How to Protect an Apache Web Server from DDoS Attacks

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Dimitri Nek
Dimitri Nek
Web Hosting Geek

Apache server protection

Ensuring the security and stability of web servers is crucial for businesses and organizations of all sizes. Among the many threats faced by web servers, DDoS attacks stand out as one of the most disruptive and challenging to mitigate.

In this guide, we will focus on Apache Web Server, a popular open-source web server software, explore various techniques and tools to protect it from DDoS attacks, discuss best practices for server configuration, and recommend security tools that can help keep your Apache safe and operational.

Let’s get started!

Key Takeaways:

  • DDoS attacks are malicious attempts to overwhelm a targeted system, such as a web server, with a massive amount of traffic from multiple sources. They can cause significant damage, including downtime, loss of revenue, and a tarnished reputation.
  • To make an Apache Web Server more resilient to DDoS attacks, consider limiting the request rate and size, adjusting timeout settings, and disabling unnecessary modules.
  • Firewalls, access control, web application firewalls, and specific modules like ModSecurity and Mod_evasive can be effective in preventing and mitigating DDoS attacks.
  • Regularly monitoring and analyzing server traffic is crucial for detecting DDoS attacks and mitigating their impact. Keeping a close eye on server logs and using traffic analysis tools can provide valuable insights.
  • Understanding the mechanics of DDoS attacks, optimizing server configuration, employing firewalls and other security tools, and monitoring server traffic are critical for ensuring the availability, performance, and integrity of a web server.

What is a DDoS Attack?

server ddos attacked

A Distributed Denial of Service attack is a malicious attempt to overwhelm a targeted system, such as a web server, with a massive amount of traffic from multiple sources. These attacks aim to exhaust the target server’s resources, making it unavailable to legitimate users.

DDoS attacks can cause significant damage, including downtime, loss of revenue, and a tarnished reputation.

Example 1: Traffic Jam

Imagine you’re driving to your favorite coffee shop during rush hour. Under normal circumstances, traffic is manageable, and you reach your destination without any major delays. However, one day, a group of people decides to coordinate and flood the streets with their vehicles, causing a massive traffic jam. This orchestrated action prevents you and other legitimate drivers from reaching your destinations.

In this scenario, the traffic jam is similar to a DDoS attack on a web server, where malicious actors flood the server with traffic, preventing legitimate users from accessing the website or service.

Example 2: Overwhelming a Phone Line

Picture a small bakery that receives orders through its phone line. During regular business hours, they can manage incoming calls and fulfill orders for their customers. Now imagine that a group of pranksters decides to target the bakery by continuously calling the bakery’s phone line simultaneously from multiple phones. The bakery’s phone line becomes overwhelmed, making it nearly impossible for genuine customers to place their orders.

This situation is analogous to a DDoS attack, where attackers use multiple sources to inundate a web server with requests, making it difficult or impossible for legitimate users to access the website or service.

Types of DDoS Attacks

attacked server

There are multiple categories of DDoS attacks, each focusing on distinct aspects of a web server’s infrastructure. Familiarizing yourself with the different attack categories enables you to better equip your Apache Web Server to resist these threats. Some prevalent DDoS attack categories include:

