# Disaster Recovery

## Overview

Disaster Recovery (DR) ensures business continuity when disasters occur. This guide covers backup strategies, recovery objectives, DR plans, and implementation patterns.

## Key Metrics

### RTO (Recovery Time Objective)

**Maximum Acceptable Downtime:**
- Time to restore service
- Business impact tolerance
- Drives backup frequency

### RPO (Recovery Point Objective)

**Maximum Data Loss:**
- Acceptable data loss window
- Frequency of backups
- Drives replication strategy

## Backup Strategies

### Full Backups

**Complete System Backup:**
- Everything included
- Longer backup time
- More storage required
- Full restoration

### Incremental Backups

**Changes Since Last Backup:**
- Faster backups
- Less storage
- Requires full + incrementals for restore

### Differential Backups

**Changes Since Full Backup:**
- Moderate backup time
- Moderate storage
- Full + latest differential for restore

### Continuous Backup

**Real-time Replication:**
- Minimal data loss
- Higher cost
- Complex implementation

## DR Strategies

### Backup and Restore

**Simple Approach:**
- Regular backups
- Restore from backup
- Lower cost
- Higher RTO/RPO

### Pilot Light

**Minimal Infrastructure:**
- Core services running
- Scale up on disaster
- Moderate cost
- Moderate RTO

### Warm Standby

**Active Standby:**
- Replicated environment
- Smaller instance sizes
- Scale up on disaster
- Lower RTO

### Multi-Site Active-Active

**Both Sites Active:**
- Full replication
- Load balanced
- Lowest RTO/RPO
- Highest cost

## Implementation

### Backup Automation

**Automated Backups:**
```yaml
# Scheduled backups
schedule: "0 2 * * *"  # Daily at 2 AM
retention: 30 days
backup_type: incremental
```

### Cross-Region Replication

**Geographic Redundancy:**
- Replicate to multiple regions
- Reduce regional failure risk
- Meet compliance requirements

### Testing

**Regular DR Drills:**
- Test backup restoration
- Verify recovery procedures
- Train team
- Update documentation

## Cloud-Specific Patterns

### AWS

**Services:**
- AWS Backup
- Cross-region replication
- Multi-AZ deployments
- Route 53 failover

### GCP

**Services:**
- Cloud Storage backups
- Cross-region replication
- Cloud SQL backups
- Cloud Load Balancing

### Azure

**Services:**
- Azure Backup
- Azure Site Recovery
- Geo-redundant storage
- Traffic Manager

## Best Practices

1. **Define RTO/RPO:** Based on business requirements
2. **Automate Backups:** Regular, automated backups
3. **Test Regularly:** DR drills and exercises
4. **Document Procedures:** Step-by-step recovery
5. **Multi-Region:** Geographic redundancy
6. **Monitor Backups:** Verify success
7. **Version Control:** DR plans in version control
8. **Train Team:** Regular training
9. **Update Plans:** Keep current with infrastructure
10. **Regular Reviews:** Quarterly DR reviews

