Free Amazon SCS-C03 Exam Dumps June 2026

Amazon EC2 security groups are stateful, meaning that once a connection is established, return traffic is automatically allowed, even if the inbound rule that originally permitted the connection is later removed. According to the AWS Certified Security -- Specialty Official Study Guide and Amazon EC2 security documentation, existing connections are not terminated when security group rules change. This explains why the SSH session remains active even after the security group rules were modified, while new traffic such as ICMP ping is blocked.

To immediately and fully isolate an EC2 instance during an incident response scenario, AWS recommends using stateless network controls. Amazon VPC network ACLs (NACLs) are stateless, which means that every packet is evaluated against the ACL rules regardless of whether the traffic is part of an existing connection. When a deny rule is added, all traffic is immediately blocked, including active sessions.

By creating a network ACL and associating it with the subnet that contains the target instance, and by adding explicit deny rules with the lowest rule numbers for both inbound and outbound traffic, the security engineer ensures that all network communication to and from the instance is immediately interrupted. This approach satisfies the requirement to isolate the instance while preserving its runtime state and memory for forensic analysis.

Other options fail to meet the requirement because security group modifications do not terminate existing sessions, Systems Manager does not enforce network isolation, and host-level firewall changes require instance-level access and do not provide immediate, network-enforced isolation.

AWS Certified Security -- Specialty Official Study Guide

Amazon EC2 Security Groups Documentation

Amazon VPC Network ACL Documentation

AWS Incident Response Best Practices

AWS best practices recommend using a shared secret header between CloudFront and ALB origins to prevent direct access. CloudFront injects a custom header, and the ALB listener rules validate its presence.

IP-based controls are brittle due to CloudFront IP changes. PrivateLink and internal ALBs are not supported as CloudFront origins. Header validation is the most reliable and widely recommended pattern.

Referenced AWS Specialty Documents:

AWS Certified Security -- Specialty Official Study Guide

CloudFront Origin Protection

AWS WAF and ALB Integration

Amazon CloudWatch Logs is designed to collect, store, and analyze log data from ephemeral compute resources such as EC2 instances in Auto Scaling groups. According to the AWS Certified Security -- Specialty Study Guide, using the CloudWatch agent to stream logs off instances ensures log durability even when instances are terminated during scale-in events.

CloudWatch Logs Insights provides a fully managed, serverless query engine that enables ad hoc querying, filtering, and aggregation of log data without requiring additional infrastructure. This directly satisfies the requirement to query logs for application sessions and user troubleshooting.

Option A introduces operational risk because logs could be lost between cron executions. Option B requires additional services and data pipelines, increasing cost and complexity. Option E adds storage cost and management overhead and is not necessary for log analytics.

AWS best practices recommend CloudWatch Logs and Logs Insights as the most cost-effective and scalable solution for centralized log retention and analysis in Auto Scaling environments.

Referenced AWS Specialty Documents:

AWS Certified Security -- Specialty Official Study Guide

Amazon CloudWatch Logs and Logs Insights

AWS Logging Best Practices

AWS networking best practices require private subnets to access the internet only through NAT gateways located in public subnets. According to the AWS Certified Security -- Specialty Study Guide, NAT gateways must be provisioned in public subnets and used as the default route for outbound traffic from private subnets.

Verifying NAT gateways in each Availability Zone ensures high availability and fault tolerance. Updating the private subnet route tables to send 0.0.0.0/0 traffic to the NAT gateway prevents direct internet access while allowing outbound connectivity.

Routing private subnet traffic directly to an internet gateway violates subnet isolation principles. NAT gateways must never be placed in private subnets.

Referenced AWS Specialty Documents:

AWS Certified Security -- Specialty Official Study Guide

Amazon VPC Routing and NAT Gateways

AWS Network Segmentation Best Practices