· Alexey Eremin · 1 min read
Less frequent recording with AWS Config can cost more.
After the EKS-to-ECS migration, our AWS Config costs began to rise. I thought: switching from continuous to daily recording should cut costs, given how many records our ECS network interfaces generate. And it turns out Control Tower resets your recording configuration. Then I heard about FivexL’s terraform-aws-control-tower-config-recorder module, which automatically reapplies your recording settings, and I used it to apply the configuration.
When I saw a higher bill after the switch, I was surprised.
Turns out that a daily record costs four times as much as a continuous record. Whether daily or continuous recording is cheaper depends on how many records each produces, which varies by resource.
A simplified example over one day:
One ECS network interface changes 10 times:
Continuous: 10 records × $0.003 = $0.030
Daily: 1 record × $0.012 = $0.012
Daily is 60% cheaper because it records only the resource’s latest state, rather than each intermediate change.
One security group changes once:
Continuous: 1 record × $0.003 = $0.003
Daily: 1 record × $0.012 = $0.012
Daily costs four times as much because there are no repeated changes to combine.
At these prices, one daily record must replace more than four continuous records to save money. Four is break-even.
https://github.com/fivexl/terraform-aws-control-tower-config-recorder