  1. Volumetric Attacks: These attacks seek to use up a target’s available bandwidth by inundating the network with a massive volume of traffic. Volumetric attacks, such as UDP floods and ICMP (ping) floods, generate substantial traffic by exploiting vulnerable devices like unprotected IoT devices. Consequently, the target’s network capacity becomes overwhelmed, making the server unreachable for legitimate users.
  2. Protocol Attacks: Protocol attacks take advantage of weaknesses in network protocols like TCP, UDP, or ICMP to deplete server resources or disrupt network communication. SYN flood attacks serve as a prime example, where an attacker sends a large number of SYN (synchronize) packets to a target server without completing the TCP handshake. This forces the server to allocate resources for connections that never fully form, ultimately leading to resource exhaustion and server unresponsiveness.
  3. Application-Layer Attacks: Also known as Layer 7 attacks, these target the application layer of the OSI model, where web servers and web applications function. Application-layer attacks often resemble legitimate traffic, making them more challenging to detect and block. HTTP floods, Slowloris, and low-and-slow attacks are examples of this attack category. By exploiting vulnerabilities or weaknesses in web applications, attackers can consume server resources, disrupt service, or obtain unauthorized access.
  4. Amplification Attacks: Amplification attacks leverage the connectionless nature of specific protocols, such as DNS or NTP, to produce an enormous volume of traffic directed at the target. In a typical amplification attack, an attacker sends small requests with a spoofed IP address (the target’s IP) to vulnerable servers. The servers respond with significantly larger responses, which are then directed at the target, overwhelming their network capacity.
  5. Distributed Reflection and Amplification (DrDoS) Attacks: DrDoS attacks merge the techniques used in reflection and amplification attacks, using multiple intermediary servers to direct amplified traffic toward the target. Attackers send requests with a spoofed IP address to vulnerable servers, which then respond with large amounts of traffic aimed at the target. By employing multiple reflection points, attackers can generate substantial traffic, making it challenging to trace the attack source and complicating mitigation efforts.
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Recognizing these various DDoS attack categories helps you apply suitable security measures and monitoring strategies to safeguard your Apache Server from potential threats. Each attack category necessitates a different approach to detection and mitigation, so it is crucial to establish a comprehensive security plan that addresses all possible attack vectors.

Essential Apache Configuration Tweaks

server configured

To improve the security of an Apache Web Server and make it more resilient to DDoS attacks, consider implementing the following configuration changes:

  1. Limit Request Rate: Use the mod_ratelimit module to control the rate at which clients can send requests to the web server.
  2. Limit Request Size: Set the LimitRequestBody directive to limit the size of incoming HTTP requests, preventing large request floods.
  3. Timeout Settings: Adjust the Timeout and KeepAliveTimeout settings to reduce the time a connection can remain idle, freeing up resources for legitimate traffic.
  4. Disable Unnecessary Modules: Deactivate any modules that are not in use to minimize the server’s attack surface.
Configuration Directive Description Recommended Value
mod_ratelimit Controls the rate of incoming requests Enable and configure as needed
LimitRequestBody Limits the size of HTTP requests 1 MB (1048576)
Timeout Sets the maximum time for an idle connection 60 seconds
KeepAliveTimeout Specifies the time for an idle keep-alive connection 5 seconds

Tools and Techniques to Prevent and Mitigate DDoS Attacks

protected server

Implementing Firewalls and Access Control

Firewalls can be an effective first line of defense against DDoS attacks. By filtering incoming traffic based on predefined rules, firewalls can block malicious traffic while allowing legitimate requests to pass through. Consider using a combination of network firewalls, application firewalls, and intrusion prevention systems (IPS) to maximize protection.

  1. Network Firewalls: These firewalls filter traffic based on IP addresses, ports, and protocols. Configure your network firewall to allow traffic only from trusted sources and block known malicious IP addresses.
  2. Application Firewalls: Application firewalls like mod_security for Apache Web Server can inspect incoming traffic at the application layer, providing more fine-grained control and blocking application-specific attacks.
  3. IPS: An IPS monitors network traffic for signs of malicious activity and can automatically block traffic that matches known attack patterns.

Deploying a Web Application Firewall

A Web Application Firewall is specifically designed to protect web applications from various threats, including DDoS attacks. WAFs can analyze incoming HTTP requests and block those that violate predefined security rules.

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Some popular WAFs include:

Web Application Firewall Description
ModSecurity An open-source WAF that integrates with Apache Web Server and provides real-time application protection
Cloudflare A cloud-based WAF that offers DDoS protection, CDN, and other security features
Sucuri A comprehensive website security platform that includes a WAF, DDoS protection, and malware removal

By deploying a WAF, you can enhance your Apache Web Server’s security and mitigate the impact of DDoS attacks.

