/waf

Creating a Web ACL and Associating It with a Resource

Overview

Domain expertise for putting AWS WAF in front of an application: creating a web access control list (web ACL) and associating it with the resource it protects. Covers the immutable scope choice (CLOUDFRONT in us-east-1 versus REGIONAL in the resource's Region), the fact that a web ACL filters nothing until it is associated, the one-web-ACL-per-resource and CloudFront-only constraints, and starting rules in Count mode.

Does not cover the rules that go inside the web ACL (managed rules, rate-based, match, bot, fraud); those are separate references. CloudFront distribution and Application Load Balancer configuration are their own skills.

Execute commands using the AWS MCP server when connected (sandboxed execution, audit logging, observability). Fall back to the AWS CLI otherwise.

Table of Contents

• Overview
• Workflow
• Decision: scope
• Least-privilege IAM
• A web ACL filters nothing until associated
• One web ACL per resource, CloudFront is exclusive
• Start rules in Count mode
• Troubleshooting
• Procedure
• Security Considerations
• Additional Resources

Workflow

To create a web ACL and associate it end to end, follow the procedure exactly. See the Procedure section below.

The procedure covers:

• Choosing the scope from the resource type
• Creating the web ACL with a default action
• Associating it with the resource
• Confirming the association and surfacing the console link

Decision: scope

Constraints:

• You MUST set the scope from the resource type before creating the web ACL; scope is immutable after creation
• You MUST create a CLOUDFRONT web ACL in us-east-1 regardless of where the distribution serves
• You MUST create a REGIONAL web ACL in the same Region as the resource it protects

Least-privilege IAM

The credentials that run these commands should carry only the WAF actions the task needs, not broad access.

Constraints:

• You MUST grant only the specific wafv2: actions these procedures use — for the entry-point workflow that is wafv2:CreateWebACL, wafv2:GetWebACL, wafv2:UpdateWebACL, and wafv2:AssociateWebACL — rather than wafv2:* or the AWSWAFFullAccess managed policy
• You SHOULD extend the same least-privilege approach to the other references (for example wafv2:PutLoggingConfiguration for logging, wafv2:CreateIPSet/wafv2:UpdateIPSet for IP sets), granting only what each task requires
• You MUST use IAM roles with temporary credentials (such as an EC2 instance profile, SSO session, or aws sts assume-role) rather than long-lived IAM user access keys when running these commands

A web ACL filters nothing until associated

A web ACL inspects no traffic until it is associated with a resource. Customers finish the web ACL and assume traffic is filtered.

Constraints:

• You MUST treat the association as a required closing step, not optional
• You MUST confirm the resource is associated before reporting the setup complete

One web ACL per resource, CloudFront is exclusive

Each resource can have only one web ACL, and a web ACL associated with a CloudFront distribution cannot be associated with any other resource type. Customers design around a shared web ACL that cannot exist.

Constraints:

• You MUST NOT associate more than one web ACL with a single resource
• You MUST NOT reuse a CloudFront-associated web ACL on a regional resource
• You SHOULD explain these constraints before the customer designs a shared web ACL

Start rules in Count mode

Enabling rules straight to Block can take down legitimate traffic. The recommended path for a first web ACL is Count, then Block after review.

Constraints:

• You SHOULD start new rules in Count mode and move them to Block only after the customer reviews the matches
• You SHOULD confirm logging is set up first so Count-mode matches are reviewable

Troubleshooting

A CloudFront distribution does not appear in the association list

The web ACL was created in the wrong scope or Region. Recreate it as CLOUDFRONT scope in us-east-1 (Decision: scope).

Rules are configured but traffic is not filtered

The web ACL is not associated with the resource. Associate it (A web ACL filters nothing until associated).

A web ACL cannot be reused across CloudFront and a regional resource

CloudFront web ACLs are exclusive and each resource takes one web ACL. Create separate web ACLs (One web ACL per resource, CloudFront is exclusive).

Procedure

Overview

This procedure creates a web ACL in the correct scope, associates it with the resource, and surfaces the console link to verify.

