Automating application layer DDoS mitigation with Shield Advanced - AWS WAF, AWS Firewall Manager, and AWS Shield Advanced
Caveats

Automating application layer DDoS mitigation with Shield Advanced

This page introduces the topic of automatic application layer DDoS mitigation and lists associated caveats.

You can configure Shield Advanced to respond automatically to mitigate application layer (layer 7) attacks against your protected application layer resources, by counting or blocking web requests that are part of the attack. This option is an addition to the application layer protection that you add through Shield Advanced with an AWS WAF web ACL and your own rate-based rule.

When automatic mitigation is enabled for a resource, Shield Advanced maintains a rule group in the resource's associated web ACL where it manages mitigation rules on behalf of the resource. The rule group contains a rate-based rule that tracks the volume of requests from IP addresses that are known to be sources of DDoS attacks.

Additionally, Shield Advanced compares current traffic patterns against historic traffic baselines to detect deviations that might indicate a DDoS attack. Shield Advanced responds to detected DDoS attacks by creating, evaluating, and deploying additional, custom AWS WAF rules in the rule group.

Caveats for using automatic application layer DDoS mitigation

The following list describes the caveats of Shield Advanced automatic application layer DDoS mitigation, and describes steps that you might want to take in response.

  • Automatic application layer DDoS mitigation works only with web ACLs that were created using the latest version of AWS WAF (v2).

  • Shield Advanced requires time to establish a baseline of your application's normal, historic traffic, which it leverages to detect and isolate attack traffic from normal traffic, to mitigate attack traffic. The time to establish a baseline is between 24 hours and 30 days from the time you associate a web ACL with the protected application resource. For additional information about traffic baselines, see List of factors that affect application layer event detection and mititgation with Shield Advanced.

  • Enabling automatic application layer DDoS mitigation adds a rule group to your web ACL that uses 150 web ACL capacity units (WCUs). These WCUs count against the WCU usage in your web ACL. For more information, see Protecting the application layer with the Shield Advanced rule group, and Web ACL capacity units (WCUs) in AWS WAF.

  • The Shield Advanced rule group generates AWS WAF metrics, but they are not available to view. This is the same as for any other rule groups that you use in your web ACL but do not own, such as AWS Managed Rules rule groups. For more information about AWS WAF metrics, see AWS WAF metrics and dimensions. For information about this Shield Advanced protection option, see Automating application layer DDoS mitigation with Shield Advanced .

  • For web ACLs that protect multiple resources, automatic mitigation only deploys custom mitigations that don't negatively impact any of the protected resources.

  • The time between the start of a DDoS attack and when Shield Advanced places custom automatic mitigation rules varies with each event. Some DDoS attacks might end before the custom rules are deployed. Other attacks might happen when a mitigation is already in place, and so might be mitigated by those rules from the start of the event. Additionally, rate-based rules in the web ACL and Shield Advanced rule group might mitigate attack traffic before it's detected as a possible event.

  • For Application Load Balancers that receive any traffic through a content delivery network (CDN), such as Amazon CloudFront, the application-layer automatic mitigation capabilities of Shield Advanced for those Application Load Balancer resources will be reduced. Shield Advanced uses client traffic attributes to identify and isolate attack traffic from normal traffic to your application, and CDNs may not preserve or forward the original client traffic attributes. If you use CloudFront, we recommend enabling automatic mitigation on the CloudFront distribution.

  • Automatic application layer DDoS mitigation does not interact with protection groups. You can enable automatic mitigation for resources that are in protection groups, but Shield Advanced does not automatically apply attack mitigations based on protection group findings. Shield Advanced applies automatic attack mitigations for individual resources.

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