- A
forks: 2
Why wrong: Incorrect: forks controls the number of parallel tasks across all hosts, not batching per play.
- B
max_fail_percentage: 2
Why wrong: Incorrect: This sets the percentage of hosts that can fail before aborting, not concurrency control.
- C
throttle: 2
Why wrong: Incorrect: throttle limits the number of concurrent executions per task, but does not batch hosts at the play level.
- D
serial: 2
Correct: 'serial: 2' ensures that tasks run on at most 2 hosts at a time, providing controlled rolling updates.
Question 524 of 528
Ansible Serial Keyword for Rolling Updates — Controlling Concurrency | Red Hat Certified Engineer Explained
This EX294 practice question tests your understanding of implement advanced ansible automation. 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.
An Ansible playbook runs tasks on a group of web servers. During a rolling update, the playbook should ensure that no more than 2 servers are taken out of service at the same time. Which play keyword should be used?
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
✓
serial: 2
The `serial` keyword controls the batch size of hosts that Ansible executes a play against. Setting `serial: 2` ensures that only 2 web servers are processed at a time, which is exactly what is needed for a rolling update where no more than 2 servers should be taken 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.
- ✗
forks: 2
Why it's wrong here
Incorrect: forks controls the number of parallel tasks across all hosts, not batching per play.
- ✗
max_fail_percentage: 2
Why it's wrong here
Incorrect: This sets the percentage of hosts that can fail before aborting, not concurrency control.
- ✗
throttle: 2
Why it's wrong here
Incorrect: throttle limits the number of concurrent executions per task, but does not batch hosts at the play level.
- ✓
serial: 2
Why this is correct
Correct: 'serial: 2' ensures that tasks run on at most 2 hosts at a time, providing controlled rolling updates.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is confusing `serial` (which controls batch size of hosts) with `forks` (which controls parallelism of task execution), leading candidates to pick `forks: 2` thinking it limits concurrency, when in fact it only limits the number of parallel task processes, not the number of hosts taken out of service simultaneously.
Detailed technical explanation
How to think about this question
Under the hood, `serial` works by dividing the inventory into batches and executing the entire play (all tasks) on each batch sequentially before moving to the next. A subtle behavior is that if a batch fails, the playbook stops by default, but you can combine `serial` with `max_fail_percentage` to allow partial failures. In real-world rolling updates, this prevents service disruption by ensuring only a subset of servers are updated at once, while the rest continue serving traffic.
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?
Implement advanced Ansible automation — This question tests Implement advanced Ansible automation — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: serial: 2 — The `serial` keyword controls the batch size of hosts that Ansible executes a play against. Setting `serial: 2` ensures that only 2 web servers are processed at a time, which is exactly what is needed for a rolling update where no more than 2 servers should be taken 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.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
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 playbook uses a rolling update strategy with serial: 1. After the first host is updated, the playbook stops and shows 'PLAY RECAP' with only one host. What is the most likely reason?
hard- A.the playbook has a 'failed_when' condition that stops execution
- ✓ B.the inventory contains only one host
- C.the play uses 'delegate_to' incorrectly
- D.the playbook does not have any task that triggers the next batch, and 'serial' only controls concurrency, not retry
Why B: The `serial: 1` directive in Ansible limits concurrency to one host at a time, but the playbook will still process all hosts in the inventory. If the playbook stops after the first host and shows PLAY RECAP with only one host, the most likely reason is that the inventory contains only one host. With a single host, the play executes on that host and then finishes. Option B accurately identifies this scenario.
Keep practising
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Last reviewed: Jul 4, 2026
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