EX294 Coordinate rolling updates Practice Question
You are writing an Ansible playbook to perform a rolling update of a 20-node RHEL application cluster. The application requires that no more than 20 percent of the fleet be offline at any time. You want the playbook to update hosts in batches that respect this constraint and to abort the entire rollout if the failure rate within any batch exceeds 10 percent. Which combination of play keywords should you use?
⚠ Common exam trap
Candidates often confuse percentage-based serial values with absolute host counts, or assuming max_fail_percentage applies to the whole inventory rather than only to the hosts in the current serial batch.
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: 20%` and `max_fail_percentage: 10`
The requirement is to cap concurrent offline hosts at 20 percent of the fleet while aborting when batch failures exceed 10 percent. With 20 nodes, 20 percent equals 4 hosts, so `serial: 20%` expresses the constraint as a percentage that scales with inventory size. `max_fail_percentage: 10` then aborts the play when more than 10 percent of the hosts in the current batch fail. Together they encode both the availability and failure-tolerance policies directly in the play.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
`serial: 4` and `max_fail_percentage: 25`
Why it's wrong here
A serial of 4 correctly limits each batch to 20 percent of the fleet, but max_fail_percentage of 25 allows one failure in a 4-host batch (25 percent) before aborting, which does not match the required 10 percent failure threshold. The abort condition is too permissive for the stated policy.
- ✗
`serial: 4` and `max_fail_percentage: 10`
Why it's wrong here
A serial of 4 gives 5 percent of the 20-node fleet per batch, which is well under the 20 percent cap, but the scenario asks for batches sized to the constraint. More importantly, max_fail_percentage is calculated against the number of hosts in the current batch, so with only 4 hosts a single failure is 25 percent, exceeding 10 percent and aborting immediately. This configuration is overly strict in practice.
- ✓
`serial: 20%` and `max_fail_percentage: 10`
Why this is correct
Using `serial: 20%` sizes each batch to 20 percent of the 20-node fleet, which is exactly 4 hosts, satisfying the requirement that no more than 20 percent be offline. `max_fail_percentage: 10` then aborts the rollout if more than 10 percent of the hosts in the current batch fail. This directly encodes both constraints in the play.
- ✗
`serial: 20` and `max_fail_percentage: 10`
Why it's wrong here
`serial: 20` means all 20 hosts are updated in a single batch, taking the entire fleet offline at once and violating the 20 percent availability constraint. The max_fail_percentage value is irrelevant because the batch size itself breaks the requirement. This would cause a full outage rather than a rolling update.
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Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Red Hat exam blueprint
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