The difference between High Availability (HA) and Disaster Recovery (DR) is that HA is concerned with the technical goal of achieving a particular availability metric (e.g. number of nines) and DR concerns planning for what actions to take before, during, and after a disaster occurs. With respect to AWS, Availability Zones (AZ) address HA while Regions address DR.
Note Amazon S3 is eleven 9s of durability and four nines of availability. Which means the probability of losing data is much lower than the actual availability (i.e. your data might not be available, but it probably is not lost).
Tools to achieve HA:
| Availability % | Downtime per Year | Downtime per Month |
| 99.999 | 5.26 minutes | 26.30 seconds |
| 99.99 | 52.60 minutes | 4.38 minutes |
| 99.9 | 8.77 hours | 43.83 minutes |
| 99 | 3.65 days | 7.31 hours |
| 90 | 36.53 days | 73.05 hours |
Note Amazon S3 is eleven 9s of durability and four nines of availability. Which means the probability of losing data is much lower than the actual availability (i.e. your data might not be available, but it probably is not lost).
Tools to achieve HA:
- Auto Scaling Groups. Horizontal scaling as a workload increases
- EC2 instance model upgrade (vertical scaling)
- Elastic Load Balancers
- Route 53 (DNS)
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