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Question 1,306 of 1,786

Data Operations and Support →hardMultiple ChoiceObjective-mapped

Quick Answer

The answer is to change the subnet of the Glue job to one with a larger CIDR range, such as /20 instead of /24. This is correct because the random timeout errors when connecting to RDS are caused by subnet IP exhaustion: AWS Glue dynamically allocates elastic network interfaces (ENIs) in the subnet, and a /24 subnet only provides 251 usable IPs, which can be quickly consumed by concurrent Glue workers, leaving no available IP for new connections. On the AWS Certified Data Engineer Associate DEA-C01 exam, this scenario tests your understanding of how Glue’s VPC networking consumes IP addresses and that connection timeouts are often a network-layer issue, not a database or security group problem. A common trap is to assume the security group is misconfigured or to increase retries, but the root cause is insufficient IP capacity. Memory tip: think “Glue needs IPs, not retries”—if your subnet is too small, scale the CIDR, not the timeout.

DEA-C01 Data Operations and Support Practice Question

This DEA-C01 practice question tests your understanding of data operations and support. 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.

A data engineering team uses AWS Glue ETL jobs to process daily data from an Amazon RDS for PostgreSQL instance into Amazon S3. Recently, the jobs have been failing randomly with the error 'psycopg2.OperationalError: could not connect to server: Connection timed out'. The RDS instance is in a private subnet with a security group that allows inbound traffic from the Glue job's security group on port 5432. The Glue job is configured to use the same VPC, subnet, and security group. The RDS instance has sufficient connections and is not at CPU or memory limits. The failures occur at different times each day, and the job works when retried immediately. Which action should the team take to resolve the issue?

Clue words in this question

Noticing these words before you look at the options changes how you read each choice.

Clue: "immediately / without restart"
Why it matters: Time or reboot constraint — the correct answer must take effect right away without requiring a reboot or reload.

Question 1hardmultiple choice

Review the full subnetting walkthrough →

A
Set the Glue job timeout to 60 minutes to ensure the job does not fail prematurely.
Why wrong: The error indicates a connection timeout, not a job timeout; increasing job timeout does not fix network connectivity.
B
Change the subnet of the Glue job to one with a larger CIDR range (e.g., /20 instead of /24).
A larger subnet provides more available IP addresses, reducing the chance of exhausting the pool for Glue ENIs.
C
Add an inbound rule to the RDS security group allowing traffic on ports 1024-65535 from the Glue security group.
Why wrong: PostgreSQL uses port 5432; ephemeral ports are not required for this connection.
D
Increase the number of retries in the Glue job configuration to 5.
Why wrong: Retries do not address the root cause of network connectivity failures.

Full breakdown with real-world context →

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

✓

Change the subnet of the Glue job to one with a larger CIDR range (e.g., /20 instead of /24).

Option B is correct because the timeout suggests network connectivity issues, likely due to Glue's dynamic IP allocation exhausting available IP addresses in the subnet's CIDR range, which causes connection failures when no IP is available. Resizing the subnet to a larger CIDR provides more IP addresses for Glue ENIs. Option A is wrong because increasing the number of retries does not fix the root cause. Option C is wrong because Glue does not have a connection timeout setting that would help; the issue is network connectivity, not job timeout. Option D is wrong because the existing security group already allows inbound traffic on port 5432; adding an inbound rule for ephemeral ports is unnecessary for PostgreSQL connections.

Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

✗
Set the Glue job timeout to 60 minutes to ensure the job does not fail prematurely.
Why it's wrong here
The error indicates a connection timeout, not a job timeout; increasing job timeout does not fix network connectivity.
✓
Change the subnet of the Glue job to one with a larger CIDR range (e.g., /20 instead of /24).
Why this is correct
A larger subnet provides more available IP addresses, reducing the chance of exhausting the pool for Glue ENIs.
Clue confirmation
The clue word "immediately / without restart" in the question point toward this answer.
Related concept
CIDR notation defines the prefix length.
✗
Add an inbound rule to the RDS security group allowing traffic on ports 1024-65535 from the Glue security group.
Why it's wrong here
PostgreSQL uses port 5432; ephemeral ports are not required for this connection.
✗
Increase the number of retries in the Glue job configuration to 5.
Why it's wrong here
Retries do not address the root cause of network connectivity failures.

Common exam traps

Common exam trap: usable hosts are not the same as total addresses

Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.

Detailed technical explanation

How to think about this question

Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.

KKey Concepts to Remember

CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.

TExam Day Tips

Write the block size before choosing the subnet.
Check whether the question asks for hosts, subnets or a specific address range.
Do not confuse /24, /25, /26 and /27 host counts.

Key takeaway

Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.

Real-world example

How this comes up in practice

A media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.

What to study next

Got this wrong? Here's your next step.

Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related DEA-C01 subnetting questions on CIDR, address ranges, and subnet selection.

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FAQ

Questions learners often ask

What does this DEA-C01 question test?

Data Operations and Support — This question tests Data Operations and Support — CIDR notation defines the prefix length..

What is the correct answer to this question?

The correct answer is: Change the subnet of the Glue job to one with a larger CIDR range (e.g., /20 instead of /24). — Option B is correct because the timeout suggests network connectivity issues, likely due to Glue's dynamic IP allocation exhausting available IP addresses in the subnet's CIDR range, which causes connection failures when no IP is available. Resizing the subnet to a larger CIDR provides more IP addresses for Glue ENIs. Option A is wrong because increasing the number of retries does not fix the root cause. Option C is wrong because Glue does not have a connection timeout setting that would help; the issue is network connectivity, not job timeout. Option D is wrong because the existing security group already allows inbound traffic on port 5432; adding an inbound rule for ephemeral ports is unnecessary for PostgreSQL connections.

What should I do if I get this DEA-C01 question wrong?

Are there clue words in this question I should notice?

Yes — watch for: "immediately / without restart". Time or reboot constraint — the correct answer must take effect right away without requiring a reboot or reload.

What is the key concept behind this question?

CIDR notation defines the prefix length.

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