Which AWS security service protects applications from distributed denial of service attacks with always-on detection and automatic inline mitigations?

Explanations:

Amazon Inspector is primarily used for assessing the security and compliance of applications running on AWS. It does not specifically protect against DDoS attacks.

AWS Web Application Firewall (AWS WAF) helps protect web applications from common web exploits, but it does not provide DDoS protection with automatic inline mitigations.

Elastic Load Balancing (ELB) distributes incoming application traffic across multiple targets, but it does not offer dedicated DDoS protection features.

AWS Shield is a managed DDoS protection service that provides always-on detection and automatic inline mitigations against DDoS attacks, making it the correct answer.