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.
Which TWO of the following are valid 'serial' values for an Ansible rolling update playbook?
serial: [1,2,3]
Why wrong: While serial can be a list in some versions, it is not a standard rolling update pattern and may not be supported in all environments.
serial: 50%
A percentage is a valid value.
serial: 1
Specifies exactly one host per batch.
serial: '25%'
Why wrong: Percentages must be integers without quotes (e.g., serial: 25%).
serial: 'batch'
Why wrong: Serial does not accept string names.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
serial: 50%
Option B is correct because Ansible's 'serial' keyword accepts a percentage value to control how many hosts are updated at a time during a rolling update. The format '50%' (without quotes in YAML) tells Ansible to update half of the hosts in the batch, which is a valid and commonly used pattern for gradual rollouts.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
serial: [1,2,3]
Why it's wrong here
While serial can be a list in some versions, it is not a standard rolling update pattern and may not be supported in all environments.
serial: 50%
Why this is correct
A percentage is a valid value.
Related concept
Read the scenario before looking for a memorised answer.
serial: 1
Why this is correct
Specifies exactly one host per batch.
Related concept
Read the scenario before looking for a memorised answer.
serial: '25%'
Why it's wrong here
Percentages must be integers without quotes (e.g., serial: 25%).
serial: 'batch'
Why it's wrong here
Serial does not accept string names.
Common exam traps
The trap here is that candidates confuse the valid 'serial' syntax with other Ansible constructs like 'batch' or lists, or incorrectly assume that quoted percentage strings are acceptable, when in fact Ansible requires the percentage as a bare value without quotes.
Detailed technical explanation
Under the hood, the 'serial' directive controls the 'batch size' for the 'strategy: linear' (default) or 'strategy: free' play execution. When set to a percentage, Ansible calculates the number of hosts as 'ceil(percentage/100 * total_hosts)', ensuring at least one host is updated even with a small percentage. This is critical for zero-downtime deployments where you want to limit the blast radius of a failed update.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
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FAQ
Coordinate rolling updates — This question tests Coordinate rolling updates — Read the scenario before looking for a memorised answer..
The correct answer is: serial: 50% — Option B is correct because Ansible's 'serial' keyword accepts a percentage value to control how many hosts are updated at a time during a rolling update. The format '50%' (without quotes in YAML) tells Ansible to update half of the hosts in the batch, which is a valid and commonly used pattern for gradual rollouts.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 25, 2026
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