1. Deployment and Scalability: AWS Shield is a cloud-based security service provided by Amazon Web Services, offering distributed denial of service (DDoS) protection for applications running on AWS. It leverages the scaling capabilities of the cloud to automatically detect and mitigate DDoS attacks in real time. On the other hand, Snort is an open-source intrusion detection and prevention system (IDPS) that requires local deployment on servers or network devices. While it can offer scalability through distributed setups, the process of deploying and managing Snort instances across multiple locations can be more complex compared to AWS Shield.

2. Detection Mechanisms: AWS Shield primarily focuses on DDoS attack detection and mitigation. It utilizes a combination of heuristics, anomaly detection, and traffic analysis to identify and filter out malicious traffic patterns that could potentially overwhelm an application or network. In contrast, Snort is a versatile IDPS that enables the detection of a wider range of threats, including network-based attacks, malware infections, and policy violations. With its extensive rule-based detection capabilities, Snort can be customized to detect specific patterns or behaviors tailored to an organization's security requirements.

3. Management and Maintenance: AWS Shield is a fully managed service, meaning that AWS takes care of the underlying infrastructure and maintenance tasks. Users can rely on AWS's expertise and automated mitigation techniques to handle DDoS attacks. Meanwhile, Snort requires manual management and maintenance by network administrators or security teams. This includes configuring rule sets, monitoring system health, and ensuring regular updates to maintain maximum effectiveness.

4. Cost Structure: AWS Shield is typically offered as part of an existing AWS subscription and provides various protection tiers to suit different customer needs. The cost is based on the level of protection and additional features required. Snort, being an open-source tool, is free to use. However, organizations are responsible for the associated infrastructure costs, such as hardware, storage, and network resources required to support Snort's deployment and operation.

5. Flexibility and Customization: Snort offers a high level of customization, allowing users to define their own detection rules and filters to adapt to specific network environments and security policies. This flexibility enables fine-tuning and tailoring the IDPS to the unique requirements of an organization. In contrast, AWS Shield provides a more standardized approach to DDoS protection, with predefined mitigation techniques that do not offer the same level of customization as Snort.

6. Integration and Ecosystem: Snort is a popular open-source tool that has a large and active community of users and developers. This community-driven ecosystem ensures regular updates, bug fixes, and the availability of a wide range of add-ons and plugins. AWS Shield, while benefiting from the robust AWS infrastructure, has a more closed ecosystem and is tightly integrated with other AWS services, making it a suitable choice for organizations heavily invested in the AWS ecosystem.

In Summary, while AWS Shield is a cloud-based DDoS protection service that offers automated mitigation and scalability, Snort is an open-source IDPS that provides a wide range of customizable security features for on-premises or distributed environments. The choice between the two depends on factors such as deployment requirements, desired level of customization, and integration with existing infrastructure.