RDSDiskAutoScalingLimit #

Meaning #

Alert is triggered when an RDS instance reaches its maximum disk auto-scaling limit.

Impact #

The instance’s storage can no longer be increased automatically by AWS. This can lead to disk space saturation and instance shutdown.

Diagnosis #

1. Get storage auto-scaling limit

   aws rds describe-db-instances --db-instance-identifier <rds_instance_identifier> --query '{used: DBInstances[0].AllocatedStorage, max: DBInstances[0].MaxAllocatedStorage}'
   

2. Examine the disk growth trend to estimate the new limit to be applied

Mitigation #

1. Increase disk autoscaling limit (at least by 10% to allow RDS autoscaling)

   AWS RDS limitations

   • Minimal disk increase is 10%

   • You can’t make further storage modifications for either six (6) hours or until storage optimization has completed on the instance, whichever is longer.

   • Storage optimization can take several hours

   • Storage can’t be reclaimed

   See more on AWS documentation

   AWS recommendation

   We recommend setting it to at least 26% more to avoid receiving an event notification that the storage size is approaching the maximum storage threshold. Source

   aws rds modify-db-instance \
   --db-instance-identifier  \
   --max-allocated-storage <new_storage_limit_minimum_10%_increase> \
   --apply-immediately \
   

2. Check that the new auto-scaling limit is applied

Additional resources #

FinOps best practices

You should set up and review RDS event notifications for automatic disk scaling operations (RDS-EVENT-0217), to ensure that storage costs reflect your business activity.

• https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/USER_PIOPS.StorageTypes.html