Enhancing Security with ModSecurity

server secured

ModSecurity, also known as ModSec, is a popular open-source Web Application Firewall that works with Apache, Nginx, and other web servers. It provides robust protection against various security threats, including SQL injection, cross-site scripting (XSS), and DDoS attacks. ModSecurity inspects incoming HTTP requests and responses, allowing it to block, log, or modify requests based on a set of customizable rules.

How ModSecurity Works

ModSecurity operates at the application layer, providing a deeper level of protection than traditional network firewalls. It uses a rule-based approach to analyze HTTP traffic and can be configured to detect and block a wide range of attacks. Key features of ModSecurity include:

  1. Rule-based Detection: ModSecurity uses a comprehensive set of predefined rules to detect and block various types of attacks. You can also create custom rules to address specific threats or vulnerabilities.
  2. Real-time Monitoring: ModSecurity inspects incoming and outgoing HTTP traffic in real-time, allowing it to detect and respond to threats as they occur.
  3. Logging and Reporting: ModSecurity can generate detailed logs and reports about security events, providing valuable insights for further analysis and response.
  4. Virtual Patching: ModSecurity can be used to create virtual patches for known vulnerabilities, providing temporary protection until a permanent fix is available.

Configuring ModSecurity for DDoS Protection

To utilize ModSecurity for DDoS protection on your Apache Web Server, follow these steps:

  1. Install ModSecurity: Depending on your system, you may need to install ModSecurity through your package manager or compile it from source.
  2. Enable ModSecurity: Once installed, enable ModSecurity in your Apache configuration. This typically involves adding a LoadModule directive to your configuration file.
  3. Configure ModSecurity settings: Customize ModSecurity’s behavior by setting various configuration directives and selecting a rule set. The OWASP ModSecurity Core Rule Set (CRS) is a popular choice that provides comprehensive protection against common web application threats, including DDoS attacks.
  4. Fine-tune rules: Adjust the rules to suit your specific needs and reduce the risk of false positives. This may involve modifying existing rules or creating custom rules to address specific threats.

By implementing ModSecurity, you can significantly enhance the security of your Apache Web Server and protect it against DDoS attacks and other application-layer threats. This powerful WAF offers real-time monitoring, rule-based detection, and virtual patching capabilities, providing a robust layer of protection for your website or service.

Utilizing Mod_evasive to Protect Your Apache Web Server

protected server

Mod_evasive is an Apache module designed to provide protection against DDoS attacks, especially those targeting the HTTP layer. It detects and reacts to patterns that resemble DDoS attacks, such as multiple requests from a single IP address within a short period or a high number of simultaneous requests to the same resource. When a potential attack is detected, mod_evasive blocks the offending IP address and can also be configured to notify the server administrator.

How Mod_evasive Works

Mod_evasive employs a number of techniques to identify and block DDoS attacks:

  1. Request Tracking: Mod_evasive maintains an internal hash table to track the request rate and source of incoming requests. This allows it to identify potential attackers based on their request patterns.
  2. IP Blocking: If mod_evasive determines that an IP address is participating in a DDoS attack, it will block the IP, preventing further requests from that address.
  3. Notifications: Mod_evasive can be configured to send notifications, such as emails or system logs, to the server administrator when an attack is detected. This allows for faster response and mitigation of potential threats.

Configuring Mod_evasive

To use mod_evasive with your Apache Web Server, follow these steps:

  1. Install mod_evasive: Depending on your system, you may need to install mod_evasive through your package manager or compile it from source.
  2. Enable mod_evasive: Once installed, enable mod_evasive in your Apache configuration. This typically involves adding a LoadModule directive to your configuration file.
  3. Configure mod_evasive settings: You can customize mod_evasive’s behavior by setting various configuration directives, such as DOSHashTableSize, DOSPageCount, DOSSiteCount, and DOSBlockingPeriod. These directives allow you to fine-tune mod_evasive’s detection and blocking mechanisms according to your server’s requirements and traffic patterns.
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By implementing mod_evasive, you can add an additional layer of protection against DDoS attacks on your Apache Web Server. This module can help you identify and block malicious traffic, ensuring the availability and performance of your website or service for legitimate users.

