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Reliability

Reliability is the ability of a system to perform its required functions under stated conditions for a specified period of time.

Key Concepts​

Fault Tolerance​

  • System's ability to continue operating properly in the event of failure
  • Redundancy: Having backup components
  • Failover: Automatic switching to backup systems

High Availability​

  • System's ability to remain operational for a long period of time
  • Measured as a percentage of uptime
  • Common targets: 99.9% (Three nines) to 99.999% (Five nines)

Disaster Recovery​

  • Process of restoring systems after a catastrophic failure
  • Recovery Time Objective (RTO)
  • Recovery Point Objective (RPO)

Reliability Patterns​

Redundancy​

  • Active-Active: All systems are running simultaneously
  • Active-Passive: Backup systems are on standby
  • Geographic Redundancy: Systems in different locations

Health Checks​

  • Regular monitoring of system components
  • Automated recovery procedures
  • Alerting systems for failures

Data Backup​

  • Regular backups
  • Multiple backup locations
  • Backup verification

Best Practices​

  1. Design for Failure

    • Assume everything will fail
    • Implement graceful degradation
    • Use circuit breakers

  2. Monitoring and Alerting

    • Real-time monitoring
    • Automated alerts
    • Incident response procedures

  3. Testing

    • Chaos testing
    • Failure injection
    • Recovery testing

Common Challenges​

  • Cost of redundancy
  • Complexity in distributed systems
  • Balancing reliability with performance
  • Managing technical debt

Further Reading​