RPO is tolerated data loss measured in time. RTO is tolerated recovery time. They are business requirements, not service features.
| Strategy | Running footprint | Relative RTO/RPO | Cost |
|---|---|---|---|
| Backup and restore | Backups only | Highest | Lowest |
| Pilot light | Critical core running | Lower | Low-medium |
| Warm standby | Scaled-down full stack | Lower still | Medium-high |
| Multi-site active/active | Full production in multiple sites | Lowest | Highest |
High availability typically survives component or AZ failure inside a Region. Disaster recovery addresses larger failures and operational recovery. A Multi-AZ database is not automatically a cross-Region DR plan.
Match migration tool to what moves
- DMS migrates databases and can keep replicating changes; SCT converts heterogeneous schemas.
- Application Migration Service moves servers into AWS.
- Elastic Disaster Recovery maintains recovery capability for servers.
- DataSync transfers online files/object data.
- Snow Family handles large offline transfer or constrained networks.
- Application Discovery Service inventories dependencies; Migration Hub tracks migration progress.
Backups need tested restores, retention, encryption, and isolation. AWS Backup centralizes policy; Vault Lock helps enforce retention. Replication can also replicate corruption, so immutable recovery points still matter.
Exam lens: if two options meet RTO/RPO, choose the less expensive and operationally simpler one. Do not buy active/active when warm standby satisfies the business target.
Review card
- RPO is data loss; RTO is downtime.
- Multi-AZ HA and Multi-Region DR are different scopes.
- Replication is not a substitute for immutable backup.
- DMS moves databases; MGN moves servers; DRS prepares server recovery.
- A DR design is incomplete until failover and restore are tested.
RPO 是可接受的資料遺失時間；RTO 是可接受的復原時間。它們是 business requirements，不是 service feature。
| Strategy | Running footprint | 相對 RTO/RPO | 成本 |
|---|---|---|---|
| Backup and restore | 只有 backup | 最高 | 最低 |
| Pilot light | Critical core 持續運作 | 較低 | 低到中 |
| Warm standby | 縮小的完整 stack | 更低 | 中到高 |
| Multi-site active/active | 多站點 full production | 最低 | 最高 |
High availability 通常應對 Region 內 component/AZ failure；DR 應對更大範圍故障與營運復原。Multi-AZ database 不會自動變成 cross-Region DR。
依搬移對象選工具
- DMS 搬 database 並可持續 replicate change；SCT 轉 heterogeneous schema。
- Application Migration Service 搬 server 進 AWS。
- Elastic Disaster Recovery 維持 server recovery capability。
- DataSync 搬 online file/object data。
- Snow Family 處理大量 offline transfer 或 network 受限。
- Application Discovery Service 盤點 dependency；Migration Hub 追蹤進度。
Backup 要有 tested restore、retention、encryption 與 isolation。AWS Backup 中央管 policy；Vault Lock 幫助強制 retention。Replication 也可能複製 corruption，所以 immutable recovery point 仍然重要。
考試視角： 兩個選項都滿足 RTO/RPO 時，選成本更低、維運更簡單的。Warm standby 已滿足就不要買 active/active。
複習卡
- RPO 看 data loss；RTO 看 downtime。
- Multi-AZ HA 與 Multi-Region DR 是不同 scope。
- Replication 不能代替 immutable backup。
- DMS 搬 database；MGN 搬 server；DRS 準備 server recovery。
- 沒有 failover/restore test 就不算完整 DR。