Monitoring and Analyzing Server Traffic

monitored server

In addition to the proactive measures mentioned in previous sections, regularly monitoring and analyzing server traffic is crucial for detecting DDoS attacks and mitigating their impact.

By keeping a close eye on traffic patterns and server performance, you can identify unusual activity or spikes in traffic that may indicate an ongoing attack. Tools like log analyzers, network monitoring software, and intrusion detection systems can provide valuable insights and help you stay on top of potential threats. By adopting a comprehensive monitoring strategy, you can respond to DDoS attacks more effectively and ensure the continued availability of your Apache Web Server for legitimate users.

Keep a Close Eye on Server Logs

Regularly monitoring server logs can help you detect unusual activity and identify potential threats. Apache Web Server generates several log files, including access logs and error logs, which can provide valuable information about incoming traffic and server performance. Use log analysis tools to filter, aggregate, and visualize log data, making it easier to spot trends and anomalies.

Use Traffic Analysis Tools

Traffic analysis tools can help you gain insights into your server’s traffic patterns, making it easier to identify and respond to potential DDoS attacks. Tools like NetFlow, sFlow, and Wireshark can provide real-time traffic analysis and help you uncover the source and nature of attacks.


Protecting an Apache Web Server from DDoS attacks is an essential aspect of maintaining a secure and stable online presence.

By understanding the mechanics of DDoS attacks, optimizing server configuration, employing firewalls and other security tools, and monitoring server traffic, you can effectively defend your server against these disruptive threats.

A proactive and informed approach to security is critical for ensuring the availability, performance, and integrity of your web server.


  1. How can I detect a DDoS attack on my Apache Web Server?

    Detecting a DDoS attack on your Apache Server involves monitoring server logs, resource usage, and traffic patterns. Unusually high traffic volumes, server resource exhaustion, or a sudden increase in error logs may indicate an ongoing DDoS attack. Using traffic analysis tools and setting up alerts can help you identify potential attacks more quickly.

  2. Can I completely prevent DDoS attacks on my Apache Web Server?

    While it’s impossible to entirely prevent DDoS attacks, you can significantly reduce their impact by implementing a robust security strategy. This includes optimizing server configuration, deploying firewalls and intrusion prevention systems, using a Web Application Firewall, and regularly monitoring server traffic. Taking a proactive approach to security can help you minimize the risk and consequences of DDoS attacks.

  3. What is the difference between a DoS and a DDoS attack?

    A Denial of Service (DoS) attack aims to disrupt a targeted system by overwhelming it with a flood of traffic from a single source. In contrast, a Distributed Denial of Service (DDoS) attack originates from multiple sources, making it more difficult to block and trace. DDoS attacks are generally more powerful and challenging to mitigate than DoS attacks.

  4. Can Content Delivery Networks help protect my Apache Web Server from DDoS attacks?

    Yes, Content Delivery Networks can help protect your Apache Server from DDoS attacks. CDNs distribute your web content across multiple servers in different geographic locations, which can help absorb and distribute the traffic generated by DDoS attacks. Additionally, many CDNs offer built-in security features, such as DDoS protection and Web Application Firewalls (WAF), further enhancing your server’s security.

  5. What is the role of a Web Application Firewall (WAF) in protecting my Apache Web Server from DDoS attacks?

    A Web Application Firewall is specifically designed to protect web applications, including Apache, from various threats, including DDoS attacks. WAFs analyze incoming HTTP requests and block those that violate predefined security rules. By deploying a WAF, you can enhance your server’s security, making it more resilient to DDoS attacks and other threats targeting the application layer.


1 Comment

  • Avatar IT support Uk says:

    To run a really tight ship, you’ll want to stop users from setting up .htaccess files which can override security features you’ve configured

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