High Availability - Disaster Recovery

  • Disaster Recovery (DR) is about preparing for and recovering from a disaster
    • Disaster: events that have negative impact on business continuity or finances
  • Recovery types to cloud:
    1. On-premise => On-premise: Traditional DR, very expensive
    2. On-premise => Cloud: Hybrid recovery
    3. Cloud => Cloud: e.g. AWS Cloud Region A => AWS Cloud Region B
  • 📝Terminology
    • RPO: Recovery Point Objective
      • The amount of data loss you’re willing to accept
      • Based on:
        • How back in time you can recover
        • How often you take back-up
    • RTO: Recovery Time Objective
      • Amount of downtime you’re willing to accept
  • Disaster Recovery Strategies
    • From business continuity to uninterrupted business:
      • Backup and Restore -> Pilot Light -> Warm / Hot Standby -> Hot Site / Multi Site
    • Backup and Restore
      • Cheapest option, slowest RTO.
      • Take frequent snapshots of your data:
        • from e.g. EBS Volumes, RDS databases, EC2 AMI’s
        • to e.g. S3
      • AWS Storage Gateway enables from on-premises to cloud back-up seamlessly
      • Disaster Recovery - Backup and Restore
    • Pilot Light
      • Critical core element(s) of the app is always running in the cloud
        • Faster than Backup and Restore as critical systems are already up.
      • Example of active/passive failover configuration.
      • From networking, you have two options: Elastic IP addresses or Elastic Load Balancing (ELB)
        • DNS records to point to EC2 or point to LB using CNAME.
      • Changed data in DR site after failover must be reversed back to primary site after failback.
      • Disaster Recovery - Pilot Light
    • Warm / Hot Standby
      • Scaled-down full production environment always running in the cloud.
        • Upon disaster, we can scale to production load
      • Example of active/passive failover configuration.
      • Changed data in DR site after failover must be reversed back to primary site after failback.
      • Disaster Recovery - Warm / Hot Standby
    • Hot Site / Multi Site
      • Full Production Scale is running AWS and on-premise
      • Example of active-active failover configuration.
      • Changed data in DR site after failover must be reversed back to primary site after failback.
      • 💡 In Route 53: You configure active-active failover using any routing policy (or combination of routing policies) other than failover.
      • Disaster Recovery - Multi site / Hot Site / Active - Active
  • 💡 Disaster Recovery Tips
    • Backup
      • EBS Snapshots, RDS automated backups / Snapshots, etc…
      • Regular pushes to S3 / S3 IA / Glacier, Lifecycle Policy, Cross Region Replication
      • From On-premise: Snowball or Storage Gateway
    • High Availability
      • Use Route 53 to migrate DNS over from Region to Region
      • RDS Multi-AZ, ElastiCache Multi-AZ, EFS, S3
      • Site to Site VPN As a recovery from Direct Connect
    • Replication
      • RDS Replication (Cross Region), AWS Aurora + Global Databases
      • Database replication from on-premise to RDS
      • Storage Gateway
    • Automation
      • CloudFormation / Elastic Beanstalk to re-create a whole new environment
      • Recover / Reboot EC2 instances with CloudWatch if alarms fail
      • AWS Lambda functions for customized automations
    • 🤗 Chaos
      • Netflix has a “simian-army” randomly terminating EC2.
        • Chaos monkeys terminates instances in production.

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