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AWS RDS

RDS​

  • Relational Database Service, a managed service
  • automated provisioning, OS patching
  • continuous backups and restore to specific timestamp (Point In Time Restore)
  • monitoring dashboards
  • read replicas for improved read performance
  • Multi AZ setup for DR (Disaster Recovery)
  • maintenance windows for upgrades
  • scaling capability (vertical and horizontal)
  • storage backed by EBS (gp2 or io1)

Storage Auto Scaling​

  • when RDS detects you are running out of free database storage, it scales automatically
  • you have to set Maximum Storage Threshold

Deployment Options​

  • Multi AZ DB instance
    • creates a primary DB instance with one standby DB instance in a different AZ
    • provides high availability and data redundancy, but the standby replica cannot serve read traffic
    • increased write and commit latency (recommend to use Provisioned IOPS for better performance)
    • auto-failover to the standby replica
  • Multi AZ DB cluster
    • creates a DB cluster with a primary DB instance and two readable standby DB instances, with each DB instance in a different AZ
    • provides high availability, data redundancy and increases capacity to serve read workloads
    • semi-synchronous replication, which requires acknowledgment from at least one reader DB instance
    • auto-failover to one of the reader DB instances
  • Single DB instance
    • creates a single DB instance with no standby DB instances
  • Read replicas
    • main purpose is scalability
    • asynchronous replication, all read replicas are accessible and can be used for read scaling
  • Multi-Region
    • main purpose is disaster recovery and local performance
    • asynchronous replication and all regions are accessible and can be used for reads
  • Multi-AZ:
    • Convert RDS instance from Single-AZ to Multi-AZ, the following happens:
      • a snapshot of your primary instance is taken
      • a new standby instance is created in a different AZ from the snapshot
      • synchronous replication is configured between primary and standby instances
      • no downtime incurred, but the latency might increase due to the synchronous replication
    • During Multi-AZ failover, the following happens:
      • failover is automatically handled by RDS without administrative intervention
      • RDS simply flips the canonical name record (CNAME) for your DB instance to point at the standby, which is in turn promoted to become the new primary
      • the failover typically completes within one or two minutes
    • The following events would case RDS to initiate a failover to the standby replica:
      • loss of availability in primary AZ
      • loss of network connectivity to primary
      • compute unit failure on primary
      • storage failure on primary

When creating a new RDS database, you can choose the Deployment options from Multi-AZ DB cluster, Multi-AZ DB instance and Multi-AZ DB instance. For existing RDS databases, you can Create new replica and the new replica can be in different regions.

RDS vs RDS Custom​

  • RDS: entire database and the OS to be managed by AWS
  • RDS Custom:
    • managed Oracle and Microsoft SQL Server database with OS and database customisation
    • full admin access to the underlying OS and the database

Security​

  • data at-rest encryption
    • master and replicas, KMS, enabled at launch time
    • un-encrypted database => DB snapshot => restore as encrypted
    • master is un-encrypted, then replicas cannot be encrypted
  • in-flight encryption: TLS-ready by default
  • IAM database authentication
  • Audit logs
  • no SSH except for RDS custom

RDS Proxy​

  • allows apps to pool and share DB connections established with the database
  • improves database efficiency by reducing stress on database resources (CPU & RAM) and minimise open connections (timeout)
  • serverless, auto-scaling, highly available (multi AZ)
  • never publicly accessible (must be accessed from VPC)
  • use case: lambda function (auto scale) => RDS proxy (pool connections) => RDS

Monitoring​

  • Performance Insights
    • a database performance tuning and monitoring feature that helps you quickly assess the load on your database
    • uses lightweight data collection methods that don't impact the performance of you application, and makes it easy to see which SQL statements are causing the load and why
  • Enhanced monitoring
    • you can monitor the operating system of your DB instance in real time
    • you can view all the system metrics and process information for your RDS DB instances on the console
    • main metrics: cpuUtilization, diskIO, loadAverageMinute, memory, network, processList, swap
    • difference between CloudWatch and Enhanced Monitoring
      • CloudWatch gathers metrics about CPU utilisation from the hypervisor for a DB instance
      • Enhanced Monitoring gathers its metrics from an agent on the DB instance
      • the hypervisor only does a small amount of work
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Last updated on by daniel.guo