The answer is that the Redshift cluster’s security group lacks an inbound rule allowing TCP traffic on port 5439 from the EC2 instance. This is correct because while ICMP (ping) can reach the EC2 instance, indicating the network path and VPC routing are functional, the specific port required for Redshift connectivity—5439—is being blocked at the security group level. On the AWS Certified Data Engineer Associate DEA-C01 exam, this scenario tests your understanding of security group stateful filtering versus network ACLs and common misconfigurations in same-VPC setups. A frequent trap is assuming ping success means all traffic is allowed, but security groups act as a virtual firewall for each resource, and inbound rules must explicitly permit the application port. Remember the mnemonic: “Ping is not a port—ICMP works, TCP 5439 might not.”
DEA-C01 Data Store Management Practice Question
This DEA-C01 practice question tests your understanding of data store management. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
Network Topology
Refer to the exhibit. A data engineer needs to connect to the Redshift cluster from an EC2 instance in the same VPC. The engineer can ping the EC2 instance but cannot connect to Redshift using the endpoint address and port 5439. What is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The security group for the Redshift cluster does not allow inbound traffic on port 5439 from the EC2 instance.
The most likely cause is that the security group associated with the Redshift cluster does not have an inbound rule allowing TCP traffic on port 5439 from the security group or IP address of the EC2 instance. Since the engineer can ping the EC2 instance (ICMP works), but cannot connect to Redshift on port 5439, this points to a firewall or security group rule blocking the specific port, not a network reachability issue.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
The security group for the Redshift cluster does not allow inbound traffic on port 5439 from the EC2 instance.
Why this is correct
Security group rules must permit the connection.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The Redshift cluster is in a different VPC.
Why it's wrong here
Both are in same VPC (VpcId is same).
✗
The Redshift cluster is not in an available state.
Why it's wrong here
Cluster status is available.
✗
The Redshift cluster is publicly accessible and requires an internet gateway.
Why it's wrong here
Cluster is not publicly accessible.
Common exam traps
Common exam trap: answer the scenario, not the keyword
AWS often tests the distinction between ICMP reachability (ping) and TCP port-level connectivity, leading candidates to overlook security group rules when they see successful ping results.
Detailed technical explanation
How to think about this question
Redshift uses PostgreSQL wire protocol on port 5439, and security groups act as a virtual firewall controlling inbound and outbound traffic at the instance level. Even if network ACLs (stateless) allow traffic, a security group (stateful) must explicitly permit the inbound connection from the source (EC2 instance). In real-world scenarios, engineers often forget to add the EC2 security group as a source in the Redshift inbound rule, leading to this exact symptom.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Data Store Management — This question tests Data Store Management — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The security group for the Redshift cluster does not allow inbound traffic on port 5439 from the EC2 instance. — The most likely cause is that the security group associated with the Redshift cluster does not have an inbound rule allowing TCP traffic on port 5439 from the security group or IP address of the EC2 instance. Since the engineer can ping the EC2 instance (ICMP works), but cannot connect to Redshift on port 5439, this points to a firewall or security group rule blocking the specific port, not a network reachability issue.
What should I do if I get this DEA-C01 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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