. DNS Fix: AWS engineers quickly corrected the DynamoDB DNS resolution issue.

2. Throttling: To prevent the cascading failures from worsening and to stabilize the internal network, AWS took the critical step of throttling certain operations, specifically limiting requests for new EC2 instance launches and slowing down queue processing for Lambda functions.

3. Systematic Restoration: Mitigation steps were applied to restore the Network Load Balancer health checks and recover the EC2 internal subsystems.

4. Gradual Recovery: As internal health improved, AWS gradually reduced the throttling limits. Instance launches and other services slowly returned to pre-event levels across the affected Availability Zones, followed by the backlog of queued requests being fully processed.

4. Best Practices for Customer Resilience (Vendor Users)

The outage highlighted that while Multi-AZ deployment protects against a single data center failure, a Regional-level failure requires more extensive architectural planning. To avoid significant impact from future regional outages, AWS users should adopt the following strategies:

A. Prioritize Multi-Region Architecture

Strategy	AWS Tools	Goal
Active-Passive (Pilot Light)	AWS Route 53, Cross-Region Read Replicas (RDS/Aurora), S3 CRR.	Maintain a minimal-resource standby stack in a secondary Region. On failure, promote the database and scale up compute. Lower cost, but requires minutes of recovery time (RTO).
Active-Active	AWS Global Accelerator, DynamoDB Global Tables, Route 53 with Latency/Geo Routing.	Run full production stacks in two or more Regions simultaneously. All users are served from the closest Region. Provides near-zero downtime, but is significantly more costly and requires complex data synchronization.

B. Decouple and Isolate Dependencies

1. Decouple Control Plane Operations: Recognize that core services like IAM and STS may rely on US-EAST-1. Design your application to tolerate the loss of the control plane (e.g., cannot launch new resources) while maintaining the data plane (already running resources).

2. Utilize Regional Endpoints: Explicitly configure AWS SDKs and tools to use Regional endpoints instead of global ones where available, reducing reliance on US-EAST-1 for region-specific operations.

3. Cross-AZ Deployments (Tier 1 Baseline): Always ensure that critical services (EC2 Auto Scaling Groups, RDS, Load Balancers) are distributed across a minimum of three Availability Zones within your primary Region.

C. Enhance Observability and Communication

1. External Status Page: Do not host your incident communication channels (status page, recovery documentation) within the same AWS Region, or even on AWS itself. Use a separate service or provider to guarantee communication during a full regional outage.

2. Define RTO/RPO: Clearly define your Recovery Time Objective (RTO—how long can you be down) and Recovery Point Objective (RPO—how much data loss is acceptable) to justify the cost and complexity of Multi-Region solutions.

This incident reinforces the lesson that resilience is not the prevention of failure, but the architectural ability to survive it.

The video below discusses the advanced considerations and trade-offs when designing applications to span multiple geographic AWS regions for improved resilience.

Best practices for creating multi-Region architectures on AWS is a helpful resource for understanding the different models like active-active and active-passive deployments.

A view on Lakehouse Architecture

 Deploying a SQL Data Warehouse over a Data Lake—often referred to as a "Lakehouse" architecture—combines the scalability and flexibility of a Data Lake with the structured querying power of a Data Warehouse. Here's a comprehensive deployment plan ......

🧭 Phase 1: Strategy & Architecture Design

🔹 Define Objectives

• Enable structured analytics over semi-structured/unstructured data

• Support BI tools (e.g., Power BI, Tableau) via SQL endpoints

• Ensure scalability, cost-efficiency, and governance

🔹 Choose Technology Stack

Layer	Azure Option	AWS Option
Data Lake	Azure Data Lake Storage Gen2	Amazon S3
SQL Warehouse	Azure Synapse Analytics / Fabric	Amazon Redshift Spectrum
Metadata Catalog	Azure Purview	AWS Glue Data Catalog
Orchestration	Azure Data Factory	AWS Step Functions / Glue ETL
CI/CD	Azure DevOps / GitHub Actions	AWS CodePipeline / GitHub

🏗️ Phase 2: Data Lake Foundation

🔹 Provision Storage

• Create hierarchical namespace-enabled containers

• Define folder structure: /raw/, /curated/, /sandbox/

🔹 Ingest Raw Data

• Use ADF pipelines or Glue jobs to ingest from sources (RDBMS, APIs, logs)

