Security group as virtual firewall in AWS - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a security group in AWS?

A security group is like a virtual firewall that controls the traffic allowed to reach your AWS resources, such as EC2 instances. It filters incoming and outgoing network traffic based on rules you set.

beginner

How do security groups control traffic?

Security groups control traffic by using rules that specify allowed protocols, ports, and source or destination IP addresses. Only traffic matching these rules is allowed; everything else is blocked.

intermediate

Can security groups block outgoing traffic by default?

No. By default, security groups allow all outgoing traffic. You must add specific rules to restrict outbound traffic if needed.

beginner

What happens if you don’t add any inbound rules to a security group?

If no inbound rules exist, no incoming traffic is allowed to the resource. This means the resource is effectively isolated from incoming network connections.

intermediate

How are security groups different from network ACLs in AWS?

Security groups act as virtual firewalls at the instance level and are stateful, meaning return traffic is automatically allowed. Network ACLs operate at the subnet level and are stateless, requiring explicit rules for both inbound and outbound traffic.

What type of traffic does a security group control in AWS?

A Inbound and outbound traffic

B Only inbound traffic

C Only outbound traffic

D Traffic between AWS regions

Security groups control both inbound and outbound traffic based on rules you define.

By default, what is the outbound traffic rule in a new security group?

A Only SSH traffic is allowed

B All outbound traffic is blocked

C Only HTTP traffic is allowed

D All outbound traffic is allowed

New security groups allow all outbound traffic by default.

If you want to allow SSH access to an EC2 instance, which port should you open in the security group inbound rules?

A Port 80

B Port 22

C Port 443

D Port 3389

SSH uses port 22, so you must allow inbound traffic on port 22.

What does it mean that security groups are stateful?

A Return traffic is automatically allowed

B Rules must be set for both inbound and outbound separately

C They only work within one AWS region

D They log all traffic automatically

Stateful means if inbound traffic is allowed, the response outbound traffic is automatically allowed without extra rules.

Can you assign multiple security groups to a single EC2 instance?

A Only if the instance is in a public subnet

B No, only one security group per instance

C Yes, multiple security groups can be assigned

D Only for instances running Windows

You can assign multiple security groups to an EC2 instance to combine rules.

Explain how a security group acts as a virtual firewall in AWS.

Think about how a firewall filters traffic to protect a computer.

Describe the difference between security groups and network ACLs in AWS.

Consider where and how each controls traffic.