RDS Essentials:

• RDS is a fully managed Relational Database Service:
  • Does not allow access to the underlying operating system (fully-managed).
  • You connect to the RDS database server in the same way you would connect to a traditional on-premise database instance (i.e. MySQL command line).
  • RDS has the ability to provision/resize hardware on demand for scaling.
  • You can enable Multi-AZ deployments for backup and high available solutions.
  • Utilize Read Replicas (MySQL/PostgreSQL/Aurora) - to help offload hits on your primary database.
  • Relational databases are databases that organize stored data into tables.
  • The associated tables have defined relationships between them.
• Database supported by RDS:
  • MySQL
  • MariaDB
  • PostgreSQL
  • Oracle
  • MS SQL Server
  • Aurora:
    • Is a home grown Relational Database that has been forked from, and fully compatible with MySQL.
    • It has five times better performance than MySQL and a lower price point than commercial database.
• Benefits of running RDS instead of database on your own instance:
  • Automatic minor updates.
  • Automatic backups (point-in-time snapshots).
  • Not required to managed operating system.
  • Multi-AZ with a single click.
  • Automatic recovery in event of a failover.

RDS Multi-AZ Failover:

• Multi-AZ failover (Automatic AZ-Failover) synchronously replicated data to backup (stand-by) database instance located in another availability zone (but in the same region).
• In the event of:
  • Service outage in an AZ.
  • Primary DB instance failure.
  • Instance server type is changed.
  • Manual failover initiated.
  • Updating software version.
  • AWS will automatically switch the CNAME DNS record from the primary instance to the stand-by instance.

• RDS backups are taken against the stand-by instance to reduce I/O freezes and slow down if Multi-AZ is enabled.

• In order for Multi-AZ to work, your primary database instance must be launched into a "subnet group".

  • NOTE: An RDS instance must be launched into a subnet (inside a VPC), just like an EC2 instance. So the same security/connectivity rules, and highly available/fault tolerant concepts apply.

RDS Backups:

• AWS provides automated point-in-time backups against the RDS database instance.
• Automated backups are deleted once the database instance is deleted and cannot be recovered (but you can take your own snapshots of backups before deleting).
• Backups on database engines only work correctly when the database engine is "transactional", but do currently work for all supported database types.
• MySQL requires InnoDB for reliable backups.

RDS Read Replicas:

• Read replicas are asynchronous copies of the primary database that are used for read only purpose (only allow "read connections").
• When you write new data to the primary database, AWS copies it for you to the read replica.
• You can create and have multiple read replicas for a primary database.
• Read replicas can be created from other read replicas (so no performance hit on the primary database).
• MySQL, MariaDB, PostgreSQL and Aurora currently support read replicas.
• You can monitor replication lag using CloudWatch.

Benefits of using Read Replicas

• Read replicas allow for all read traffic to be redirected from the primary database to the read replica. This will greatly improve performance on the primary database.
• Read replicas allow for elasticity in RDS - you can add more read replicas as demand increases.
• You can promote a read replica to a primary instance.
• MySQL:
  • Replicate for importing/exporting data to RDS.
  • Can replicate across regions.

When should you use Read Replicas

• High volume, non-cached database read traffic (elasticity).
• Running business function such as data warehousing.
• Importing/Exporting data into RDS.
• Rebuilding indexes:
  • Ability to promote a read replica to a primary instance.