AWS High Availability and Disaster Recovery

Core Concepts and Definitions

Business Continuity vs. Disaster Recovery

• Business Continuity (BC)

  • Focus on minimizing business disruption

  • Preventive and planning measures

  • Defines acceptable service levels

• Disaster Recovery (DR)

  • Response to events threatening continuity

  • Reactive measures and procedures

  • Implementation of recovery plans

Fault Tolerance vs. High Availability

• Fault Tolerance

  • Complete ability to tolerate faults

  • No user-visible disruption

  • Often more expensive to implement

  • Zero downtime objective

• High Availability

  • Allows for minimal unplanned downtime

  • More cost-effective approach

  • Balance between reliability and cost

  • Accepts some potential disruption

Service Level Concepts

Service Level Agreements (SLA)

• Commitments for quality/availability

• Not absolute guarantees

• May include compensation provisions

• Requires customer documentation for claims

Recovery Objectives

1. Recovery Time Objective (RTO)

   • Time to restore business processes

   • Measured from disruption to recovery

   • Defines acceptable downtime

   • Key factor in BC planning

2. Recovery Point Objective (RPO)

   • Acceptable data loss measured in time

   • Gap between last backup and incident

   • Influences backup strategy

   • Drives data protection requirements

Real-World Example: The S3 Outage of 2017

Incident Overview

• Date: February 28, 2017

• Location: AWS Northern Virginia (us-east-1)

• Duration: 252 minutes

• Cause: Human error during system maintenance

Impact Analysis

• Exceeded 99.99% availability goal

• Affected multiple dependent services

• Disrupted AWS's own health dashboard

• Demonstrated cascading failure risks

Lessons Learned

• Human error can bypass safeguards

• Dependencies create vulnerability chains

• Need for cross-region resilience

• Importance of proper change management

Types of Disasters

Infrastructure Failures

1. Hardware Failures

   • Network equipment malfunctions

   • Storage system crashes

   • Physical infrastructure issues

2. Software Failures

   • Deployment errors

   • Configuration mistakes

   • Application crashes

External Threats

1. Load-Related

   • DDoS attacks

   • Traffic spikes

   • Resource exhaustion

2. Infrastructure

   • Fiber cuts

   • Power outages

   • Facility issues

Data and System Issues

1. Data-Induced

   • Corruption

   • Type conversion errors

   • Invalid data processing

2. Credential Issues

   • Certificate expirations

   • Key rotations

   • Authentication failures

Resource Limitations

1. Capacity Issues

   • Instance type unavailability

   • Storage limitations

   • Network bandwidth constraints

2. Identifier Exhaustion

   • IP address depletion

   • Resource ID limitations

   • Namespace conflicts

Best Practices

Planning and Prevention

• Regular backup testing

• Documentation maintenance

• Staff training

• Change management procedures

Implementation Strategies

1. Multi-AZ Deployment

   • Cross-zone redundancy

   • Load balancing

   • Automatic failover

2. Cross-Region Solutions

   • Geographic distribution

   • Data replication

   • Traffic routing

3. Dependency Management

   • Service decoupling

   • Circuit breakers

   • Fallback mechanisms

Monitoring and Response

• Real-time monitoring

• Automated alerts

• Incident response procedures

• Regular testing and drills

Werner Vogels' Principle

"Everything fails all the time" - Werner Vogels, Amazon CTO

This principle emphasizes:

• Assume failure will occur

• Design for resilience

• Plan for recovery

• Test failure scenarios

Implementation Considerations

Cost vs. Reliability

• Balance between protection and expense

• Tiered recovery solutions

• Risk-based investments

• Cost-benefit analysis

Testing Requirements

• Regular DR drills

• Failure simulation

• Recovery validation

• Documentation updates

Compliance and Reporting

• SLA monitoring

• Incident documentation

• Recovery metrics

• Compliance validation