An organization's Amazon EC2 instances located in a private subnet are experiencing connec… — AWS Certified SysOps Administrator - Associate

An organization's Amazon EC2 instances located in a private subnet are experiencing connection timeouts when trying to access Amazon S3. A Gateway VPC Endpoint for Amazon S3 has been deployed and linked to the private subnet's route table. The instances use a security group that permits all egress traffic. The subnet's custom Network ACL has an egress rule allowing port $443$ traffic to the S3 prefix list, but all custom ingress rules have been removed, leaving only the default deny rule. What configuration change is necessary to restore access to Amazon S3?

A
Update the route table of the private subnet to direct traffic destined for $0.0.0.0/0$ to an Internet Gateway.
B
Dissociate the Gateway VPC Endpoint from the private subnet's route table and associate it with the public subnet's route table.
Configure an inbound rule in the custom Network ACL to allow traffic from the Amazon S3 prefix list on ephemeral ports $1024$ - $65535$ .Cevap
D
Route the S3 traffic through a NAT Gateway located in a different Availability Zone to bypass local subnet routing restrictions.

Cevap

Configure an inbound rule in the custom Network ACL to allow traffic from the Amazon S3 prefix list on ephemeral ports

1024

65535

Network ACLs are stateless, meaning both inbound and outbound traffic must be explicitly permitted. While the security group automatically tracks states, the custom Network ACL requires a return rule. S3 response traffic uses ephemeral ports

1024

65535

, so adding an inbound rule in the Network ACL for this range resolves the connection timeout.

Adım Adım Çözüm

Analyze the network route configuration for S3 traffic.

The route table is already associated with the S3 Gateway VPC Endpoint, indicating that the routing layer is correctly configured to redirect S3 traffic through the gateway endpoint.

Before troubleshooting security controls, verifying that a route to the target destination exists ensures routing is correct.

Examine the stateful and stateless security configurations.

The security group is stateful and permits outbound traffic, which automatically allows return traffic. The custom Network ACL is stateless and only contains an outbound rule for port

443

, meaning inbound response traffic is blocked by the default deny rule.

Since Network ACLs are stateless, they evaluate inbound and outbound traffic independently. Ephemeral ports must be opened for return traffic.

Identify the appropriate source and port range for the inbound rule.

Configure the inbound rule with the source as the S3 prefix list and the port range as ephemeral ports

1024

65535

S3 initiates connections back to the client using ephemeral ports, so the stateless return path must permit this range.

Anahtar Kavram

Stateless nature of Network Access Control Lists (NACLs) and ephemeral port requirements for return traffic

Tahmini Süre:2m 30s

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Cevap

Adım Adım Çözüm

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