A relational database is one that stores data in tables. The relationship between each data and searching through those relationships is relatively easy. The relationship between tables and field type is called a schema. for a relational database, the schema must be clearly defined.

Or, we can simply say that Relational Databases show the relationship between tables is related to each other. In this database, each field is filled, you can not leave an empty field. It is best suitable for OLTP (Online Transaction Processing).

Amazon RDS(Relational Database Service)

Amazon RDS is the “managed” relational database service offered as a web service by amazon. it makes it easy to set-up and operate a relational database in the cloud. It provides a very cost-effective way to use the industry’s leading RDBMS software as a managed service. because of this web service from amazon AWS, you do not have to buy any server or install any database software in it. you just subscribe to the was RDS web service and start using it. It can do various automated tasks, such as doing security patches, backups, etc.

AWS fully Managed RDS Service Where AWS is Responsible for

• Security and patching 
• Automated backup
• Multi-AZ (For Disaster Recovery)
• Read Replica (For performance)
• Software updates for the DB engine
• By default, Every database has a weekly maintenance window(max. 1-35 days)

Automated Backups 

Automated backups are enabled by default. The backup data is store in an S3 bucket. Backups are taken within a defined window. During the backup window, storage I/O may be suspended while your data is being backed up and you may experience elevated latency.
Database Snapshots: DB snapshots are done manually. They are stored even after you delete the original RDS instance.

Multi-AZ in RDS

Multi-AZ allows you to have an exact copy of your production database in another availability zone. AWS handles the replication for you, so when your production database is written, this will automatically be synchronized to the standby database.

• You can select the Multi-AZ(availability zone) option during the RDS DB instance launch.
• RDS service creates a standby instance in a different AZ in the same region and configures “Synchronous Replication” between the primary and standby DB.
• You can not read/write to the standby RDS DB instance.
• You can not select which AZ in the region will be chosen to create the standby DB instance. 
• You can however view which AZ is selected after the standby is created.
• AWS recommends the use of a provisioned IOPS instance for multi-AZ RDS instance.

Read Replicas

Read replicas allow you to have a read-only copy of your production database. this is achieved by using asynchronous replication from the primary RDS instance to the read replica. you use read replicas primarily for every read-heavy database workload. Read replica is used for scaling not for data recovery. you can have up to 5 read replica copy of any database. You can have a read replica in a second region. 

License Options for RDS

There are basically two license option for RDS

1. BYOL: Bring your own online license(user your license)
2. License Included: AWS provides a license. 

RDS Instance Storage in AWS

Amazon RDS uses EBS volumes (not instance store) for DB and log storage. 

• General Purpose: use for moderate i/o requirement.
• Provisional IOPS: Use for high-performance OLTP workloads.

RDS Limits in AWS

You can create up to 40DB instances per account.

AWS Templates Available in RDS

1. Production: These templates use for production with high availability and consistent performance of any application.
2. Dev/Test: These templates use for development or testing applications outside of production.
3. Free-Tier: Use the free tier template to develop a new application, test the existing app, or gain hands-on experience.