What are security groups and what do they regulate?

Difficulty: 5/10

inbound/outbound rules, stateful firewall, VPC integration

Understanding AWS Security Groups

A security group acts as a virtual firewall for your EC2 instances to control incoming and outgoing traffic. Unlike network ACLs, security groups are stateful; if you send a request from your instance, the response traffic for that request is allowed to flow in regardless of inbound security group rules.

Traffic Regulation

1
Inbound Traffic: Filters traffic coming into the instance based on protocol, port range, and source IP/Security Group.
2
Outbound Traffic: Filters traffic leaving the instance to specific destinations.
3
Default Deny: By default, all inbound traffic is blocked until you add allow rules.
4
Stateful Filtering: Automatically allows return traffic for established connections.

Scenario Questions

0-2 years experience

1You need to allow SSH access to a newly launched EC2 instance from your office IP. How would you configure the security group?
2If you attach two security groups to an instance, one allowing inbound HTTP and another allowing inbound HTTPS, what inbound traffic will be permitted?
3What happens to outbound traffic if you remove all outbound rules from a security group attached to an instance?

Follow-up Questions

How would you verify that your security group changes took effect?
What are the limits on security groups per VPC, and how do you work around them?
Can you explain the difference between security groups and network ACLs in this context?