Security Group
A security group is a stateful virtual firewall that controls traffic to resources.
Updated: 2026-03-05
Definition
A security group controls inbound and outbound traffic rules for resources like instances.
Stateful means return traffic is automatically allowed when a connection is permitted.
Key points
- Stateful filtering
- Usually attached to instances/resources
- Rules are allow-based (no explicit deny in some platforms)
Common mistakes
- Opening wide ports to the world for convenience.
- Confusing security groups with NACLs (different behavior/scope).
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