I’ve been trying to model the monthly cost for a new WAFv2 deployment with a few custom rules and managed rule groups. The official AWS pricing page breaks it down into “Web ACLs,” “Rules,” and “Requests,” which seems straightforward. But when I plug numbers into the AWS Pricing Calculator, the output feels… disconnected from reality.
For example, the calculator asks for "Number of Web ACLs" and "Number of Rules." However, a single Web ACL can have many rules, and managed rule groups count as *one* rule but are priced per rule group *and* per million requests. The calculator doesn't have a field to specify which rules are managed versus custom, making the estimate wildly inaccurate. If I add a rule group like `AWSManagedRulesCommonRuleSet`, do I also need to manually account for its per-request cost separately? The documentation implies yes, but the calculator doesn't guide you there.
Has anyone else encountered this? Specifically:
* How do you accurately forecast costs when using a mix of managed rule groups (which have a monthly charge *and* a per-request charge) and custom rules (which just have the per-rule charge)?
* Is there a methodology or a third-party tool you use to get a predictable monthly figure, especially when request volumes can spike?
I’m concerned about budget variance, particularly since WAF costs can scale with both infrastructure *and* threat landscape changes. A detailed breakdown of your own costing approach would be invaluable.
—A
Every dollar counts.
You're definitely not the only one. The calculator is borderline useless for WAFv2 because it ignores the pricing model's fundamental complexity.
The only reliable method I've found is to abandon the calculator entirely. Build your own spreadsheet. Model it like this:
* A fixed monthly cost for each Web ACL.
* A fixed monthly cost for each *custom* rule (the calculator's "Rules" field).
* For each managed rule group, add its fixed monthly fee PLUS an estimated per-request cost.
That last bit is what the calculator completely misses, making its output pure fantasy.
Third-party tools? They're just guessing unless they're parsing your actual configuration. You're better off with a simple spreadsheet you can control, then run a cost allocation report in Cost Explorer after the first month to see how wrong you were.
trust but verify
Yeah, the calculator's oversimplification with "Number of Rules" is the core issue. It treats all rules the same, but a managed rule group is a single rule entry with a dual cost structure.
I've started using a hybrid approach. I use the calculator *only* for the raw Web ACL and custom rule baseline. Then I layer in the managed rule group costs manually in a separate sheet.
For your `AWSManagedRulesCommonRuleSet` question: yes, you absolutely need to account for its per-request cost separately. The calculator's "Requests" field is a global bucket, so it won't distinguish between requests processed by a custom rule versus a managed rule group. Your model needs to estimate the portion of total requests hitting each managed group and calculate that fee independently.