• Apply schema-on-read using Parquet/Delta formats

🔹 Implement Governance

• Tag datasets with business metadata

• Register assets in Purview or Glue Catalog

🧱 Phase 3: SQL Warehouse Layer

🔹 Create External Tables

• Use CREATE EXTERNAL TABLE to define schema over Data Lake files

• Partition by date or business keys for performance

🔹 Optimize Performance

• Use columnar formats (Parquet, Delta)

• Enable caching or materialized views for frequent queries

• Implement statistics and auto-refresh policies

🔹 Enable BI Connectivity

• Expose SQL endpoints

• Configure ODBC/JDBC for Power BI/Tableau

🔁 Phase 4: CI/CD & Automation

🔹 Infrastructure as Code

• Use ARM templates or Terraform for Synapse/Redshift setup

• Script Data Lake provisioning and access policies

🔹 Pipeline Automation

• Build ADF pipelines with parameterized datasets

• Use Git integration for version control

• Deploy via DevOps YAML or PowerShell scripts

🔹 Monitoring & Alerts

• Integrate with Azure Monitor or CloudWatch

• Set up alerts for pipeline failures, query latency, and storage thresholds

🔐 Phase 5: Security & Compliance

🔹 Access Control

• Use RBAC and ACLs for Data Lake

• Implement row-level and column-level security in SQL layer

🔹 Data Protection

• Encrypt data at rest and in transit

• Mask sensitive fields using dynamic data masking

🔹 Audit & Compliance

• Enable logging for query access and data modifications

• Integrate with compliance tools (e.g., Microsoft Defender, AWS Macie)

📊 Phase 6: Validation & Rollout

🔹 Test Scenarios

• Validate SQL queries across raw and curated zones

• Perform load testing and concurrency checks

🔹 Stakeholder Training

• Provide SQL access guides

• Conduct workshops for analysts and data scientists

🔹 Rollout Strategy

• Start with a pilot domain (e.g., Sales or Finance)

• Gradually onboard other domains

Here's a clean, professional deployment diagram and CI/CD template tailored for deploying a SQL Data Warehouse over a Data Lake in Azure. You can adapt this for AWS or hybrid environments as needed.

🧭 Architecture Diagram: SQL Data Warehouse over Data Lake (Azure)

Code

+----------------------------+       +----------------------------+
|   Source Systems          |       |   External Data Sources    |
| (ERP, CRM, APIs, Files)   |       | (Web, FTP, SaaS, IoT)      |
+------------+--------------+       +------------+---------------+
             |                                   |
             v                                   v
+----------------------------+       +----------------------------+
| Azure Data Factory (ADF)   |<----->|   CI/CD Pipeline (DevOps) |
| - Ingest & Transform       |       |   - YAML / ARM / PowerShell|
+------------+--------------+       +----------------------------+
             |
             v
+----------------------------+
| Azure Data Lake Storage    |
| - Raw Zone (/raw/)         |
| - Curated Zone (/curated/) |
| - Sandbox Zone (/sandbox/) |
+------------+--------------+
             |
             v
+----------------------------+
| Azure Synapse / Fabric     |
| - External Tables (SQL)    |
| - Views / Materialized     |
| - SQL Endpoints for BI     |
+------------+--------------+
             |
             v
+----------------------------+
| BI Tools / Consumers       |
| - Power BI, Tableau        |
| - Analysts, Data Scientists|
+----------------------------+

⚙️ CI/CD Template: Azure DevOps YAML (ADF + Synapse)

yaml

trigger:
  branches:
    include:
      - main

variables:
  environment: 'dev'
  resourceGroup: 'rg-data-lakehouse'
  location: 'westeurope'

stages:
- stage: DeployADF
  jobs:
  - job: DeployADF
    steps:
    - task: AzureResourceManagerTemplateDeployment@3
      inputs:
        deploymentScope: 'Resource Group'
        azureResourceManagerConnection: 'AzureServiceConnection'
        subscriptionId: '$(subscriptionId)'
        action: 'Create Or Update Resource Group'
        resourceGroupName: '$(resourceGroup)'
        location: '$(location)'
        templateLocation: 'Linked artifact'
        csmFile: 'arm/adf-template.json'
        overrideParameters: '-factoryName $(adfName)'

