Services or capabilities described in Amazon Web Services documentation might vary by Region. To see the differences applicable to the China Regions, see Getting Started with Amazon Web Services in China (PDF).

Application layer event details

You can see details about an application layer event's detection, mitigation, and top contributors in the bottom section of the console page for the event. This section can include a mix of legitimate and potentially unwanted traffic, and may represent both traffic that was passed to your protected resource and traffic that was blocked by Shield Advanced mitigations.

The mitigation details are for any rules in the web ACL that's associated with the resource, including rules that are deployed specifically in response to an attack and rate-based rules that are defined in the web ACL. If you enable automatic application layer DDoS mitigation for an application, the mitigation metrics include metrics for those additional rules. For information about these application layer protections, see Amazon Shield Advanced application layer (layer 7) protections.

Detection and mitigation

For an application layer (layer 7) event, the Detection and mitigation tab shows detection metrics that are based on information obtained from the Amazon WAF logs. Mitigation metrics are based on Amazon WAF rules in the associated web ACL that are configured to block the unwanted traffic.

For Amazon CloudFront distributions, you can configure Shield Advanced to apply automatic mitigations for you. With any application layer resources, you can choose to define your own mitigating rules in your web ACL and you can request help from the Shield Response Team (SRT). For information about these options, see Responding to DDoS events.

The following screenshot shows an example of the detection metrics for an application layer event that subsided after a number of hours.

Event traffic that subsides before a mitigating rule takes effect isn't represented in mitigation metrics. This can result in a difference between the web request traffic shown in the detection graphs and the allow and block metrics shown in the mitigation graphs.

Top contributors

The Top contributors tab for application layer events displays the top 5 contributors that Shield has identified for the event, based on the Amazon WAF logs that it has retrieved. Shield categorizes the top contributors information by dimensions such as source IP, source country, and destination URL.

Use the Shield application layer top contributors information only to get a general idea of the nature of an attack, and do not base your security decisions on it. For application layer events, the Amazon WAF logs are the best source of information for understanding the contributors to an attack and for devising your mitigation strategies.

The Shield top contributors information doesn't always completely reflect the data in the Amazon WAF logs. When it ingests the logs, Shield prioritizes reducing the impact to system performance over retrieving the complete set of data from the logs. This can result in a loss of granularity in the data that's available to Shield for analysis. In most cases, the majority of the information is available, but it's possible for the top contributor data to be skewed to some degree for any attack.

The following screenshot shows an example Top contributors tab for an application layer event.

Contributor information is based on requests for both legitimate and potentially unwanted traffic. Larger volume events and events where the request sources aren't highly distributed are more likely to have identifiable top contributors. A significantly distributed attack could have any number of sources, making it hard to identify top contributors to the attack. If Shield Advanced doesn't identify significant contributors for a specific category, it displays the data as unavailable.