There is no denying that fact that you can take steps which can reduce the impact of a DDoS attack but you can not guarantee complete protection against DDoS attacks. There is a reason for it. DDoS attacks just replace malicious traffic with legitimate traffic. Since most servers lack the mechanism to differentiate legitimate traffic from malicious traffic, they fall victim to DDoS attacks. Thankfully, you can still mitigate the risk to a certain degree by investing in cheap DDoS protection.