AWS Disaster Recovery

Concepts

RPO - recovery point objective (how much data loss is acceptable, e.g. updates from last 5 minutes can be lost)

RTO - recovery time objective (how long should it maximally take to restore the data from backup, e.g. 5 hours)

Scenarios

• Backup&Restore ($)
• • Glacier
  • S3
  • Storage Gateway
  • • Cached volumes (S3 is authority)
    • VTL - backup target for tapes
  • Transfer
  • • DX
    • Import/Export
    • Internet
  • Long RTO, High RPO
• Pilot Light ($$)
• • Minimal version of critical core components always running
  • • Database server (e.g. asynchronous replication)
  • Preconfigured server AMIs - can be started quickly
• Warm standby ($$$)
• • Scaled down version of environment running all the time
  • Can be used for non-production work
  • • Test, QA, internal use
  • Patch on same schedule as primary
  • App tier & standby-by site write to both primary and stand-by
  • Upon recovery
  • • add more servers
    • resize instances 
    • Switch DNS to warm standby
• Multi-Site ($$$$)
• • active-active
  • Two regions at the same time
  • Route53 for weighted routing
  • Complext state management (database reconciliation)

RDS

• Multi A-Z synchronously replicates data between AZ
• • Eliminates I/O freezes during backup
  • Eliminates outage during maintenance windows
• Automatic failover
• • AZ outage
  • Primary DB fails
  • DB instance type is changed
  • OS of DB is undergoing patching
  • Manual failover initiated (reboot with failover)
  • Failover ~60s
• Daily backup (within 30 minutes "backup window")
• • Retention period configurable - number of days
  • When deleting instance all automatic backups are deleted (only manual snapshots remain)
  • Automated DB snapshot can be copied (retain indefinitely)
• RDS archives logs (point in time recovery)
• • Ability to recover to arbitrary point in time in the retention period (RPO 5 minutes)
• Use InnoDB (MyISAM will not work)
• On restore possible to change many options
• • engine (SQL Server Standard -> SQL Server Enterprise)
• Snapshots can be copied cross-region

S3

• Very high durability (11 9's)
• • Reducecd Storage cheaper but lower durability
• Replicated within region
• Possible to replicate cross-region
• • Asynchronous
• Access time: instant

Glacier

• Very high durability (like S3)
• Access time: a few hours

DynamoDB

• Backed by SSD
• Replicated in 3 AZs in a region
• DataPipeline supports
• • cross region DynamoDb copy (with filtering)
  • copy to S3

AMI

• Can be copied cross-region

EBS

• AFR - 0.5-1.0% (if < 20GB modified since last snapshot)
• Snapshots reduce AFR
• RAID does not offer that much help as all disks in array are likely to fail together
• Replicated within AZ (mirrored using proprietry technology)
• Snapshots can be copied cross-region

Business Continuity

• How business continous to operate in the event of disaster
• Fire, theft, flood