Question 75 of 528

Coordinate rolling updates →mediumMultiple SelectObjective-mapped

Ansible Rolling Update Best Practices with HAProxy

This EX294 practice question tests your understanding of coordinate rolling updates. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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 company uses Ansible to perform a rolling update of 10 web servers behind an HAProxy load balancer. The playbook uses the `serial` keyword and includes tasks to disable a host from the load balancer, update the web server package, and re-enable the host. Which TWO best practices should the administrator apply to minimize downtime and ensure a successful rolling update?

Clue words in this question

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

Clue: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Clue: "minimum / minimize"
Why it matters: Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.

A
Use `any_errors_fatal: true` to stop the playbook if any host fails.
Why wrong: This would halt the entire update on the first failure, which is not desirable for a rolling update where individual host failures are acceptable.
B
Set `serial: 1` to update one host at a time.
Updating one host at a time minimizes the impact on the load balancer pool and ensures continuous service availability.
C
Use `throttle: 1` to limit the number of concurrent tasks across all hosts.
Why wrong: Throttle limits task concurrency but does not control the batch size within a rolling update; it is not a substitute for serial.
D
Ensure the load balancer draining timeout is longer than the maximum expected update time per host.
This prevents the host from being re-enabled while the update is still in progress, avoiding serving traffic with an incomplete update.
E
Use `async` and `poll` to run the update tasks in the background while proceeding to the next host immediately.
Why wrong: Async is not appropriate because the update must complete before the host is re-enabled; background execution could lead to premature re-enablement.

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

✓

Set `serial: 1` to update one host at a time.

Option B is correct because setting `serial: 1` ensures that only one host is updated at a time, which is the safest way to perform a rolling update without overwhelming the load balancer or causing a service outage. This allows the playbook to complete the full update cycle (disable, update, re-enable) for each host before moving to the next, minimizing the number of hosts out of service simultaneously.

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.

✗
Use `any_errors_fatal: true` to stop the playbook if any host fails.
Why it's wrong here
This would halt the entire update on the first failure, which is not desirable for a rolling update where individual host failures are acceptable.
✓
Set `serial: 1` to update one host at a time.
Why this is correct
Updating one host at a time minimizes the impact on the load balancer pool and ensures continuous service availability.
Clue confirmation
The clue words "best", "minimum / minimize" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Use `throttle: 1` to limit the number of concurrent tasks across all hosts.
Why it's wrong here
Throttle limits task concurrency but does not control the batch size within a rolling update; it is not a substitute for serial.
✓
Ensure the load balancer draining timeout is longer than the maximum expected update time per host.
Why this is correct
This prevents the host from being re-enabled while the update is still in progress, avoiding serving traffic with an incomplete update.
Clue confirmation
The clue words "best", "minimum / minimize" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Use `async` and `poll` to run the update tasks in the background while proceeding to the next host immediately.
Why it's wrong here
Async is not appropriate because the update must complete before the host is re-enabled; background execution could lead to premature re-enablement.

Common exam traps

Common exam trap: answer the scenario, not the keyword

The trap here is confusing `serial` with `throttle` or `async`; candidates often think `throttle` or `async` can achieve the same serialization, but only `serial` ensures one host completes the entire update cycle before the next begins, which is essential for minimizing downtime in a rolling update scenario.

Detailed technical explanation

How to think about this question

The `serial` keyword in Ansible controls the number of hosts that are processed in each batch, effectively creating a mini-playbook run per batch. When `serial: 1` is used, Ansible runs the entire playbook on one host, including all tasks, before moving to the next. This is critical for rolling updates behind HAProxy because the load balancer's draining timeout must be set longer than the maximum expected update time per host; otherwise, HAProxy may forcibly close connections to a host that is still being updated, causing dropped traffic. The `throttle` keyword, by contrast, limits task concurrency but does not serialize host processing, so multiple hosts can be in different task phases simultaneously.

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 practitioner preparing for the EX294 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.

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.

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FAQ

Questions learners often ask

What does this EX294 question test?

Coordinate rolling updates — This question tests Coordinate rolling updates — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: Set `serial: 1` to update one host at a time. — Option B is correct because setting `serial: 1` ensures that only one host is updated at a time, which is the safest way to perform a rolling update without overwhelming the load balancer or causing a service outage. This allows the playbook to complete the full update cycle (disable, update, re-enable) for each host before moving to the next, minimizing the number of hosts out of service simultaneously.

What should I do if I get this EX294 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: "best", "minimum / minimize". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.

What is the key concept behind this question?

Read the scenario before looking for a memorised answer.

About these practice questions

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Same concept, more angles

1 more ways this is tested on EX294

These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.

Variation 1. An Ansible Engineer is planning a rolling update for a web application deployed across 10 nodes. The playbook uses the 'delegate_to' directive to manage load balancer health checks. Which of the following best describes the recommended approach to minimize downtime?

medium

✓ A.Use 'serial: 1' and delegate load balancer disable/enable tasks to localhost, ensuring each node is taken out of rotation before updating.
B.Run the update playbook with 'serial: 10' to update all nodes at once, then run a separate playbook to update the load balancer.
C.Run the update on each node manually using 'ansible-playbook --limit' and skip load balancer management to save time.
D.Use 'strategy: free' to allow nodes to update independently without controlling the load balancer.

Why A: Option A is correct because using 'serial: 1' ensures that only one node is updated at a time, and delegating load balancer disable/enable tasks to localhost (or the Ansible control node) allows the playbook to interact with the load balancer API to remove the node from the pool before the update and re-add it after. This minimizes downtime by ensuring traffic is not sent to a node being updated, while other nodes continue serving requests.

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