Firewall is the first security guarantee of Singapore cloud server, reasonable and rigorous configuration of Singapore cloud server firewall can better resist external attacks and ensure business continuity. However, many users' cognition of the firewall still stays on the port opening and closing, ignoring policy setting, rule priority, traffic monitoring, and so on. In this way, configuration vulnerabilities may occur, such as extortion attacks caused by database port exposure and service exceptions caused by rule conflicts.

The cloud server firewall system consists of two levels, one is the Security Group or network ACL (access control list) provided by the cloud service provider, the other is the operating system's own firewall tools (such as iptables, firewalld), the two work together to form a three-dimensional protection network. Incorrect configuration may cause rule conflicts or protection blind spots.

Protocol and port management are the basis of firewall configuration, which hides many risks. Many users directly copy the "generic rule template" in the network, such as allowing all ICMP protocols to be used for network diagnostics, but this may provide an attacker with a channel to detect the server's survival status. The right approach is fine-grained control - if ICMP responses are required, limit them to a specific IP segment (such as the office network IP of the operations team) rather than 0.0.0.0/0. For Web servers, in addition to port 80/443, you need to be alert to the exposure of management ports (such as MySQL 3306 and Redis 6379).

The rule priority problem is often underestimated, but it directly affects the actual behavior of the firewall. Using iptables as an example, rules are matched from top to bottom. Once a rule is matched, subsequent rules are not executed. If "Allow all traffic from 192.168.1.0/24" is set at the top of the chain and "Deny all TCP traffic" is set at the bottom of the chain, the former overrides the latter, causing the denial policy to become invalid. This problem is particularly acute in complex business scenarios, such as servers running both Web services and internal apis, where it is important to ensure that high-priority rules precisely match business requirements. You are advised to adopt whitelist hierarchical design: All traffic is denied first, and then permission rules are added one by one by service module. For example, Layer 1 allows the health check IP of the load balancer, Layer 2 opens the Web service port, and Layer 3 allows the specific IP of the internal management system to access SSH. This structure not only avoids rule conflicts, but also improves maintainability.

Firewall configuration in containerized environment faces new challenges. With the popularity of Kubernetes, traffic isolation between the container network and the host network has become a must. If the host firewall rules are used directly, communication between containers may be blocked. For example, Docker creates a virtual bridge docker0 by default and inserts rules into iptables to manage container traffic. Blindly modifying the iptables rules of the host can break Docker's network policy. The right approach is to define the access rules for container groups through a container orchestration tool, such as Kubernetes NetworkPolicy, or use a CNI plug-in, such as Calico, for fine-grained control. In addition, ensure that the firewall of the host permits ports required by the container network (for example, Kubernetes API Server 6443 and NodePort range 30,000-32767) to prevent service unavailability due to rule conflicts. The backup and rollback mechanism of firewall configuration is often neglected, but it can save the business at a critical time.

The cloud server firewall configuration needs to be dynamically optimized based on the network architecture, service features, and threat situation. From rule priority design to log analysis, from container network adaptation to automated management, security needs to be considered at every step.