# Distributed Denial Of Service Attacks

## DOS

* A denial-of-service (DoS) attack is a deliberate attempt to make a website or application unavailable to users.
  * An attacker might flood a website or application with excessive network traffic until the targeted website or application becomes overloaded and is no longer able to respond. If the website or application becomes unavailable, this **denies service to users who are trying to make legitimate requests**.

### Some Types of DOS

1. UDP Flood
2. HTTP Level attack
3. Slow loris attack

## DDOS

* In a distributed denial-of-service (DDoS) attack, multiple sources are used to start an attack that aims to make a website or application unavailable.
* This can come from a group of attackers, or even a single attacker. The single attacker can use multiple infected computers (also known as “bots”) to send excessive traffic to a website or application.

## AWS Solution to DDOS

### AWS Shield

* AWS Shield is a service that protects applications against DDoS attacks. AWS Shield provides two levels of protection: Standard and Advanced.
* Standard
  * **AWS Shield Standard** automatically protects all AWS customers at **no cost**. It protects your AWS resources from the most common, frequently occurring types of DDoS attacks.
  * As network traffic comes into your applications, AWS Shield Standard uses a variety of analysis techniques to detect malicious traffic in real time and automatically mitigates it.
* Advanced
  * **AWS Shield Advanced** is a **paid service** that provides detailed attack diagnostics and the ability to detect and mitigate sophisticated DDoS attacks.
  * It also integrates with other services such as `Amazon CloudFront`, `Amazon Route 53`, and `Elastic Load Balancing`. Additionally, you can integrate AWS Shield with AWS WAF _(Web Application Firewall)_ by writing custom rules to mitigate complex DDoS attacks.

### Solutions to some types of DOS

* Security groups to prevent UDP Flood and reflection attacks by configuring right policies.
* Elastic load balancer to mitigate slow loris attacks.
* AWS Shield with AWS WAF, a specialized defence tools to prevent sophisticated DOS attacks.
