How to Protect Against DDoS Attacks: The Ultimate Guide for Developers and IT Pros
DDoS attacks continue to be one of the most prevalent and costly threats facing organizations across all industries. Research from Netscout‘s Threat Intelligence Report found that there were 5.4 million DDoS attacks in the first half of 2021 alone, an 11% increase from the same time period in 2020. Attacks are also growing larger and more complex, often combining multiple vectors. Akamai reported mitigating the largest ever DDoS attack at 1.44 Tbps in 2021.
The financial impacts of DDoS are staggering. According to Corero, the average cost of a DDoS attack is $221,836, with larger organizations facing losses of over $2 million per attack. These costs come from lost revenue, reduced productivity, IT overtime, and customer churn. There are also harder to quantify costs like reputational damage and loss of customer trust.
As a full-stack developer and IT professional, it‘s critical that you understand how to protect your organization‘s applications and infrastructure from the ever-growing threat of DDoS attacks. In this ultimate guide, we‘ll dive deep into actionable strategies and best practices you can implement across the development lifecycle to mitigate DDoS risks.
Quick Primer: How DDoS Attacks Work
Before getting into mitigation techniques, let‘s quickly review how DDoS attacks work. A distributed denial-of-service (DDoS) attack seeks to make an online service unavailable by overwhelming it with traffic from multiple sources. The attacker does this by gaining control of a network of internet-connected machines and devices (known as a botnet) and directing them to send a flood of requests to the target all at once.
There are three main categories of DDoS attacks:
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Volumetric Attacks – Attempt to consume the bandwidth of the target network or service. Examples include UDP reflection attacks and ICMP floods.
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Protocol Attacks – Exploit weaknesses in network protocols like SYN to consume server resources and infrastructure like firewalls and load balancers.
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Application Layer Attacks – Target vulnerabilities in web applications with techniques like HTTP floods and Slowloris.
Now that we‘ve covered the basics, let‘s get into the proactive steps you can take as a developer to protect against DDoS.
Mitigation Techniques for Developers
1. Implement Proper Input Validation and Sanitization
One of the most fundamental security practices for preventing application layer DDoS is properly validating and sanitizing all user input. This means checking things like input length, data type, format, and range, and stripping out any potentially malicious characters or scripts.
Input validation should happen on both the client-side and server-side. While client-side validation improves the user experience, it can easily be bypassed. Server-side validation is a must.
Some key best practices:
- Define a whitelist of allowed characters and inputs
- Set maximum length limits on form fields
- Escape special characters like < > & ;
- Validate data formats for fields like email addresses and dates
- Use parameterized queries for databases to prevent SQL injection
2. Use Rate Limiting and Throttling
Rate limiting involves restricting the number of requests a user can send in a given time period. It‘s a simple but effective way to mitigate volumetric and application layer DDoS attacks that attempt to overwhelm your application with a flood of traffic.
Key areas to implement rate limiting include:
- Login forms and authentication flows
- API endpoints
- Resource-heavy pages and searches
- Form submissions
Most web frameworks have built-in or add-on modules for rate limiting. For example, Express.js has middleware like express-rate-limit. If you‘re using a cloud provider, check if they have a native rate limiting service, like AWS WAF.
For API-heavy applications, consider using an API gateway that supports rate limiting policies out of the box. Solutions like Kong and Apigee make it easy to enforce rate limits across your API portfolio.
3. Leverage Asynchronous Processing
Synchronous processing, where each request is handled one at a time and subsequent requests have to wait, is an easy target for DDoS attacks. Attackers can exploit this by sending a flood of slow or computationally heavy requests that tie up your server resources.
Where possible, use asynchronous processing and non-blocking I/O to decouple request processing from responding to the client. This way your application can continue to handle other requests even if some are taking longer to complete.
In Node.js, you can use native modules like cluster and worker_threads to distribute load across multiple processes or threads. Libraries like async make it easy to manage asynchronous control flow.
For queue-based applications, use a robust message broker like RabbitMQ or Apache Kafka. These allow you to decouple producers from consumers and smoothly handle spikes in traffic.
4. Keep Dependencies Up-to-Date
The open source libraries and frameworks that power our applications are unfortunately common sources of DDoS vulnerabilities. Attackers are constantly seeking out and exploiting known flaws in popular dependencies.
A famous example is the Slowloris DDoS attack, which exploited a vulnerability in the Apache web server by sending partial HTTP requests that tied up server threads.
As a developer, you have a responsibility to keep your application‘s dependencies updated and patched. This means:
- Regularly auditing your dependency tree for outdated or vulnerable libraries
- Configuring dependabot or other automated pull request tools to get alerted to new versions
- Prioritizing updates for dependencies with known security issues
- Testing updates thoroughly in staging before deploying to production
Lastly, try to minimize your dependency footprint as much as possible. Don‘t use a library for something you can easily build yourself. More dependencies means a larger attack surface.
