> For the complete documentation index, see [llms.txt](https://dev7days.gitbook.io/dev7days/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://dev7days.gitbook.io/dev7days/aws/ec2/security-group.md). # Security Group It is a network security that can attach to AWS service acting as a `firewall`. Security group control how traffic is allowed into AWS service. There are 2 part that need to define to control traffic 1. Inbound rule 2. Outbound rule \ **Inbound Rule** It is the rule defined traffic that allow to access this service. by default It is not allow to access AWS service. \ **Outbound Rule** It is the rule defined traffic that allow service to go outside. by default It allows to use any port to go outside. Example **Remark** * One `Security Group` can be attached to multiple instance * Locked down to region (If you change the region then you need to create a new one) * It is the component that live outside EC2 (If traffic is blocked the EC@ instance won't see it) * If applcation is not accessible then it is security group issue (timeout error) * If aplication gives a `connection refused` (application error -> not related security group)