You can run one or more DB Instances , and each DB Instance can support one or more databases or database schemas, depending on engine type.
Q: How many DB Instances can I run with Amazon RDS?
By default, customers are allowed to have up to a total of 40 Amazon RDS DB instances. Of those 40, up to 10 can be Oracle or SQL Server DB Instances under the"License Included"model. All 40 can be used for Amazon Aurora, MySQL, MariaDB, Oracle, SQL Server, or PostgreSQL under the "BYOL" model. If your application requires more DB Instances, you can request additional DB Instances viathisrequest form.
Q: How many databases or schemas can I run within a DB Instance?
RDS for Amazon Aurora: No limit imposed by software
RDS for MySQL: No limit imposed by software
RDS for MariaDB: No limit imposed by software
RDS for Oracle: 1 database per instance; no limit on number of schemas per database imposed by software
RDS for SQL Server: 30 databases per instance
Q: Will there always be reservations available for purchase?
Yes. Reserved Instances are purchased for the Region rather than for the Availability Zone. This means that even if capacity is limited in one Availability Zone, reservations can still be purchased in that Region and used in a different Availability Zone within that Region.
Q: How many Reserved Instances can I purchase?
You can purchase up to 40 Reserved DB Instances. If you wish to run more than 40 DB Instances, please complete theAmazon RDS DB Instance request form.
Q: Do I need to enable backups for my DB Instance or is it done automatically?
By default and at no additional charge, Amazon RDS enables automated backups of your DB Instance with a 1 day retention period. Free backup storage is limited to the size of your provisioned database and only applies to active DB Instances. For example, if you have 10GB-months of provisioned database storage, we will provide at most 10GB-months of backup storage at no additional charge.
What is a backup window and why do I need it? Is my database available during the backup window?
The preferred backup window is the user-defined period of time during which your DB Instance is backed up. Amazon RDS uses these periodic data backups in conjunction with your transaction logs to enable you to restore your DB Instance to any second during your retention period, up to the LatestRestorableTime (typically up to the last few minutes). During the backup window, storage I/O may be briefly suspended while the backup process initializes (typically under a few seconds) and you may experience a brief period of elevated latency. There is no I/O suspension for Multi-AZ DB deployments, since the backup is taken from the standby.
Q: What is a DB Subnet Group and why do I need one?
A DB Subnet Group is a collection of subnets that you may want to designate for your RDS DB Instances in a VPC. Each DB Subnet Group should have at least one subnet for every Availability Zone in a given Region. When creating a DB Instance in VPC, you will need to select a DB Subnet Group. Amazon RDS then uses that DB Subnet Group and your preferred Availability Zone to select a subnet and an IP address within that subnet. Amazon RDS creates and associates an Elastic Network Interface to your DB Instance with that IP address.
Q: Can I encrypt connections between my application and my DB Instance using SSL?
Yes, this option is currently supported for the MySQL, MariaDB, SQL Server, PostgreSQL, and Oracle engines.
Q: Can I encrypt data at rest on my Amazon RDS databases?
Amazon RDS supports encryption at rest for all database engines, using keys you manage usingAWS Key Management Service (KMS). On a database instance running with Amazon RDS encryption, data stored at rest in the underlying storage is encrypted, as are its automated backups, read replicas, and snapshots. Encryption and decryption are handled transparently. For more information about the use of KMS with Amazon RDS, see theAmazon RDS User's Guide.
Q: What does it mean to run a DB Instance as a Read Replica?
Read Replicas make it easy to take advantage of supported engines' built-in replication functionality to elastically scale out beyond the capacity constraints of a single DB Instance for read-heavy database workloads. You can create a Read Replica with a few clicks in the AWS Management Console or using the CreateDBInstanceReadReplica API. Once the Read Replica is created, database updates on the source DB Instance will be replicated using a supported engine's native, asynchronous replication. You can create multiple Read Replicas for a given source DB Instance and distribute your application’s read traffic amongst them. Since Read Replicas use supported engines' built-in replication, they are subject to its strengths and limitations. In particular, updates are applied to your Read Replica(s) after they occur on the source DB Instance, and replication lag can vary significantly. Read Replicas can be associated with Multi-AZ deployments to gain read scaling benefits in addition to the enhanced database write availability and data durability provided byMulti-AZ deployments.
Q: When would I want to consider using an Amazon RDS Read Replica?
There are a variety of scenarios where deploying one or more Read Replicas for a given source DB Instance may make sense. Common reasons for deploying a Read Replica include:
Q: Do I need to enable automatic backups on my DB Instance before I can create read replicas?
Yes. Enable automatic backups on your DB Instance before adding Read Replicas, by setting the backup retention period to a value other than 0. Backups must remain enabled for Read Replicas to work.