Ref: https://learn.cantrill.io/courses/1820301/lectures/41301419

• Summary:
• Contents:

Amazon Relational Database Service (RDS) - Key Concepts

• 🔧 Provides AWS-managed DB servers (called RDS instances)
  • Similar to on-premises DB servers, but with important benefits:
    • 👍 No need to manage HW, OS nor installation
    • 👍 Maintenance of the DB engine mostly managed by AWS
    • 👍 Integration with other AWS products
  • 👎 No OS-level access nor access via SSH (because it's an AWS-managed service)
    • 💡 RDS Custom: a variant of RDS where you DO have some more low-level access
      • In general, though, assume RDS does not provide this low-level access
• ‼️ NOT a DBaaS (DB-as-a-Service)!! It is a DBSERVERaaS (DBServer-as-a-Service)!
  • DBaaS = You pay for a DB
  • With RDS you pay for a DB server/instance (where you can host multiple DBs)
  • 💡 RDS is loosely based on EC2, RDS and EC2 instances share a lot of characteristics
• Supported DB Engines:
  • FOSS (free & open source SW): MySQL, MariaDB, PostgreSQL
  • Commercial DBs: Oracle, MS SQL Server → licensing implications
• ‼️ Amazon Aurora is a different product!
  • Aurora is a custom DB engine & product created and designed entirely by AWS, with compatibility with some of the above engines
  • Aurora has differences/improvements in many RDS features → Keep them separated

RDS - Architecture

Diagram: https://github.com/acantril/aws-sa-associate-saac03/blob/main/1300-RELATIONAL_DATABASE_SERVICE(RDS)/00_LEARNINGAIDS/RDSArch-1.png

• RDS runs within a VPC in a specific region
  • An RDS instance operates in a subnet of the VPC
  • Normal VPC access conditions apply
    • Access to RDS instances in private VPCs: VPN, Direct Connect (DX), VPC peering…
    • RDS instances in public VPCs can potentially be given public IP addresses to be accessed from public internet… but really frowned upon from a security perspective!
  • RDS instances can be accessed with DNS CNAMEs
• An RDS instance can host multiple DBs
• DB subnet group = (conceptually) list of VPC subnets where RDS can deploy 1+ instances
  • Can contain subnets from different AZs where the VPC is deployed
  • A DB subnet group must always be chosen when launching an RDS instance
    • ❗Doesn't matter if RDS instance is HA or not!
  • Can be used by many RDS instances
    • All instances with the same DB subnet group will use the same defined subnets
    • Splitting DBs into many different subnets requires multiple DB subnet groups
  • Best practice: one DB subnet group per single RDS deployment
    • 💡 Adrian's preference → gives best overall flexibility
  • Deployment
    • RDS picks subnet(s) at random unless you indicate a specific preference
    • If Multi-AZ mode is enabled, one subnet for a primary instance and another for a standby, both in different AZs
• Multi-AZ mode: if enabled, RDS instances are in different AZs
  • Primary and standby each deployed to different AZs
  • Primary and standby each have their own dedicated EBS storage
    • ❗ Different to how Aurora handles storage!
  • Synchronous replication from primary to standby (Data replicated as soon as received)
  • Backups happen from the standby instance → no negative performance impact
• Backups (EBS Snapshots) to AWS-managed S3 bucket (not visible in console)
  • S3 data replicated across multiple AZs in the region (data safe from AZ failures)
• 0+ Read Replicas
  • Asynchronous replication
  • Same or cross region
  • Use cases:
    • scaling read load
    • adding layers of resilience (allows recovering in a different region)

RDS - Billing