AWS - Security Groups

• Security Group is a virtual firewall.
• One instance can have multiple security groups.
• All inbound traffic is blocked by default 
• All outbound traffic is allowed by default.
• Changes to security groups take effect immediately.
• Any number of EC2 instances can be attached to a Security Group.
• EC2 instances can be attached to multiple security groups.
• Security groups are STATEFUL
• If you create an inbound rule allowing traffic in, that traffic is immediately allowed out.
• You can NOT block specific IP addresses using security groups, instead to block traffic use Network Access Control Lists (NACL)
• You can only specify allow rules but not deny rules.