5 · Database Resilience — Revise
Resilient · 26% · Compressed recall. Read the
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Multi-AZ vs Read Replica
|
Multi-AZ |
Read Replica |
| Purpose |
HA / failover |
Read scaling |
| Replication |
Synchronous |
Asynchronous (can lag) |
| Standby readable? |
No |
Yes |
| Failover |
Automatic, same endpoint |
Manual promote |
| Scope |
Another AZ, same Region |
Same/cross-AZ or cross-Region |
| Count |
1 standby |
up to 15 (MySQL/MariaDB/PostgreSQL) |
Goal → feature
| Goal |
Feature |
| Auto failover, no data loss |
RDS Multi-AZ |
| Offload reads |
RDS Read replicas |
| Cross-Region relational DR (fast) |
Aurora Global Database (RPO ~1s, RTO ~1min) |
| Global active-active NoSQL |
DynamoDB Global Tables |
| Cheap RDS DR |
Cross-Region read replica / copied snapshots |
Aurora / DynamoDB facts
| Fact |
Value |
| Aurora data copies |
6 across 3 AZs (self-healing) |
| Aurora replicas |
up to 15, any = failover target |
| Aurora endpoints |
writer (cluster), reader (load-balanced), custom |
| Aurora Global DB |
1 primary + up to 5 secondary Regions, <1s replication |
| DynamoDB default |
Multi-AZ (3 copies), automatic |
| DynamoDB Global Tables |
Multi-Region active-active (multi-master) |
| DynamoDB PITR |
Restore to any second in last 35 days |
| RDS automated backup retention |
0–35 days (0 = off) |
| Manual snapshots |
Persist until deleted; copy cross-Region / share |
Flashcards
"Offload read/reporting queries" — which RDS feature?
Read replicas (async, read-only). NOT Multi-AZ — its standby can't serve reads.
"Automatic failover with no data loss" — which RDS feature?
Multi-AZ (synchronous standby, automatic failover on the same endpoint).
Is a read replica automatic HA?
No — asynchronous (may lag) and failover is a manual promotion.
How many copies of Aurora data, and where?
6 copies across 3 Availability Zones, continuously self-healing.
Fast cross-Region DR for a relational DB?
Aurora Global Database — sub-second replication, RPO ~1s, RTO ~1min.
Global active-active NoSQL with local low-latency writes?
DynamoDB Global Tables (multi-Region, multi-master).
Max RDS automated backup retention?
35 days (0 disables). Manual snapshots persist until you delete them.
Aurora reader endpoint does what?
Load-balances read connections across the Aurora Replicas.
Common traps
- Multi-AZ = availability; Read Replica = read scaling. Don't swap.
- Standby isn't readable; read replica isn't auto-failover.
- Aurora: 6 copies / 3 AZs, 15 replicas.
- Aurora Global DB for fast cross-Region relational DR; DynamoDB Global Tables for
active-active NoSQL.
- DynamoDB is multi-AZ by default (no config).
- Automated backups max 35 days; snapshots copyable cross-Region for DR.