RDS

Relational Database Service
Database service for database engines that use SQL as a query language
Engines:
- Postgresql
- Mysql / Mariadb
- Oracle
- MSSQL
- IBM DB2
- Aurora (Proprietary AWS Relational Database)
You cannot access the underlying compute instances for RDS unless you are using RDS Custom
- RDS Custom supports Oracle and Microsoft SQL Server
RDS scales storage automatically
- You have to set the Maximum Storage Threshold (max amount of storage to use)
- Supports all RDS engines

Scale out read operations
Create up to 15 read replicas within the same AZ or across AZ’s or across regions
Replication is asynchronous
You can promote a read-replica to it’s own database capable of full writes
Network Costs
- If the read replicas is in the same region, there is no cost for replication traffic
- For cross-region replication traffic, there is a cost
You can setup read-replicas as Multi-AZ for fault tolerance

Mainly used for disaster recovery
synchronous replication to a standby database
One DNS name for both databases with automatic failover
Multi-AZ replicas cannot be read or written to until they are promoted to the primary instance
Converting from single-AZ to multi-AZ requires no downtime. This can be done in the “modify” section of the RDS database
- A snapshot is taken and restored into a new standby database. Then a full sync of the database is initiated.

Fully managed database proxy for RDS
Allows apps to pool and share DB connections established with the database
Improving database efficiency by reducing the stress on database resources (e.g CPU, RAM)and minimize open connections (and timeouts)
Serverless, autoscaling, highly available (multi-AZ)
Reduced RDS and Aurora failover time by up 66%
Supports RDS (MySQL,PostgreSQL, MariaDB, MS SQL Server) and Aurora (MySQL, PostgreSQL)
No code changes required for most apps
Enforce IAM authentication for DB, and securely store credentials in AWS Secrets Manager
RDS proxy is never publicly accessible
RDS Proxy is useful for highly scaling lambda functions that open database connections

Aurora

Fully managed Postgres or MySQL compatible database designed by default to scale and fine-tuned to be really fast
Aurora automatically grows in increments of 10GB, up to 128 TB
5x performance over MySQL, 3x performance over Postgres

Combines the speed and availability of high-end databases with the simplicity and cost-effectiveness of open source databases
Aurora can run either MySQL or Postgres compatible engines
Aurora MYSQL is 5x better performance than traditional MySQL
Aurora Postgres is 3x better performance than traditional Postgres
Aurora Costs more than RDS (20% more) but is more efficient

6 copies of your data in 3 AZ:
- Needs only 4 out of 6 copies for writes (so if one AZ is down then it is fine)
- Need only 3 out of 6 for reads
- self healing with peer-to-peer replication
- Storage is striped across 100s of volumes
Automated failover for master happens in less than 30 seconds
Master + up to 15 Aurora Read Replicas serve reads. You can autoscale the read replicas. Clients connect to the “Reader Endpoint”, which will point to any of the read instances

Aurora Backup and Failover is handled automatically
Aurora has a feature called Backtrack that allows you to restore to any point in time without restoring from backups
Snapshots of data can be shared with other AWS accounts
Storage is self-healing , in that data blocks and disks are continuously scanned for errors and repaired automatically

	Amazon Aurora Replicas	Mysql Read Replicas
Number of Replicas	Up to 15	Up to 5
Replication Type	Asynchronous(ms)	Asynchronous (s)
Performance impact on primary	Low	High
Act as failover target	Yes (no data loss)	Yes (potentially minutes of data loss)
Automated failover	Yes	No
Support for user-defined replication delay	No	Yes
Support for different data or schema vs primary	No	Yes

Aurora except the database will automatically start up, shut down, and scale capacity up or down based on your application’s needs
Apps used a few minutes several times per day or week, eg. low-volume blog site
pay for database storage and the database capacity and I/O your database consumes while it is active