The best way to detect that a distributed denial of service (DDoS) attack is occurring is to use automated monitoring of logs. A DDoS attack disrupts the operations of a server, service, or network byflooding it with unwanted Internet traffic2. Automated monitoring of logs can help pinpoint potentialDDoS attacks by analyzing network traffic patterns, monitoring traffic spikes or other unusual activity, and alertingadministrators or security teams of any anomalies or malicious requests, protocols, or IP blocks3. Automated monitoring of logs can also help identify the source, type, and impact of the DDoS attack, and provide evidence for further investigation or mitigation.

The other options are not as effective as automated monitoring of logs for detecting DDoS attacks. Customer service complaints are an indirect and delayed indicator of a DDoS attack, as they rely onusers reporting problems with accessing a website or service. Customer service complaints may also be caused by other factors unrelated to DDoS attacks, such as server errors or network issues. Server crashes are an extreme and undesirable indicator of a DDoS attack, as they indicate that the server has already been overwhelmed by the attack and has stopped functioning. Server crashes may also result in data loss or corruption, service disruption, or reputational damage. Penetration testing is a proactive and preventive measure for assessing the security posture of a system or network, but it does not detect ongoing DDoS attacks. Penetration testing may involve simulating DDoS attacks to test the resilience or vulnerability of a system or network, but it does not monitor real-time traffic or identify actual attackers.