Managing performance and scaling for Amazon Aurora MySQL

Scaling Aurora MySQL DB instances

You can scale Aurora MySQL DB instances in two ways, instance scaling and read scaling. For more information about read scaling, see Read scaling.

You can scale your Aurora MySQL DB cluster by modifying the DB instance class for each DB instance in the DB cluster. Aurora MySQL supports several DB instance classes optimized for Aurora. Don't use db.t2 or db.t3 instance classes for larger Aurora clusters of size greater than 40 TB. For the specifications of the DB instance classes supported by Aurora MySQL, see DB instance classes.

Maximum connections to an Aurora MySQL DB instance

The maximum number of connections allowed to an Aurora MySQL DB instance is determined by the max_connections parameter in the instance-level parameter group for the DB instance.

The following table lists the resulting default value of max_connections for each DB instance class available to Aurora MySQL. You can increase the maximum number of connections to your Aurora MySQL DB instance by scaling the instance up to a DB instance class with more memory, or by setting a larger value for the max_connections parameter in the DB parameter group for your instance, up to 16,000.

Instance class	max_connections default value
db.t2.small	45
db.t2.medium	90
db.t3.small	45
db.t3.medium	90
db.r3.large	1000
db.r3.xlarge	2000
db.r3.2xlarge	3000
db.r3.4xlarge	4000
db.r3.8xlarge	5000
db.r4.large	1000
db.r4.xlarge	2000
db.r4.2xlarge	3000
db.r4.4xlarge	4000
db.r4.8xlarge	5000
db.r4.16xlarge	6000
db.r5.large	1000
db.r5.xlarge	2000
db.r5.2xlarge	3000
db.r5.4xlarge	4000
db.r5.8xlarge	5000
db.r5.12xlarge	6000
db.r5.16xlarge	6000
db.r5.24xlarge	7000

If you create a new parameter group to customize your own default for the connection limit, you'll see that the default connection limit is derived using a formula based on the DBInstanceClassMemory value. As shown in the preceding table, the formula produces connection limits that increase by 1000 as the memory doubles between progressively larger R3, R4, and R5 instances, and by 45 for different memory sizes of T2 and T3 instances.

The DBInstanceClassMemory value represents the memory capacity, in bytes, available for the DB instance. It's a number that Aurora computes internally and isn't directly available for you to query. Aurora reserves some memory in each DB instance for the Aurora management components. This adjustment to the available memory produces a lower max_connections value than if the formula used the full memory for the associated DB instance class.

Aurora MySQL and RDS MySQL DB instances have different amounts of memory overhead. Therefore, the max_connections value can be different for Aurora MySQL and RDS MySQL DB instances that use the same instance class. The values in the table only apply to Aurora MySQL DB instances.

The much lower connectivity limits for T2 and T3 instances are because with Aurora, those instance classes are intended only for development and test scenarios, not for production workloads.

The default connection limits are tuned for systems that use the default values for other major memory consumers, such as the buffer pool and query cache. If you change those other settings for your cluster, consider adjusting the connection limit to account for the increase or decrease in available memory on the DB instances.