- Availability is
- period of time when a service is available
- time required by a system to respond to a request made by a user.
- expressed as % of how much uptime is expected
- Example, 99% of availability for one year can have up to 3.65 days of downtime (1%).
- High Availability is systems with
- minimum downtime
- minimum service interruption
- Implement HA by
- eliminate single points of failure in your infrastructure
- putting redundant components for same task
- adding the load balancer above it, to detect failures and adapt for timely recovery
| Failure Points | AWS Services/Solution |
| DNS/Domain Services | Route53 |
| Load Balance | Elastic Load Balancing |
| Web/Application Server | Auto-Scaling |
| Database Servers | Redundant nodes or clustering |
| Authentication | Redundant nodes |
| Data Center Failures | Use Multiple Availability Zone |
| Disaster | Use Multiple Regions |
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