Let’s get a quick overview of Multi-AZ vs Multi-Region vs Read replicas for Amazon RDS from an AWS certification perspective.
You will learn
- What are Multi-AZ Deployments?
- What are Read replicas?
- How do you choose between Multi-AZ deployments vs Multi-Region vs Same-Region Read replicas?
Table of Contents
- Multi-AZ Deployments
- Read Replicas
- RDS Multi-AZ vs Multi-Region vs Read replicas - Certification Questions and Scenarios
Multi-AZ Deployments
- Standby created in a different AZ
- Synchronous replication (strong consistency)
- Enhances durability, availability and fault tolerance of your database
- Multi-AZ makes maintenance easy
- Perform maintenance (patches) on standby
- Promote standby to primary
- Perform maintenance on (old) primary
- Avoid I/O suspension when data is backed up (snapshots are taken from standby)
- No downtime when database is converted to Multi AZ
- Increased latency until standby is ready
- Not allowed to connect to standby database directly
- For example: Standby CANNOT be used to serve read traffic
- Standby increases availability but does not improve scalability
- Automatic failover to standby if master has problems (compute, storage or networking)
- CNAME record flipped to standby
- Database performance issues (long running queries or deadlocks) will NOT cause a failover
- (Good Practice) Use DNS name of database in applications configuration
Read Replicas
- Support read-heavy database workloads - reporting and data warehousing
- Can be in same or different AZ or different Region
- Your apps can connect to them
- Create read replica(s) of a read replica
- Uses asynchronous replication
- Provides eventual consistency (from replica)
- For higher consistency, read from master
- Need to be explicitly deleted (Not deleted when database is deleted)
- (Mandatory) Enable automatic backups before you can create read replicas
- Set Backup Retention period to a value other than 0
- Reduce replication lag by using better compute and storage resources
- Maximum no of read replicas:
- MySQL, MariaDB, PostgreSQL, and Oracle - 5
- Aurora - 15
- SQL Server does not support read replicas
RDS Multi-AZ vs Multi-Region vs Read replicas - Certification Questions and Scenarios
| Feature | Multi-AZ deployments | Multi-Region Read Replicas | Multi-AZ Read replicas |
|---|---|---|---|
| Main purpose | High availability | Disaster recovery and local performance | Scalability |
| Replication | Synchronous (except for Aurora - Asynchronous) | Asynchronous | Asynchronous |
| Active | Only master (For Aurora - all) | All read replicas | All read replicas |