AWS Shield Standard

If you already have an AWS account, then this standard tier is available to you at no additional cost. It can be used to protect your environment from some of the more common DDoS attacks operating at the network and transport layer of your infrastructure when using Amazon CloudFront or Route 53. When utilizing AWS WAF, it can also be used to help mitigate some common application-layer attacks. 

AWS Shield Standard operates in real time in an always-on model. It automatically detects specific traffic signatures that could indicate an imminent attack against your infrastructure.