Noticed your AWS Config bill creeping up month after month? Before you can fix it, you need to understand what you're paying for and how to pinpoint the exact resources driving those costs. Let's break it down.
Understanding the AWS Config Pricing Model
AWS Config charges you based on two primary dimensions:
1. Configuration Items Recorded
Think of AWS Config as a timeline database of configuration changes of each resource. Every time AWS Config records the state of a resource, that's a configuration item (CI). You're charged per CI recorded, per region. A configuration item is created whenever:
A new resource is created
An existing resource is modified
A resource is deleted
A relationship between resources changes
The pricing is tiered—the more CIs you record per month, the lower your per-unit cost becomes. But those volumes add up fast across multiple regions and accounts.
2. Config Rule Evaluations
Each time a Config rule evaluates your resources for compliance, you're charged. This happens:
When a rule is triggered by a configuration change (change-triggered rules)
On a scheduled basis (periodic rules)
When you manually re-evaluate a rule
Rule evaluations are also priced per evaluation, with tiered pricing based on volume.
What's NOT charged: Delivering configuration snapshots and history files to S3, or viewing data in the Config console.
The key takeaway? Your costs scale directly with how many resources you're tracking, how frequently they change, and how many rules you're running against them.
Identifying the Resources Causing Increased Costs
Now that you understand the pricing model, let's dig into the detective work. CloudWatch Metrics is your first stop for identifying cost drivers.
Using CloudWatch Metrics
AWS Config publishes several metrics to CloudWatch that help you track down resource-level activity:
Key Metrics to Monitor:
ConfigurationItemsRecorded - This is your primary cost indicator. It shows the total number of configuration items recorded in a region.
Cloud Watch Metrics - AWS Config number of configuration items
Set this up with a time-series view to spot trends
Compare month-over-month to identify sudden spikes
Break it down by checking the metric across all your active regions
ConfigRuleEvaluations - Tracks how many rule evaluations are running
High evaluation counts = higher costs
Look for rules that might be over-triggering
Using Advanced Queries to Pinpoint Changes in Specific Time Intervals
Once you've identified a cost spike in a particular timeframe, AWS Config's Advanced Query feature becomes your most powerful debugging tool. This SQL-like interface lets you query configuration items recorded during specific time intervals to see exactly what changed.
What is AWS Config Advanced Query?
Advanced Query allows you to use a SQL-like query language to search through your resource configurations and their history. Think of it as running SELECT statements against your entire AWS infrastructure's configuration database.
Why this matters for cost debugging: You can query specifically for resources that had configuration changes during the exact time period when your costs spiked, helping you identify the needle in the haystack.
Finding Resources Changed During Cost Spikes
Let's say your CloudWatch metrics show a spike on September 15, 2024, between 2 PM and 6 PM. Here's how to find the culprits:
SELECT
resourceType,
resourceId,
configurationItemCaptureTime,
configurationItemStatus
WHERE
configurationItemCaptureTime >= '2024-09-15T14:00:00Z'
AND configurationItemCaptureTime <= '2024-09-15T18:00:00Z'
ORDER BY
configurationItemCaptureTime DESCThis shows you every configuration item recorded during your cost spike window.
The combination of CloudWatch metrics for activity monitoring and Advanced Queries for granular investigation gives you complete visibility into your AWS Config costs. Start with the metrics, identify the patterns, drill down with queries, and then take targeted action to optimize.