Managing AWS Config Costs: Recording Changes to SNS Topic Policies

If you are an AWS administrator or a security enthusiast,you know that visibility is everything. Enabling AWS Config to track changes to your SNS (Simple Notification Service) Topics is a best practice for security and compliance. However, a common question arises: Will recording these changes significantly increase your AWS Config costs?

SNS Config Change

• 1. The Cost Breakdown: Configuration Items (CIs)
  • Cost Scenarios
• 2. When Do AWS Config Costs Spike?
  • A. Infrastructure as Code (IaC) “Drift”
  • B. Relationship & IAM Changes
  • C. The “Global Resource” Trap
• 3. Recommendations for Your Setup
• How to Monitor Your Current Usage

The short answer is: Yes, but typically the increase is negligible—unless your environment is highly automated or you are making hundreds of changes daily. Here is a deep dive into how the billing works and how to optimize your setup.

1. The Cost Breakdown: Configuration Items (CIs)

AWS Config pricing is primarily driven by Configuration Items (CIs). A CI is generated every time a change is detected in a resource, such as updating an SNS access policy, adding a tag, or modifying attributes.

The recording mode you choose determines how you are billed:

Recording Mode	Cost per CI	How it Works
Continuous	$0.003	Charged every time you save a policy change.
Periodic (Daily)	$0.012	Charged once per 24 hours, regardless of change frequency.

Cost Scenarios

• 1 Update/Day: Continuous costs $0.003, while Periodic costs $0.012. Continuous is cheaper.
• 10 Updates/Day: Continuous costs $0.030, while Periodic remains capped at $0.012. Periodic is cheaper.

2. When Do AWS Config Costs Spike?

While recording a static SNS topic usually costs pennies per month, there are three scenarios where costs can unexpectedly climb:

A. Infrastructure as Code (IaC) “Drift”

If you use Terraform or AWS CloudFormation scripts that “touch” or re-apply attributes to your SNS topics every time a pipeline runs, you trigger a new CI. In a CI/CD environment where deployments happen hourly, these micro-costs add up.

B. Relationship & IAM Changes

AWS Config doesn’t just record the topic; it records changes to related resources. If an IAM role attached to the SNS topic is modified, it can sometimes trigger multiple CIs across the resource dependency chain.

C. The “Global Resource” Trap

If you are tracking IAM policies (which are global), be extremely careful. If you enable “Record Global Resources” in every AWS Region, a single change to an IAM policy will trigger a $0.003 charge in every single region where Config is active.

3. Recommendations for Your Setup

To balance security with cost-efficiency, consider this tiered strategy:

1. Production (Continuous): Keep Continuous Recording enabled. The $0.003 fee is a small price to pay for a real-time audit trail of who changed a security policy.
2. Dev/Test (Periodic): If you have a lab or sandbox account where you are constantly testing automation scripts, switch to Periodic Recording. This caps your daily cost at $0.012 per resource, protecting you from billing spikes caused by automation loops.
3. Regional Scoping: Ensure global resources (like IAM) are only recorded in one primary region to avoid redundant charges.

How to Monitor Your Current Usage

Before you see your next bill, you can proactively check how many CIs your SNS topics are generating.

Pro Tip: You can use the AWS CLI to retrieve the number of configuration items recorded per month. This helps you identify “noisy” resources that are driving up your costs.

Would you like me to provide a specific AWS CLI command to help you estimate your next bill by counting the CIs generated by your SNS topics last month?