EX294 Transform data with filters and plugins Practice Question
This EX294 practice question tests your understanding of transform data with filters and plugins. 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 Tower and has defined a custom inventory script. The inventory returns JSON with nested groups. The playbook needs to list all hosts from a specific group 'webservers' that are not in the 'drain' subgroup. Which combination of filters correctly extracts these hosts?
Option D is correct because the `difference` filter in Ansible returns the elements of the first list that are not present in the second list. This directly matches the requirement: all hosts in the 'webservers' group that are not in the 'drain' subgroup.
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.
difference returns elements in first list not in second.
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 that candidates confuse `difference` with `symmetric_difference` (option A) or `intersect` (option B), often misreading the requirement as 'hosts not in drain' versus 'hosts in both groups'.
Detailed technical explanation
How to think about this question
The `difference` filter is implemented using Python's set difference operation, which is O(n) on average. In Ansible, `groups` is a dictionary of lists, so the filter works on list objects; however, if the inventory script returns nested groups, the `groups` variable already flattens inheritance, so `groups['webservers']` includes all hosts from child groups unless explicitly excluded. This filter is commonly used in dynamic inventories (e.g., AWS EC2, OpenStack) to exclude hosts under maintenance.
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 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.
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.
Transform data with filters and plugins — This question tests Transform data with filters and plugins — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: {{ groups['webservers'] | difference(groups['drain']) }} — Option D is correct because the `difference` filter in Ansible returns the elements of the first list that are not present in the second list. This directly matches the requirement: all hosts in the 'webservers' group that are not in the 'drain' subgroup.
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.
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Question Discussion
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