You can think of a RDS DB Instance as a database environment in the cloud with the compute and storage resources you specify.
You can create and delete DB Instances, define/refine infrastructure attributes of your DB Instance(s), and control access and security via the AWS Management Console, Amazon RDS APIs, and Command Line Tools.
Multiple MySQL databases or SQL Server databases (up to 30) or Oracle database schemas can be created on a given DB Instance.
For optional Multi-AZ deployments (currently supported for MySQL and Oracle database engines), Amazon RDS also manages synchronous data replication across Availability Zones and automatic failover.
By default, customers are allowed to have up to a total of 20 Amazon RDS DB instances.
RDS cannot remove storage once it has been allocated. The only way to reduce the amount of storage allocated to a DB Instance is to dump the data out of the DB Instance, create a new DB Instance with less storage space, and load the data into the new DB Instance.
Unlike Multi-AZ deployments, Read Replicas use MySQL’s built-in replication and are subject to its strengths and limitations.This means recent database updates made to a standard (non Multi-AZ) source DB Instance may not be present on associated Read Replicas in the event of an unplanned outage on the source DB Instance. As such, Read Replicas do not offer the same data durability benefits as Multi-AZ deployments. While Read Replicas can provide some read availability benefits, they and are not designed to improve write availability. Read Replicas are currently supported for Amazon RDS for MySQL. They can also be used for serving read traffic when the primary database is unavailable.
The read replica mechanism uses MySQL’s native, asynchronous replication. This means replicas might be lagging behind the master as they try to catch up with writes. The interesting thing about this is that multi-AZ RDS instances apparently use another,_ proprietary type_ of synchronous replication.
A Read Replica will stay active and continue accepting read traffic even after its corresponding source DB Instance has been deleted. If you desire to delete the Read Replica in addition to the source DB Instance, you must explicitly delete the Read Replica using the DeleteDBInstance API or AWS Management Console.
By default and at no additional charge, Amazon RDS enables automated backups of your DB Instance with a 1 day retention period.
During the backup window, storage I/O may be suspended while your data is being backed up. This I/O suspension typically lasts a few minutes at most. This I/O suspension is avoided with Multi-AZ DB deployments, since the backup is taken from the standby.
Amazon RDS DB snapshots and automated backups are stored in S3.
If you desire to turn off automated backups altogether, you can do so by setting the retention period to 0 (not recommended).
When you delete a DB Instance, you have the ability to specify whether a final DB Snapshot is created upon deletion, which enables a DB Snapshot restore of the deleted database instance at a later date. All previously created DB Snapshots of your DB Instance will be retained and billed at $0.15 per GB-month, unless you choose to delete them.
Amazon RDS does not currently provide access to the binary logs for your Database Instance.
You are not charged for the data transfer incurred in replicating data between your source DB Instance and Read Replica. Billing for a Read Replica begins as soon as the Read Replica has been successfully created (i.e. when status is listed as “active”). The Read Replica will continue being billed at standard Amazon RDS DB Instance hour rates until you issue a command to delete it.
The default storage engine with RDS is InnoDB, but you are free to choose another, like the popular MyISAM. It is important to realize that read replicas on nontransactional storage engines (like MyISAM) require you to freeze your databases, as the consistency cannot be guaranteed when snapshotting. But if you use InnoDB, you are safe, and the only thing you have to do is fire up a new read replica.
RDS storage is independent of RDS instance classes. Every class can have from 5 GB to 1 TB of storage associated. Scaling up the storage is easy, and you can do it using the Console. It does require a reboot. On the other hand, scaling down the storage is impossible.
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