A security group is a collection of network access rules known as security group rules that limit the types of traffic an instance can send or receive. When an iptables-based driver is used, security group rules are converted to iptables rules that are applied on the compute nodes hosting the instances. Each OpenStack project is provided with a default security group that can be modified by users within the project. OpenStack Networking provides an API for creating, modifying, applying, and deleting security groups and rules.
There are multiple ways to apply security groups to instances. For example, one or more instances, usually of similar functionality or role, can be placed in a security group. Security group rules can reference IPv4 and IPv6 hosts and networks as well as other security groups. Referencing a particular security group in a rule...