5. Load Test Your Application
Load testing involves putting demand on your application and measuring how it responds. It‘s a proactive way to gauge your application‘s performance under stress and identify potential DDoS chokepoints before attackers do.
Some common open source tools for load testing include:
When load testing, gradually increase traffic levels until you start to see degraded performance. Use profiling tools to identify bottlenecks like network calls, database queries, and CPU-intensive operations. Optimize these with techniques like caching, query tuning, and concurrent processing.
Also experiment with different load patterns like sudden spikes vs. steady increases. See how autoscaling rules react. By simulating realistic DDoS scenarios, you‘ll be better prepared to handle the real thing.
Infrastructure Best Practices
Developers aren‘t the only ones who play a role in DDoS mitigation. IT and security teams need to implement safeguards at the infrastructure level as well.
Use Cloud-Based DDoS Mitigation Services
One of the most effective defenses against volumetric DDoS attacks is using a reputable cloud-based mitigation service. These services filter traffic through their globally distributed networks of scrubbing centers, which can absorb even multi-terabit attacks.
Leading providers include:
| Provider | Max Mitigation Capacity | Always-On / On-Demand | Layer 3-7 Protection |
|---|---|---|---|
| Cloudflare Magic Transit | 15+ Tbps | Both | Yes |
| Akamai Prolexic | 8+ Tbps | Both | Yes |
| AWS Shield | Undisclosed | Always-On | Yes |
| Imperva DDoS Protection | 3.5+ Tbps | Both | Yes |
When evaluating providers, consider factors like mitigation capacity, time to mitigate (TTM), service level agreements (SLA), and ease of integration with your existing infrastructure.
Implement a Web Application Firewall
A web application firewall (WAF) is a type of firewall designed to protect HTTP applications from common web-based attacks like SQL injection, cross-site scripting, and of course – HTTP flood DDoS.
WAFs work by inspecting incoming HTTP traffic and applying a combination of signature, anomaly, and reputation-based detection techniques to filter out malicious requests. They commonly come in three deployment models:
- Network-based – Hardware appliances deployed locally in a datacenter
- Host-based – Software agent installed on the web server itself
- Cloud-based – Firewall-as-a-service that proxies your traffic
Cloud-based and host-based WAFs tend to be easier to deploy and manage than network appliances. Many CDN and cloud providers bundle a cloud WAF with their DDoS mitigation service.
Some leading WAF solutions to consider:
- Cloudflare WAF
- Imperva Cloud WAF
- F5 Advanced WAF
- ModSecurity – Open source software WAF
For most organizations, a cloud-based WAF + DDoS mitigation service will provide sufficient protection against application layer DDoS attacks. Those with strict compliance requirements or ultra-low latency apps may need to deploy a local network appliance as well.
Use Anycast for Critical DNS Infrastructure
DNS is a frequent target of DDoS attacks since it‘s a critical dependency for most web applications. Without reliable DNS, clients won‘t be able to resolve your application‘s domain and access it.
One way to increase the resilience of your DNS is by using Anycast routing. Anycast allows multiple geographically distributed servers to advertise the same IP address. When a client makes a DNS query, the request gets routed to the topologically closest server.
The benefits of Anycast for DDoS mitigation are twofold:
- Incoming DDoS traffic is distributed across multiple servers, diluting its impact.
- Legitimate DNS queries can still be served by the closest available server if one goes down.
Most managed DNS providers like Cloudflare, NS1, and Amazon Route53 use Anycast under the hood for enhanced reliability. Alternatively, you can deploy your own Anycast DNS network using software like PowerDNS and gdnsd.
Incident Response Best Practices
Even with all the right defenses in place, some DDoS attacks will inevitably get through. That‘s why having a battle-tested incident response (IR) plan is so crucial.
Key components of a DDoS IR plan:
- Clear roles and responsibilities for all stakeholders
- Contact information for incident commanders, network/IT teams, and external providers
- Communication protocols and status page procedures
- Criteria for activating on-demand cloud mitigation
- Playbooks for different attack scenarios
- Procedures for capturing attack forensics
- Steps for conducting a post-mortem
The specifics of your IR plan will depend on factors like the size of your organization, in-house expertise, and severity of attacks faced. The most important thing is to have one and practice it regularly! Conduct game day exercises at least quarterly where you simulate realistic DDoS scenarios and see how your team responds.
Conclusion: Staying One Step Ahead
DDoS attacks will only continue to grow in frequency and sophistication. Attackers are constantly developing new exploits and attack vectors, so our defenses must evolve as well.
As a developer or IT professional, you play a critical role in protecting your organization from the damaging impacts of DDoS. By implementing secure coding practices, load testing your applications, leveraging cloud-based mitigation services, and having a robust incident response plan, you‘ll be well-positioned to withstand even the largest attacks.
But the work is never done. Make DDoS mitigation a continuous part of your development lifecycle and IT operations. Stay on top of the latest attack trends and tools. By being proactive and adaptive, you can stay one step ahead of the bad actors and keep your applications safe and reliable for your end-users.