Amazon Relational Database Service is a distributed relational database service by Amazon Web Services. It is a web service running "in the cloud" designed to simplify the setup, operation, and scaling of a relational database for use in applications. Administration processes like patching the database software, backing up databases and enabling point-in-time recovery are managed automatically. Scaling storage and compute resources can be performed by a single API call as AWS does not offer an ssh connection to RDS instances.
New database instances can be launched from the AWS Management Console or using the Amazon RDS APIs. Amazon RDS offers different features to support different use cases. Some of the major features are:
Multi-Availability Zone (AZ) deployment
In May 2010 Amazon announced Multi-Availability Zone deployment support. Amazon RDS Multi-Availability Zone allows users to automatically provision and maintain a synchronous physical or logical "standby" replica, depending on database engine, in a different Availability Zone. Multi-AZ database instance can be developed at creation time or modified to run as a Multi-AZ deployment later. Multi-AZ deployments aim to provide enhanced availability and data durability for MySQL, MariaDB, Oracle, PostgreSQL and SQL Server instances and are targeted for production environments. In the event of planned database maintenance or unplanned service disruption, Amazon RDS automatically fails over to the up-to-date standby, allowing database operations to resume without administrative intervention. Multi-AZ RDS instances are optional and have a cost associated with them. When creating a RDS instance, the user is asked if they would like to use a Multi-AZ RDS instance. In Multi-AZ RDS deployments backups are done in the standby instance so I/O activity is not suspended any time but you may experience elevated latencies for a few minutes during backups.
Read replicas
Read replicas allow different uses case such as to scale in for read-heavy database workloads. Available are up to five replicas for MySQL, MariaDB, and PostgreSQL instances use the native, asynchronous replication functionality of their respective database engines, have no backups configured by default and are accessible and can be used for read scaling. MySQL and MariaDB read replicas can be made writeable again since October 2012; PostgreSQL read replicas do not support it. Replicas are done at database server level and do not support replication at database instance or table level.
for Amazon RDS are available from the AWS Management Console or the Amazon CloudWatch API. In December 2015, Amazon announced an optional enhanced monitoring feature that provides an expanded set of metrics for the MySQL, MariaDB, and Aurora database engines.
RDS costs
Amazon RDS instances are priced very similarly to Amazon Elastic Compute Cloud. RDS is charged per hour and comes in two packages: On-Demand DB Instances and Reserved DB Instances. On-Demand Instances are at an ongoing hourly usage rate. Reserved DB Instances require an up-front, one-time fee and in turn provide a discount on the hourly usage charge for that instance. Apart from the hourly cost of running the RDS instance, users are charged for the amount of storage provisioned, data transfers and input and output operations performed. AWS have introduced Provisioned Input and Output Operations, in which the user can define how many IO per second are required by their application. IOPS can contribute significantly to the total cost of running the RDS instance. As part of the AWS Free Tier, the Amazon RDS Free Tier helps new AWS customers get started with a managed database service in the cloud for free. You can use the Amazon RDS Free Tier to develop new applications, test existing applications, or simply gain hands-on experience with Amazon RDS.
Automatic backups
Amazon RDS creates and saves automated backups of RDS DB instances. The first snapshot of a DB instance contains the data for the full DB instance and subsequent snapshots are incremental, maximum retention period is 35 days. In Multi-AZ RDS deployments backups are done in the standby instance so I/O activity is not suspended for any amount of time but you may experience elevated latencies for a few minutes during backups.
Operation
Database instances can be managed from the AWS Management Console, using the Amazon RDS APIs and using aws cli. Since 1 June 2017, you can stop AWS RDS instances from AWS Management Console or AWS CLI for 7 days at a time. After 7 days, it will be automatically started, and since September 2018 RDS instances can be protected from accidental deletion. Increase DB space is supported, but not decrease allocated space. Additionally there is at least a six-hour period where new allocation cannot be done.
