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A Layer 7 DDoS attack uses the seventh protocol of the OSI Model to target the application interface, in the process mimicking real, human behavior that is harder to detect and mitigate.
https://blog.sucuri.net/2014/02/layer-7-ddos-blocking-http-flood-attacks.html
Attack sample.
References
Amazon White Paper- https://d0.awsstatic.com/whitepapers/DDoS_White_Paper_June2015.pdf