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RDS

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  • Traditional relational databases that include tables, rows, fields
  • On-Line Transaction Processing (OLTP) type DB
  • You can copy a snapshot to another region if you want to have your database available in another region
  • You scale your DB by taking a snapshot and doing a restore to a larger sized tier
  • RDS maximum size for a MS SQL Server DB with SQL Server Express Edition is 10GB per DB
  • Supported RDS Platforms:
    • MS SQL Server
    • Oracle
    • MySQL Server
    • PostgreSQL
    • Aurora
    • MariaDB
  • When a backup is restored, the restore will always be a new RDS instance, with a new DNS name
  • Backup types:
    • Automated backups
      • Allows you to recover your database to any point in time within a retention period
      • Retention periods can be between 1 and 35 days
      • Takes a full daily snapshot and will also store transaction logs through the day
      • When you do a recovery, AWS will choose the most recent daily backup and then apply transaction logs
      • Allows you to do a point in time recover down to a second within the retention period
      • Enabled by default
      • Backup data is stored in S3
      • You get free storage space equal to the size of your database.
      • Taken within a defined window
      • During the backup, storage I/0 may be suspended and you may experience extended latency
    • Database snapshots
      • User initiated from the console
      • Stored even after you delete the original RDS instance unlike automatic backups
  • Encryption:
    • Encryption at rest is supported for MySQL, Oracle, SQL Server, PostgreSQL, and MariaDB
    • Encryption is done using the AWS Key Management Service (KMS)
    • Once your RDS instance is encrypted the data stored at rest in the underlaying storage is encrypted, as are its automated backups, read replicas and snapshots
    • To use RDS encryption, create a new DB instance with encryption enabled and migrate your data to it
    • Encrypting an existing DB instance is not supported

RDS And Multi-AZ Failover

  • Allows you to have an exact copy of your production database in another AZ
  • AWS handles the replication for you, so when your prod database is written to, the write will automatically be synchronized to the stand-by DB
  • In the event of DB maintenance, instance failure or AZ failure, RDS will automatically fail-over to the standby so that database operations can resume quickly without Admin intervention.
  • In a fail-over scenario, the same DNS name is used to connect to the secondary instance, There is no need to reconfigure your application
  • Multi AZ configurations are used for HA/DR only, and is not used for improving performance
  • To scale for performance you need to set up read replicas
  • Available for SQL Server, Oracle, MySQL, PostGreSQL, and Aurora

RDS & Using Read Replicas

  • Uses asynchronous replication, from the primary instance to other instances that can be read from
  • You can have up to 5 read replicas of your main database
  • Allow you to have a read only copy of your prod database
  • Used primarily for very read-heavy database workloads
  • SQL Server and Oracle are not supported
  • Used for scaling not DR
  • Must have automatic backups setup
  • You can have read replicas of read replicas (but could incur latency as its daisy chained)
  • Each read replica will have its own DNS endpoint
  • You cannot have read replicas that have Multi-AZ
  • You can create read replicas of Multi-AZ source databases however
  • Read Replicas can be promoted to be their own databases, however this breaks replication
  • Read Replicas in a second region for MySQL and MariaDB, not for PostgreSQL
  • Read Replicas can be bigger than the primary source DB from a resource perspective
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