- A
chain: "{{ item.dport | regex_replace('^(80|443)$', 'INPUT') | default('FORWARD', true) }}"
Why wrong: regex_replace returns the original port string if not matched; default will not replace it because the result is not false.
- B
chain: "{{ (item.dport in [80,443]) | ternary('INPUT', 'FORWARD') }}"
Ternary correctly returns 'INPUT' for ports in the list, else 'FORWARD'.
- C
chain: "{{ item.dport | select('in', [80,443]) | list | first | default('FORWARD') }}"
Why wrong: select expects an iterable input; a single integer is not iterable, causing an error.
- D
chain: "{{ item.dport | replace('80','INPUT') | replace('443','INPUT') | default('FORWARD') }}"
Why wrong: replace filters mangle port numbers like 8080 into 'INPUT80' and do not return 'FORWARD' for unmatched ports.
EX294 Transform data with filters and plugins Practice Question
This EX294 practice question tests your understanding of transform data with filters and plugins. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 automation is used to manage firewall rules on a set of Linux servers. The playbook defines a variable "allow_rules" as: allow_rules: - proto: tcp dport: 80 comment: HTTP - proto: tcp dport: 443 comment: HTTPS
The engineer needs to use the "iptables" module to create rules. The module expects "chain" to be specified, and the engineer wants to dynamically set the chain based on the port: ports 80 and 443 go to "INPUT" chain, while others go to "FORWARD". The engineer writes a loop: - name: Add iptables rules iptables: chain: "{{ item.dport | map('some_filter') }}" protocol: "{{ item.proto }}" destination_port: "{{ item.dport }}" comment: "{{ item.comment }}" loop: "{{ allow_rules }}"
But this fails because the chain field expects a string, not a list. The engineer realizes the map filter returns a list. Which of the following modifications correctly sets the chain based on port number?
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
chain: "{{ (item.dport in [80,443]) | ternary('INPUT', 'FORWARD') }}"
Option B is correct because it uses the `ternary` filter to evaluate a condition (`item.dport in [80,443]`) and return 'INPUT' if true, or 'FORWARD' if false. This produces a single string, which is exactly what the `chain` parameter expects, avoiding the list output from `map`.
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.
- ✗
chain: "{{ item.dport | regex_replace('^(80|443)$', 'INPUT') | default('FORWARD', true) }}"
Why it's wrong here
regex_replace returns the original port string if not matched; default will not replace it because the result is not false.
- ✓
chain: "{{ (item.dport in [80,443]) | ternary('INPUT', 'FORWARD') }}"
Why this is correct
Ternary correctly returns 'INPUT' for ports in the list, else 'FORWARD'.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
chain: "{{ item.dport | select('in', [80,443]) | list | first | default('FORWARD') }}"
Why it's wrong here
select expects an iterable input; a single integer is not iterable, causing an error.
- ✗
chain: "{{ item.dport | replace('80','INPUT') | replace('443','INPUT') | default('FORWARD') }}"
Why it's wrong here
replace filters mangle port numbers like 8080 into 'INPUT80' and do not return 'FORWARD' for unmatched ports.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often reach for `map` or `select` filters without realizing they produce lists, and then try to coerce them into strings with `first` or `join`, which can fail or produce unexpected results when the list is empty or contains non-string values.
Detailed technical explanation
How to think about this question
The `ternary` filter is a Jinja2 filter that acts like an inline if-else; it evaluates a condition and returns one of two values. In Ansible, this is often used to dynamically set parameters based on variable values. The `iptables` module expects `chain` to be a string like 'INPUT', 'FORWARD', or 'OUTPUT', and using `ternary` ensures a single string is returned, avoiding the common pitfall of accidentally generating a list.
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.
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FAQ
Questions learners often ask
What does this EX294 question test?
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: chain: "{{ (item.dport in [80,443]) | ternary('INPUT', 'FORWARD') }}" — Option B is correct because it uses the `ternary` filter to evaluate a condition (`item.dport in [80,443]`) and return 'INPUT' if true, or 'FORWARD' if false. This produces a single string, which is exactly what the `chain` parameter expects, avoiding the list output from `map`.
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
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Last reviewed: Jun 25, 2026
This EX294 practice question is part of Courseiva's free Red Hat certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the EX294 exam.
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