Parameters

• web_acl_name (required): A name for the web ACL.
• resource_arn (required): The ARN of the resource to protect.
• scope (required): CLOUDFRONT or REGIONAL, derived from the resource type.
• default_action (required): Allow or Block when no rule matches. Set this deliberately to match the intended posture; an Allow default passes any traffic not matched by a rule through unfiltered, so prefer Block as the secure default and use Allow only when explicit blocking rules carry the enforcement.

Constraints for parameter acquisition:

• You MUST ask for all required parameters upfront in a single prompt
• You MUST derive the scope and Region from the resource type, not from the customer's working Region

Steps

1. Verify dependencies

Constraints:

• You MUST confirm credentials with aws sts get-caller-identity
• You MUST confirm the resource exists in the expected Region

2. Create the web ACL

Constraints:

• You MUST create the web ACL in the correct scope and Region:

  aws wafv2 create-web-acl --name {web_acl_name} --scope {scope} \
    --default-action {default_action}={} \
    --visibility-config SampledRequestsEnabled=true,CloudWatchMetricsEnabled=true,MetricName={web_acl_name} \
    --region {region}

• You MUST capture the web ACL ARN and id from the response

3. Associate the web ACL with the resource

Constraints:

• You MUST associate the web ACL with the resource ARN:

  aws wafv2 associate-web-acl --web-acl-arn {web_acl_arn} --resource-arn {resource_arn} --region {region}

• You MUST NOT consider the setup complete until the association succeeds

4. Confirm and surface the console link

Constraints:

• You MUST confirm the association and present the AWS WAF console link, telling the customer to open it and confirm the web ACL and its associated resource:

  https://us-east-1.console.aws.amazon.com/wafv2/homev2/web-acls?region={region}

Example

Example input

{
  "web_acl_name": "example-frontend-webacl",
  "resource_arn": "arn:aws:cloudfront::111122223333:distribution/EDFDVBD6EXAMPLE",
  "scope": "CLOUDFRONT",
  "default_action": "Block"
}

(Block is the secure default — unmatched requests are denied, and Allow rules admit the traffic you intend. Use "default_action": "Allow" only when the customer explicitly wants an allow-by-default web ACL whose rules do the blocking.)

Example output

Created CLOUDFRONT web ACL example-frontend-webacl in us-east-1 with default action Block.
Associated it with distribution EDFDVBD6EXAMPLE.
Open the AWS WAF console and confirm the web ACL and its associated resource:
https://us-east-1.console.aws.amazon.com/wafv2/homev2/web-acls?region=us-east-1

Troubleshooting

The distribution is missing from the association list

The web ACL is in the wrong scope or Region. Recreate as CLOUDFRONT in us-east-1 (Step 2).

Traffic is not being filtered

The web ACL is not associated. Associate it (Step 3).

Security Considerations

This procedure modifies a security control, so misconfiguration directly weakens the application's defenses.

• Least-privilege IAM. You MUST grant only the specific wafv2: actions a task needs (for example wafv2:GetWebACL and wafv2:UpdateWebACL) rather than wafv2:* or the AWSWAFFullAccess managed policy.
• Ephemeral credentials. You MUST use IAM roles with temporary credentials (such as an EC2 instance profile, SSO session, or aws sts assume-role) rather than long-lived IAM user access keys when running these WAF CLI commands.
• Monitor configuration changes. You SHOULD enable AWS CloudTrail on wafv2 management events and set CloudWatch alarms on critical web ACL configuration changes (such as DeleteWebACL and UpdateWebACL rule removals) and on the web ACL's BlockedRequests and CountedRequests metrics, so rule changes and sudden spikes in blocked or counted traffic are detected.

Additional Resources

• Resources that you can protect with AWS WAF (AWS WAF Developer Guide)
• Creating a web ACL in AWS WAF (AWS WAF Developer Guide)
• Associating or disassociating protection with an AWS resource (AWS WAF Developer Guide)