Relational Database Service (RDS)

  1. RDS is AWS managed relational db service. Database will run in EC2 instance withing your VPC/Subnet but you can’t SSH or have root access
  2. Two types of backups are supported
    1. Automatic Backups
      1. Enabled by default
      2. Backup data is stored in S3 (you get free S3 storage allowance equal to the size of your RDS db)
      3. Daily snapshots + transaction logs
      4. AB’s let you recover at any point of time within a retention period
      5. Retention period can be 1 day to 35 days
      6. Backups are taken at a specified window of time
      7. During the backup time the latency may be higher than normal so choose a backup window time which is least in demand for your services
    2. Snapshots
      1. Snapshots are manual
      2. Initiated by the admins
      3. Unlike backups, the snapshots are available even after you deleted your RDS instances
      4. When you restore a snapshot it will create a new RDS instance with a new endpoint.
  3. Encryption
    1. Encryption at rest is done thru AWS KMS
    2. supported for MySQL, Oracle, MariaDb, SQL ServerĀ  and PostGreSQL
    3. Existing un-encrypted db can’t be encrypted. You need create a new encrypted RDS instance and migrate to it
    4. All snapshots, automatic backups will be encrypted as well
  4. Multi AZ deployment for high availability
    1. Synchronously replicated
    2. Automatic fail over (dns endpoint remains same. No need to point to the secondary db)
    3. Disaster Recovery (DR) purpose only. Not for performance. Use read replicas for scalability and performance enhancements
  5. Read Replicas
    1. They are different from multi Availability Zone deployment
    2. Asynchronous replication (NOT Synchronous)
    3. Creates exact copy of master db
    4. If multi AZ is enabled, the RR when created uses secondary db to create the initial snapshot thus avoiding 1 min slowdown time which would otherwise happen
    5. Read replicas have separate end points which can be directly used by EC2 instances running applications (connection strings)
    6. Read replicas can have read replicas
    7. MySQL, Maria Db and PostgreSQL support 5 Read Replicas. Aurora supports upto 15 read replicas.
    8. RRs can be a different region/AZ for MySQL
    9. RRs can be promoted to be master dbs. Once promoted, the RR link will be lost and the promoted instance will act as an independent master db
    10. RRs are Read only. Can’t write to RRs
    11. Scaling up is a manual process unlike in DynamoDB where scaling can take place with push button
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