For many users of Hong Kong servers, the biggest concern isn't bandwidth, network lines, or hardware, but rather sudden DDoS attacks. In cross-border businesses, high-traffic platforms, live-streaming e-commerce, or scenarios with frequent web scraping, sudden DDoS attacks are almost unavoidable risks. Especially in Hong Kong data centers, where bandwidth prices remain relatively high and the ecosystem is open, attacks can lead not only to network congestion and increased packet loss, but also to website lag, API delays, and even server crashes. More problematic is that if the attack peak exceeds the data center's protection threshold, it may trigger null routing and blackhole policies, rendering services inaccessible for extended periods. Therefore, learning to identify the source of attacks through logs and combining this with real-time firewall defense is an essential skill when using Hong Kong servers.
In actual operation and maintenance, the characteristics of sudden DDoS attacks are often quite obvious, such as a rapid surge in TCP connection counts, abnormal requests in Nginx access logs, system resources being exhausted by meaningless packets, and even SSH connection difficulties. However, what troubles many administrators is the constantly evolving nature of attacks. From classic SYN Flood and UDP Flood attacks to more insidious CC attacks, these attacks can occur in combination, making it difficult to diagnose problems immediately. However, regardless of the attack method, clues can always be found in the logs.
If the number of accesses from a particular IP address far exceeds normal business levels, such as thousands or even tens of thousands of accesses per minute, it can generally be identified as malicious requests. For web-based services, another typical sign is abnormal User Agent (UA), such as a crawler masquerading as a browser but requesting at a much higher frequency than normal users, or an empty UA field; this type of traffic is often part of an attack. For system-level attacks, such as SYN or UDP flood attacks, you can use netstat or ss to check if the connection status is abnormally concentrated in the SYN_RECV state. If the number is very large, it indicates that the server is experiencing a typical half-open connection attack. Through this log and system status analysis, operations and maintenance personnel can quickly determine whether the traffic is normal and rapidly initiate the protection phase.
After identifying the attack type, the most crucial step is to use a firewall for initial blocking. Hong Kong servers typically use Linux systems, allowing for rapid blocking using iptables or firewalld. If a single IP experiences a surge in requests, that IP can be blocked immediately. If the attacking IP range is too large, the entire network segment can be blacklisted.
For typical large-scale CC attacks, connection limits can reduce pressure. iptables provides connlimit and limit mechanisms, such as limiting the maximum concurrent connections of a single IP. These limits are effective in high-concurrency scenarios, preventing a single IP from masquerading as legitimate traffic to launch an attack. If the attack volume is larger and the sources are more dispersed, such as a UDP flood attack that aims to saturate bandwidth, specific ports or protocols should be disabled to reduce overhead. While this strategy may impact some business functions, it can effectively reduce unnecessary traffic and prevent server downtime in emergencies. For smaller attacks, firewalld's rich rules configuration is more convenient.
Besides manually blocking IPs, using fail2ban for automated blocking is also a common approach. It can identify abnormal access based on logs and automatically blacklist IPs, reducing manual intervention and improving the server's self-defense capabilities. Especially for businesses operating in Hong Kong data centers, fail2ban combined with Nginx rate limiting can effectively reduce the pressure from CC attacks.
This type of rate limiting strategy does not affect the normal user experience but effectively weakens the impact of malicious traffic. However, when facing larger-scale and more complex attacks, relying solely on the server's own firewall may be insufficient; it requires the use of data center-level DDoS protection, such as Hong Kong CN2 DDoS protection, premium network DDoS protection, and mainland China backhaul DDoS protection. Data center-level protection can maintain network stability under attacks of tens or even hundreds of Gbps and is considered an essential solution for handling large-scale attacks. If the attack traffic is found to significantly exceed the server's bandwidth and is beyond the server's capacity, promptly contacting the data center to activate DDoS protection or temporary capacity expansion is a crucial step to ensure uninterrupted business operations.
However, many administrators misjudge the source of the problem when encountering an attack, assuming that latency or lag is caused by the attack, when in fact it is a false alarm caused by insufficient server performance, SSD I/O bottlenecks, full bandwidth utilization, or routing jitter. Therefore, when judging an attack, it is essential to simultaneously observe bandwidth monitoring, CPU usage, system load, packet loss rate, and route tracing.
If some nodes experience packet loss, but the final node does not, it's usually not an attack, but rather normal network load. This is more common on Hong Kong servers due to frequent congestion on cross-border links. Only when bandwidth spikes significantly, connection counts are abnormal, and logs show a large number of duplicate requests can a more accurate diagnosis of a malicious attack be made.
Improving overall defense capabilities requires more than just emergency blocking; establishing stable, long-term protection strategies is crucial. For example, enabling CDN for business operations to offload static resources or high-traffic requests to edge nodes; enabling WAF for dynamic businesses to automatically identify and block SQL injection, brute-force attacks, and malicious scripts at the web layer; and adding authentication mechanisms such as signatures and tokens to API services to reduce unnecessary external access. For high-risk businesses, restricting access from foreign IP addresses and non-whitelisted regions can further reduce the probability of attacks. Because of their high degree of openness, Hong Kong servers attract many scanners, crawlers, and testing scripts; therefore, proactively building a protection system is far more effective than passively handling attacks.
In high-security scenarios, log analysis capabilities are particularly important. Regularly backing up logs, synchronizing logs to external servers, and visualizing them using ELK or Grafana make abnormal access trends easily identifiable. For example, integrating Nginx logs with ELK allows you to see the upward trend of access volume from a single IP address on a chart, automatically alerting you in the early stages of an attack. Combined with alerting systems administrators can be notified in the first second of a traffic spike, preventing the impact from escalating. Moving from reactive response to proactive defense is a crucial step in maturing server security capabilities.
