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Cloud Computing · Foundational

Security Group (SG)

Stateful virtual firewall attached to instances or network interfaces that allows specified inbound and outbound traffic.

Definition

AWS security groups contain only allow rules; return traffic is automatically permitted because they are stateful. Rules can reference CIDR ranges, prefix lists or other security groups, enabling tier-based rules without IP addresses. By default, inbound traffic is denied and outbound is allowed. Azure network security groups and OCI network security groups are similar constructs.

Example

The database security group allows TCP 3306 only from the application tier's security group ID.

Exam tip

Security groups are stateful and allow-only; network ACLs are stateless and support explicit deny rules.

Don't confuse it with

Related terms