- stage: DeploySynapse
  jobs:
  - job: DeploySQL
    steps:
    - task: SqlAzureDacpacDeployment@1
      inputs:
        azureSubscription: 'AzureServiceConnection'
        ServerName: '$(synapseServer)'
        DatabaseName: '$(synapseDB)'
        SqlUsername: '$(sqlUser)'
        SqlPassword: '$(sqlPassword)'
        DacpacFile: 'sql/synapse.dacpac'

A version for AWS (Redshift Spectrum + S3 + Glue) or a hybrid setup is below....

🌐 Hybrid Lakehouse Architecture: Azure + AWS

🧱 Core Components

Layer	Azure Stack	AWS Stack
Data Lake	Azure Data Lake Storage Gen2	Amazon S3
SQL Warehouse	Azure Synapse / Fabric	Amazon Redshift Spectrum
Metadata Catalog	Azure Purview	AWS Glue Data Catalog
ETL/Orchestration	Azure Data Factory	AWS Glue / Step Functions / Airflow
CI/CD	Azure DevOps / GitHub Actions	AWS CodePipeline / GitHub
BI Tools	Power BI, Tableau	QuickSight, Tableau

🧭 Deployment Plan

🔹 Phase 1: Foundation Setup

• Provision S3 buckets and ADLS Gen2 containers with matching folder structures (/raw/, /curated/, /sandbox/)

• Set up cross-cloud identity federation (e.g., Azure AD ↔ IAM roles)

🔹 Phase 2: Data Ingestion

• Use ADF and Glue to ingest data from sources into respective lakes

• Apply schema-on-read using Parquet or Delta formats

🔹 Phase 3: SQL Layer Integration

• Create external tables in Synapse and Redshift Spectrum pointing to lake zones

• Use shared metadata via Purview ↔ Glue integration (manual or via APIs)

🔹 Phase 4: CI/CD Automation

• Use Terraform or Pulumi for cross-cloud provisioning

• Automate pipeline deployment via Azure DevOps and AWS CodePipeline

• Store SQL scripts and ETL logic in GitHub with environment branching

🔹 Phase 5: BI & Consumption

• Expose SQL endpoints from both Synapse and Redshift

• Use semantic layers (e.g., AtScale) for unified business logic

• Connect Power BI, Tableau, or QuickSight to both endpoints

🔹 Phase 6: Governance & Security

• Apply RBAC and IAM policies across clouds

• Encrypt data at rest and in transit

• Enable audit logging and data classification

🗺️ Architecture Diagram (Hybrid)

Code

+----------------------------+       +----------------------------+
|   Source Systems           |       |   External Data Sources    |
| (ERP, CRM, APIs, Files)    |       | (Web, SaaS, IoT, FTP)      |
+------------+--------------+       +------------+---------------+
             |                                   |
             v                                   v
+----------------------------+       +----------------------------+
| Azure Data Factory (ADF)   |       | AWS Glue / Airflow         |
| - Ingest & Transform       |       | - ETL & Cataloging         |
+------------+--------------+       +------------+---------------+
             |                                   |
             v                                   v
+----------------------------+       +----------------------------+
| Azure Data Lake Gen2       |       | Amazon S3                  |
| - Raw / Curated / Sandbox  |       | - Raw / Curated / Sandbox  |
+------------+--------------+       +------------+---------------+
             |                                   |
             v                                   v
+----------------------------+       +----------------------------+
| Azure Synapse / Fabric     |       | Amazon Redshift Spectrum   |
| - External Tables (SQL)    |       | - External Tables (SQL)    |
| - Views / Materialized     |       | - Views / Materialized     |
+------------+--------------+       +------------+---------------+
             |                                   |
             v                                   v
+----------------------------+       +----------------------------+
| BI Tools / Semantic Layer  |<----->| BI Tools / Semantic Layer  |
| - Power BI, Tableau        |       | - QuickSight, Tableau      |
+----------------------------+       +----------------------------+

📚 References & Guides