What solution should a cloud architect implement to isolate traffic between subnets in an IaaS platform while allowing stateful communication?

To achieve isolation of traffic between subnets while allowing stateful communication in an Infrastructure as a Service (IaaS) platform, implementing security groups is the most suitable solution. Security groups act as virtual firewalls that control inbound and outbound traffic to resources (such as virtual machines) within cloud services.

When configured, security groups can specify rules that allow or deny traffic based on IP addresses, protocols, and ports. One significant advantage is that security groups are stateful, meaning if a request is allowed in one direction, the response is automatically allowed in the opposite direction. This property is crucial for maintaining seamless communication between resources while ensuring that only authorized traffic can flow between different subnets.

In contrast, network access control lists (ACLs) offered other choices provide a level of control but are stateless, meaning any allowed traffic must have a corresponding return rule explicitly defined. Host Intrusion Prevention System (HIPS) and Intrusion Detection System (IDS) policies focus more on security monitoring and reactions to potential threats rather than managing active communication between diverse network segments.

By utilizing security groups, the cloud architect can effectively manage the flow of traffic, ensuring both isolation and the necessary communication between subnets.