PCA Promql Practice Question
You need to perform a binary operation between two vectors where the left vector has labels {job="api", instance="a"} and the right vector has labels {job="api"}. You want to match them using the job label while retaining the instance label from the left side. Which modifier configuration is correct?
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
✓
vector_a * on(job) group_left(instance) vector_b
To match on a subset of labels while retaining extra labels on the left side during a one-to-many or many-to-one operation, group_left must be used with the on modifier.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
vector_a * on(instance) group_left(job) vector_b
Why it's wrong here
Matching on instance would fail because instance is not present on the right vector.
- ✗
vector_a * on(job) group_right(instance) vector_b
Why it's wrong here
group_right pulls labels from the right side, but instance is on the left side.
- ✓
vector_a * on(job) group_left(instance) vector_b
Why this is correct
Correct. on(job) matches on job, and group_left(instance) pulls the instance label from the left side.
- ✗
vector_a * ignoring(instance) group_left vector_b
Why it's wrong here
ignoring instance would fail if instance is only present on the left side without proper grouping syntax.
About these practice questions
This PCA question is part of Courseiva's 304-question bank — original exam-style content with full explanations and wrong-answer analysis, never real exam questions or exam dumps. Learn why practice questions differ from exam dumps →
JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed August 2026 · checked against the official CNCF / Linux Foundation exam blueprint
This PCA practice question is part of Courseiva's free CNCF / Linux Foundation 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 PCA exam.