The overseas cloud server security group is a virtual firewall provided by the cloud platform. It mainly acts at the instance level and controls inbound and outbound traffic through refined rules. Unlike traditional hardware firewalls, the security group has stateful detection capabilities - automatically allowing return traffic of established connections without configuring two-way rules. For example, after the inbound TCP 22 port (SSH) is released, the outbound response data will be automatically released. This design binds security policies to instances to achieve dynamic protection and becomes the first line of defense for cloud environment network security.

1. Security Group Core Mechanism and Configuration Process

Analysis of Rule Structure: Each security rule of the overseas cloud server security group includes 6 key elements, including protocol type, supporting TCP, UDP, ICMP (v4/v6) and GRE, among which ICMP protocol has no port concept; port range, TCP/UDP protocol needs to specify port 165535 (such as SSH uses 22, MySQL uses 3306); address object, inbound rules define source IP (such as 192.168.1.0/24), outbound rules define target IP; action strategy, mainly "accept" or "reject" traffic; priority, such as high priority rules take precedence, and precise rules take precedence under the same priority; direction control includes distinguishing inbound (ingress) and outbound (egress) traffic.

Four-step configuration process

1. Create a security group

Avoid selecting the "open all ports" template (high risk), it is recommended to use the minimum open template (such as releasing ports 22/80/443).

2. Configure rules

Inbound rules: control the traffic of external access to the instance (such as opening port 80 for Web access)

Outbound rules: allow all outbound traffic by default, and sensitive businesses can limit the target IP (such as only allowing access to cloud storage service IP)

Example: Database security group inbound rules

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Protocol: TCP | Port: 3306 | Source address: Web server security group ID | Action: Accept

3. Associate instances

A single server can be bound to multiple security groups (rule overlap), but it is recommended not to exceed 5 to avoid rule conflicts.

4. Real-time validation

Rule changes usually take effect within 12 minutes. Inbound rules reset existing connections, and outbound rules only affect new connections.

2. Key considerations and best practices

Three principles of security configuration: The principle of least privilege is to prohibit opening 0.0.0.0/0 to the management port (such as SSH 22) and the database port (3306/1433) only to the application server; the principle of layered defense architecture

mermaid
graph TB
A[Network layer] >|VPC isolation| B[Subnet layer]
B >|Network ACL| C[Instance layer]
C >|Security group| D[Host firewall]

Combining network ACL (subnet-level stateless filtering) and security group (instance-level stateful filtering) to build in-depth defense. The last one is dynamic authorization management, using security group ID instead of IP authorization (such as allowing WebSG to access DBSG), adapting to instance IP changes, production environment configuration change approval process, and enabling security group operation audit.

Typical scenario configuration

3. Advanced applications and troubleshooting

Performance optimization techniques include connection tracking management, ICMP protocol connection aging time is 30 seconds, TCP established connection (ESTABLISHED) aging time is 600 seconds, and multiple rules with the same source/same port can be merged in rule merging (such as TCP:80,443 instead of two independent rules) to avoid rule flooding. A single security group does not exceed 100 rules to prevent performance degradation.

Common troubleshooting

1. The rule is not effective

Check whether the security group is associated with the instance network card and use telnet <IP> <port> to test connectivity.

2. Implicit Deny Trap

The security group denies all traffic that is not explicitly allowed by default. Check whether necessary ports are missed.

3. OS Firewall Conflict

If access is still not possible after the security group is released, check the iptables/firewalld configuration in the instance.

4. Architecture Evolution and Cost Control

The hybrid cloud scenario uses security groups to achieve controlled mutual access between IDC and overseas cloud servers, replacing traditional private networks. Automated management uses cloud platform APIs to dynamically adjust rules. TCO optimization reuses security group templates to reduce configuration time, and large enterprises can save 30% of operation and maintenance costs.

The security group is not a "configure and forget" tool. According to Gartner statistics, 70% of cloud security incidents are caused by incorrect configuration. Follow the principle of "least privilege + layered defense", audit rules regularly (recommended once a month), and use the cloud platform's security group traffic log to analyze abnormal access. In the scenarios of 2.0 or GDPR compliance, the refined control capabilities of the security group are the core support for meeting network security audit requirements.