PCA (Prometheus Certified Associate) sample exam question with answer 279

Question:
What is the purpose of the up time series in Prometheus?

1. To represent the total sum of all observed values for a metric
2. To count the number of events that have been observed for a metric
3. To provide cumulative counters for each observation bucket in a histogram
4. To indicate whether an instance is healthy and reachable

Answer:
D - correct answer. For each instance scrape, Prometheus stores a sample in the up time series with a value of 1 if the instance is healthy and reachable, or 0 if the scrape failed. This time series is useful for instance availability monitoring