Hi everyone. I'm still pretty new to using Terraform for AWS, but I've been trying to learn about cost management and security.
I just built a simple script to estimate monthly CSPM costs based purely on the number of assets (like EC2 instances, S3 buckets, IAM roles). I was shocked. 😳 For my small test VPC with ~50 resources, the quotes from a few big vendors were way higher than I expected.
My script is basic, but here's the core logic:
```python
# Simplified calculation
def estimate_cost(asset_count, price_per_asset):
monthly_cost = asset_count * price_per_asset
return monthly_cost * 1.2 # adding a rough overhead factor
```
Has anyone else done this kind of comparison? I'm worried my basic Terraform setups will become too expensive to monitor properly. Are there more cost-effective approaches for small to medium AWS accounts? Maybe focusing on specific high-risk resources first?
Your script is a good starting point, but the core assumption that CSPM vendors charge a simple linear cost per asset is often incorrect. Most pricing models are tiered and also factor in data points scanned per month, the number of policies evaluated, and the inclusion of features like compliance reporting or drift detection. A simple EC2 instance might count as one asset, but a single S3 bucket could generate hundreds of cost events if it's monitored for object-level security findings.
For a small AWS account, you're right to be concerned about cost. I'd recommend a pragmatic, phased approach instead of a full-blown CSPM suite immediately. You can get significant value by first instrumenting your Terraform with:
1. **Infracost** for direct IaC cost estimation.
2. **AWS Config rules** targeted only at your most critical resources (e.g., S3 buckets with public access, IAM password policy). The managed config rules cost per rule per region per month, not per asset.
3. **Custom scripts** that query AWS Security Hub findings or Cost Explorer APIs on a scheduled basis. This is more work but keeps costs predictable.
The surprising quotes you're seeing likely include the overhead for a platform designed for enterprises with thousands of accounts. You don't need that scale yet. Start with focused, high-risk coverage and expand as your infrastructure grows.
Your shock is justified, and the linear calculation is a useful starting point. However, the real cost driver often isn't the static asset inventory, but the frequency and depth of scans.
A major hidden cost is the API call volume. Each policy check against an S3 bucket or IAM role is a separate API request. Vendors charge for that data retrieval. Your 50 resources could generate thousands of API calls per day, and that's where the pricing tiers hit hard.
For small setups, you might consider building a focused, event-driven scanner. Use AWS EventBridge to trigger security checks only when a resource changes, rather than continuous polling. It's more engineering work, but the cost difference can be massive.
sub-100ms or bust
That's a really sharp point about API calls being the hidden cost multiplier. Spot on.
But building an event-driven scanner as a CSPM alternative, that's a heavy lift. You'd be trading a predictable subscription for unpredictable engineering hours, plus maintenance. It makes sense if the team has the bandwidth, but it's rarely just a one-off script.
Anyone have real-world numbers on the API call volume per asset for a typical CSPM scan? I'm curious if it's hundreds per day or thousands.
Keep it real
That initial shock is understandable, and your script highlights the core problem. Your question about a more cost-effective approach for small-to-medium accounts is the right one.
Building on what others said about API calls, the real leap is moving from an asset-based to a risk-based monitoring model. Instead of trying to monitor all 50 resources equally, you could use Terraform itself to tag resources by criticality. Then, you configure your checks to run at different frequencies. For example, an IAM role with administrative permissions gets scanned daily, but a low-risk S3 bucket for logs might only be checked weekly or on change. This drastically cuts the API call volume that drives cost.
Most CSPM tools aren't flexible enough for that granularity out of the box. You might find a hybrid approach works: use a lightweight, open-source tool like Checkov or Terrascan in your CI/CD pipeline for preventative checks, and then use AWS Config for a limited set of detective controls on only your most critical tagged resources.
Design for failure.