I've been reading some EBS docs
and they are talking about "I/O credit balance"
How can I view my current (or historical) credit balance?
Each volume receives an initial I/O credit balance of 5,400,000 I/O
credits, which is enough to sustain the maximum burst performance of
3,000 IOPS for 30 minutes. This initial credit balance is designed to
provide a fast initial boot cycle for boot volumes and to provide a
good bootstrapping experience for other applications. Volumes earn I/O
credits every second at a base performance rate of 3 IOPS per GiB of
volume size. For example, a 100 GiB General Purpose (SSD) volume has a
base performance of 300 IOPS.
Best Answer
AWS recently added Burst Balance metric to monitor your balance, the metrics is 0-100% and says how far is your volume from 5.4 million.
The AWS Blog post about it
This is available for EC2 gp2 Volumes as well as RDS gp2 Volumes.
To view it for EC2 EBS Volumes, go to Cloudwatch -> Metrics -> EBS -> BurstBalance.
To view it for RDS Instances, go to Cloudwatch -> Metrics -> RDS -> BurstBalance.