AWS Relational Database Service (RDS) gives users the option to generate Read Replicas to offload read traffic from your database’s primary instance. The most apparent beneficiaries of Read Replicas are applications with heavy database read traffic. You can create up to five Read Replicas for each primary DB instance, and they can each have separate Availability Zones.
One of the main reasons for using Read Replicas is to increase database availability. By segregating your database read traffic from write traffic through Read Replicas, you can ensure high availability and read scalability for your applications.
When to Use Read Replicas
You should consider implementing Read Replicas in the following situations:
- Scale Out Read Capacity: If your application encounters heavy database read traffic, you may face performance issues due to the high volume of queries being executed on your primary DB instance. In this case, implementing Read Replicas can help alleviate the load from your primary database by distributing the read traffic among multiple replicas.
- Reporting and Analytics: Many enterprises have regular reporting and analytics requirements. These processes often involve complex queries and substantial data reading, which can impact the performance of your primary database. Implementing Read Replicas for these tasks can help ensure your primary instance remains highly available for transactional processing.
- Disaster Recovery: In case of a failure in the primary DB instance, you can promote a Read Replica to become the new primary database. This ensures business continuity without significant downtime.
Comparing Primary DB Instances and Read Replicas
| Primary DB Instances | Read Replicas | |
|---|---|---|
| Role | Handling both read and write operations | Handling read operations only |
| Limit | No limit | Up to 5 per primary DB instance |
| Use cases | Transaction processing | Scale read capacity, Reporting and Analytics, Disaster recovery |
How to Create a Read Replica
Creating a Read Replica can be achieved through the AWS Management Console, the AWS CLI, or RDS API. For instance, in the AWS Management Console:
- Navigate to the “RDS” service
- On the navigation pane, select “Databases”
- Select the DB instance which you want to create a read replica of
- Choose “Actions”, then select “Create read replica”
Thereafter, you can specify the details for your Read Replica accordingly.
Choosing the correct time to use Read Replicas is important to ensure the smooth operation of your applications and services. By implementing Read Replicas when suitable, you can enhance the performance, scalability, and availability of your database operations. This fundamental knowledge is invaluable for any aspiring AWS Certified Solutions Architect – Associate.
Practice Test
True or False: Read replicas in AWS are primarily used to increase write capacity of your database.
- True
- False
Answer: False
Explanation: While read replicas do increase capacity, they primarily increase read capacity, not write capacity. They are used to offload the read traffic from the primary database.
Which of the following scenarios are suitable for using read replicas? (Multiple Select)
- A. When you need to handle high-volume application read traffic.
- B. When you require data locality due to compliance or latency issues.
- C. When you want to increase write capacity.
- D. When you want to isolate analytical reporting queries from operational workloads.
Answer: A, B, D
Explanation: Read replicas are suitable when you need to handle high-volume application read traffic, require data locality due to compliance or latency issues, and want to isolate analytical reporting queries from operational workload. They do not increase write capacity.
True or False: AWS RDS read replicas support all kinds of database engines.
- True
- False
Answer: False
Explanation: AWS RDS supports read replicas for MySQL, MariaDB, PostgreSQL, and Amazon Aurora.
True or False: You can have a maximum of five read replicas for each primary DB instance.
- True
- False
Answer: True
Explanation: Yes, you can have up to five read replicas for each DB instance.
True or False: Read replicas provide the same data protection as multi-AZ deployments.
- True
- False
Answer: False
Explanation: While read replicas distribute traffic and enhance performance, they do not have the same failover capabilities as multi-AZ deployments.
When should you consider upgrading from read replicas to multi-AZ deployments? (Single select)
- A. When you need to offload read traffic.
- B. When you need data duplication for analytics.
- C. When you need an automatic failover mechanism.
- D. When you want to reduce costs.
Answer: C
Explanation: Multi-AZ deployments, unlike read replicas, provide an automatic failover mechanism by maintaining a standby copy of your data.
When are read replicas preferred over using DynamoDB for your AWS architecture? (Single select)
- A. When your application requires extensive write capacity.
- B. When your use case involves frequent querying of non-relational data.
- C. When you require data locality due to GDPR or HIPAA regulations.
- D. When cost-effectiveness is your primary concern.
Answer: C
Explanation: Read replicas can provide localized reading of database. It is ideal when compliance issues like GDPR or HIPAA require data locality.
True or False: AWS Aurora supports up to 15 read replicas with millisecond replica lag.
- True
- False
Answer: True
Explanation: The Amazon Aurora database engine supports up to 15 read replicas with no lag, as the data is replicated to all of them simultaneously.
Can a read replica in AWS RDS be promoted to a standalone database instance?
- True
- False
Answer: True
Explanation: If needed, a read replica can be promoted to a standalone database instance. However, its replication from the source database will stop.
What is the purpose of creating read replicas in a different geographical region? (Single select)
- A. To reduce read latency for users in that region.
- B. To serve as a backup for disaster recovery.
- C. Both A and B.
- D. Neither A nor B.
Answer: C
Explanation: Read replicas in different regions can both improve performance for end-users by reducing read latency and serve as a disaster recovery solution.
Interview Questions
What is a read replica in the AWS environment?
A read replica is a copy of the master DB instance. It enables the offloading of read traffic from the master DB instance and helps to save costs on high throughput workloads.
When should one use read replicas in AWS?
Read replicas are commonly used when an application has more read traffic than write traffic. They can also be used for reporting, data warehousing, and read-heavy database workloads.
Can read replicas enhance the performance of AWS RDS?
Yes, read replicas can significantly improve the read performance of AWS RDS by offloading read traffic from the primary database instance.
What is one of the main benefits of using read replicas in AWS?
One of the main benefits of using read replicas is the ability to offload read traffic from the primary DB instance, lowering the load on the primary and improving overall database performance.
How many read replicas can you create in AWS RDS?
You can create up to five read replicas for an Amazon RDS DB instance.
Can you create read replicas of read replicas in AWS RDS?
Yes, you can create a second-tier read replica from an existing read replica. However, any latency inherited from the primary replica will be added to the second-tier replica.
Can you write to a read replica in AWS RDS?
No, you can’t write to a read replica. They are read-only copies of the master database.
Can a read replica be promoted to a master DB instance in AWS RDS?
Yes, a read replica can be promoted to become a standalone DB instance that accepts both read and write operations.
Can you have a read replica in a region different from the primary DB instance in AWS RDS?
Yes, you can have a read replica in a different region from the primary DB instance. This is useful for disaster recovery, migration, or to serve global users.
Does using read replicas impact the performance of the master DB instance in AWS RDS?
There may be a small impact, as replicas are updated with changes from the master DB. However, by offloading read operations to the replicas, the overall performance of the master DB can improve.
What DB engines support read replicas in AWS RDS?
Amazon RDS supports read replicas for the MySQL, MariaDB, PostgreSQL, Oracle, and SQL Server database engines.
Do read replicas support Multi-AZ deployments?
No, read replicas do not support Multi-AZ deployments. However, the source instance of the read replica can be a Multi-AZ deployment.
How does AWS ensure data consistency between the master DB instance and its read replicas in RDS?
AWS uses asynchronous replication for data consistency. Changes to the master DB instance are replicated on the read replica.
Are read replicas used for automatic failover in AWS RDS?
No, read replicas are not used for automatic failover. For automatic failover, you should implement Multi-AZ deployments.
Can I use read replicas with Amazon Aurora?
Yes, Amazon Aurora allows up to 15 low-latency read replicas, which support both single-master and multi-master replication groups.
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