SAA-C03 Design Secure Architectures Practice Question
Exhibit
Network design excerpt: VPC: 10.40.0.0/16 Private subnet route table: - 10.40.0.0/16 local - 0.0.0.0/0 -> nat-0c91f2a7d3b1e3 Instance behavior: - patching scripts fail when downloading packages from S3 - AWS Systems Manager Session Manager shows: 'Target not connected' - Security team wants to remove NAT gateway usage for these workloads
Based on the exhibit, what is the best way to let private EC2 instances reach Amazon S3 and AWS Systems Manager without sending traffic through the internet or a NAT gateway?
⚠ Common exam trap
Many candidates assume all AWS services can be accessed via a single endpoint type, but S3 requires a gateway endpoint (route table-based) while Systems Manager and its sub-services require interface endpoints (PrivateLink-based), and failing to create all three (including EC2Messages and SSMMessages) will break Systems Manager functionality.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Create a gateway endpoint for S3 and interface endpoints for Systems Manager, EC2Messages, and SSMMessages.
Gateway endpoints for S3 allow private EC2 instances to access S3 via AWS's private network without traversing the internet or a NAT gateway, using prefix lists and route table entries. Interface endpoints for Systems Manager, EC2Messages, and SSMMessages provide private connectivity to AWS Systems Manager via PrivateLink, enabling secure instance management without public IPs or NAT.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Create a gateway endpoint for S3 and interface endpoints for Systems Manager, EC2Messages, and SSMMessages.
Why this is correct
This keeps traffic on the AWS network and avoids NAT or internet traversal. S3 uses a gateway endpoint, while Systems Manager needs interface endpoints for the control and messaging services that Session Manager depends on. It directly addresses both the S3 download problem and the missing Session Manager connectivity in a private subnet design.
- ✗
Add a more permissive security group rule allowing outbound 0.0.0.0/0 on all ports.
Why it's wrong here
Security group rules are evaluated after routing decisions, so adding an outbound 0.0.0.0/0 rule does not provide a path to the internet or to AWS services. Without a route through a NAT gateway/internet gateway or a VPC endpoint, traffic is still dropped. Moreover, Systems Manager requires interface endpoints for each service, and S3 requires a gateway endpoint or NAT; a permissive SG alone cannot enable these private connections.
When this WOULD be correct
This option would be correct in a scenario where the question asks for the simplest way to allow outbound internet access from private EC2 instances, without any restriction on using the internet or NAT gateway, and the goal is just to enable general outbound connectivity.
- ✗
Replace the NAT gateway with a network ACL that allows ephemeral ports to the internet.
Why it's wrong here
A network ACL is a stateless packet filter, not a routing or connectivity construct. Even if you allow ephemeral ports, the subnet has no route to an internet gateway or NAT device, so outbound traffic cannot leave the VPC. Additionally, Session Manager and S3 access in a private subnet rely on VPC endpoints or NAT, and NACLs cannot create those private connections.
When this WOULD be correct
If the question asked how to restrict outbound traffic from a public subnet to the internet using only network ACLs (e.g., allow ephemeral ports while blocking other traffic), then replacing a NAT gateway with a properly configured network ACL could be correct, assuming instances have public IPs or are behind an internet gateway.
- ✗
Move the instances to public subnets so they can reach AWS services directly.
Why it's wrong here
Moving instances to public subnets would route S3 and Systems Manager traffic through an internet gateway, violating the requirement to keep traffic on the AWS private network. Public subnets also assign public IPs and expose instances to inbound internet traffic, increasing the attack surface. A private subnet with VPC endpoints is the correct way to reach these AWS services without traversing the internet.
When this WOULD be correct
If the question asked for the simplest way to allow instances to reach the internet (not just AWS services) without a NAT gateway, and security concerns were not a factor, moving instances to public subnets with public IPs and appropriate security groups would enable direct internet access.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The SAA-C03 exam frequently reuses these exact scenarios with slightly different constraints.
✓Create a gateway endpoint for S3 and interface endpoints for Systems Manager, EC2Messages, and SSMMessages.Correct answer▾
Why this is correct
This keeps traffic on the AWS network and avoids NAT or internet traversal. S3 uses a gateway endpoint, while Systems Manager needs interface endpoints for the control and messaging services that Session Manager depends on. It directly addresses both the S3 download problem and the missing Session Manager connectivity in a private subnet design.
✗Add a more permissive security group rule allowing outbound 0.0.0.0/0 on all ports.Wrong answer — click to see why▾
Why this is wrong here
This option does not address the requirement to avoid sending traffic through the internet or a NAT gateway; a permissive security group rule still routes traffic via the internet or NAT gateway, not through private VPC endpoints.
★ When this WOULD be the correct answer
This option would be correct in a scenario where the question asks for the simplest way to allow outbound internet access from private EC2 instances, without any restriction on using the internet or NAT gateway, and the goal is just to enable general outbound connectivity.
Why candidates choose this
Candidates may think that allowing all outbound traffic via a security group is a quick fix, overlooking the specific requirement to avoid internet or NAT gateway paths and the need for private connectivity via endpoints.
✗Replace the NAT gateway with a network ACL that allows ephemeral ports to the internet.Wrong answer — click to see why▾
Why this is wrong here
Network ACLs cannot replace NAT gateways for outbound internet access; they are stateless and only filter traffic, not provide NAT. Private instances still need a NAT device to reach the internet, and Systems Manager requires VPC endpoints, not just internet access.
★ When this WOULD be the correct answer
If the question asked how to restrict outbound traffic from a public subnet to the internet using only network ACLs (e.g., allow ephemeral ports while blocking other traffic), then replacing a NAT gateway with a properly configured network ACL could be correct, assuming instances have public IPs or are behind an internet gateway.
Why candidates choose this
Candidates may confuse network ACLs with NAT gateways, thinking ACLs can provide outbound connectivity by allowing ephemeral ports, or they may underestimate the need for NAT to translate private IPs.
✗Move the instances to public subnets so they can reach AWS services directly.Wrong answer — click to see why▾
Why this is wrong here
Moving instances to public subnets exposes them directly to the internet, which violates the requirement to avoid sending traffic through the internet. Private instances should remain in private subnets and use VPC endpoints for secure, private connectivity to AWS services.
★ When this WOULD be the correct answer
If the question asked for the simplest way to allow instances to reach the internet (not just AWS services) without a NAT gateway, and security concerns were not a factor, moving instances to public subnets with public IPs and appropriate security groups would enable direct internet access.
Why candidates choose this
Candidates may think that public subnets provide direct access to all AWS services, overlooking that public subnets still route traffic through the internet, and that private connectivity via VPC endpoints is more secure and cost-effective for services like S3 and Systems Manager.
Analysis generated from the official SAA-C03blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Visual reference
Quick reference
AWS S3 Storage Class Comparison
| Storage Class | Min Duration | Retrieval | Use Case |
|---|---|---|---|
| S3 Standard | None | Immediate | Frequently accessed data |
| S3 Standard-IA | 30 days | Immediate | Infrequent access, rapid retrieval |
| S3 One Zone-IA | 30 days | Immediate | Non-critical infrequent data |
| S3 Intelligent-Tiering | None | Immediate–hours | Unknown or changing access patterns |
| S3 Glacier Instant | 90 days | Milliseconds | Archive with instant retrieval |
| S3 Glacier Flexible | 90 days | Minutes–hours | Archive, flexible retrieval |
| S3 Glacier Deep Archive | 180 days | Hours | Long-term compliance archive |
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This SAA-C03 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the SAA-C03 exam.