Distributed Denial of Service (DDoS) attacks are a significant threat to cloud infrastructure. They aim to make your services unavailable by overwhelming them with traffic from multiple sources. Below are detailed methods to harden your cloud infrastructure against such attacks.

1. Understanding DDoS Attacks

Before implementing protective measures, it’s important to understand the types of DDoS attacks:

• Volume-Based Attacks: These include UDP floods, ICMP floods, and other spoofed-packet floods. The attack’s goal is to saturate the bandwidth of the targeted site.
• Protocol Attacks: These attacks, such as SYN floods, Ping of Death, and Smurf DDoS, exploit weaknesses in the layer 3 and layer 4 protocol stack.
• Application Layer Attacks: These are sophisticated attacks targeting applications directly, often with fewer resources but targeting the most critical aspects of your service.

2. Designing a Resilient Infrastructure

A proactive approach in design can minimize DDoS attack impact:

• Distribute Resources: By using a multi-zone or multi-region deployment, you can distribute resources and reduce the risk of system failure due to localized attacks.
• Scalability: Implement auto-scaling policies to handle unexpected traffic loads.
• Redundancy: Ensure key components are duplicated across different locations to mitigate the risk of a single point of failure.

3. Implementing Network Security Measures

Employing numerous network-level defenses is crucial:

• Firewalls: Set up web application and network firewalls to filter out malicious traffic.
• Anti-DDoS Hardware and Software: Utilize DDoS mitigation hardware or cloud-based software solutions that can absorb and scrub traffic.
• Traffic Shaping: Use rate limiting to control the traffic allowed to reach your infrastructure.

4. Monitor and Analyze

Constant vigilance is key to early detection:

• Monitoring Tools: Utilize tools that provide real-time analytics about traffic and automatically alert on unusual patterns.
• Log Analysis: Regularly review system logs to identify potential security threats.
• Anomaly Detection: Implement automated systems that use machine learning to detect abnormal behavior indicative of a DDoS attack.

5. Using Cloud Services’ DDoS Protection

Many cloud providers offer built-in DDoS protection:

• AWS Shield: This service provides always-on detection and inline mitigation capabilities designed to protect your AWS resources.
• Azure DDoS Protection: Offers enhanced DDoS mitigation features for Azure resources.
• Google Cloud Armor: Provides a range of security features, including DDoS defense.

6. Content Delivery Network (CDN)

CDNs can distribute and balance the traffic across a global network:

• Edge Servers: CDNs use edge servers located closer to the user to absorb and mitigate attacks.
• Caching: By caching content at the edge, CDNs reduce the number of requests that reach your core infrastructure.

7. Best Practices for Operations

Adherence to operational best practices is fundamental:

• Staff Training: Ensure staff are trained on DDoS risk mitigation and response procedures.
• Incident Response Plan: Have a DDoS incident response plan that includes roles, responsibilities, and communication strategies.
• Regular Audits: Conduct security audits and penetration testing to find and fix vulnerabilities.

8. Collaboration and Support

Finally, nobody is an island in the face of DDoS:

• Peering Relationships: Communicate with your ISP or hosting provider to ensure they have DDoS mitigation policies and can support you during an attack.
• Community Support: Join security forums to stay updated on the latest DDoS trends and threat intelligence.

In conclusion, hardening your cloud infrastructure against DDoS attacks requires a multifaceted approach that includes solid design principles, implementing robust security technologies, continuous monitoring and analysis, utilization of cloud and CDN services, adherence to operational best practices, and active collaboration. Given the evolving nature of DDoS attacks, it is important to remain vigilant and regularly update your defense mechanisms to protect your cloud assets effectively.