Top 50 Prometheus Interview Question and Answers

17 Oct 2024 - Shyam Mohan

1. What is Prometheus, and why is it used?
   • Prometheus is an open-source monitoring and alerting toolkit designed primarily for reliability and scalability. It’s used for monitoring systems and services, gathering metrics, and generating alerts.
2. What is the difference between Prometheus and Grafana?
   • Prometheus focuses on collecting and storing time-series data, while Grafana is a visualization tool that can display and analyze data from Prometheus and other sources.
3. Explain the Prometheus architecture.
   • Prometheus consists of a server, data storage, a time-series database, exporters, and Alertmanager. The server scrapes metrics from endpoints, stores them, and generates alerts based on rule evaluations.
4. What is a Prometheus scrape target?
   • A scrape target is an endpoint (URL) from which Prometheus collects metrics data. This can be an application, a database, or any service exposing metrics.
5. What are Prometheus exporters?
   • Exporters are lightweight applications or integrations that collect metrics from specific services (e.g., MySQL, Redis) and expose them in a format Prometheus can scrape.
6. What are labels in Prometheus?
   • Labels are key-value pairs attached to each time-series metric, helping to differentiate metrics with the same name from different sources.
7. What is a metric in Prometheus?
   • A metric in Prometheus is a set of time-series data identified by a name and optional key-value labels that describe different attributes of the metric.
8. List the metric types supported by Prometheus.
   • Counter, Gauge, Histogram, and Summary.
9. Explain the difference between a Counter and a Gauge.
   • A Counter is a cumulative metric that only increases or resets to zero, while a Gauge can increase or decrease, representing a current value.
10. What is PromQL, and why is it important?
    • PromQL is Prometheus’s query language, allowing users to query and aggregate time-series data, perform math operations, and analyze metrics.
11. What is the use of the rate() function in PromQL?
    • rate() calculates the per-second average increase of a counter over a specified range. It’s often used to analyze data over time.
12. How does the sum aggregation work in Prometheus?
    • sum aggregates values across multiple time series and can be used to compute totals for metrics across different labels.
13. What is a subquery in Prometheus?
    • Subqueries allow you to apply an operation on the results of another query, helpful for calculating and visualizing complex metrics.
14. What is a recording rule in Prometheus?
    • A recording rule allows users to precompute frequently needed or expensive queries and store the results for later use.
15. What is the Prometheus configuration file, and what is its role?
    • Prometheus’s configuration file (prometheus.yml) defines scrape jobs, rules, alerting configurations, and other essential settings.
16. Explain scrape_interval and scrape_timeout in Prometheus.
    • scrape_interval is how often Prometheus collects data from targets, and scrape_timeout is the maximum time Prometheus will wait for a target to respond.
17. What is the role of Alertmanager in Prometheus?
    • Alertmanager handles alerts generated by Prometheus, managing deduplication, grouping, and routing notifications to various channels like email, Slack, and PagerDuty.
18. What are Service Discovery mechanisms in Prometheus?
    • Service discovery mechanisms help Prometheus dynamically discover targets from services like Kubernetes, Consul, and EC2 instances.
19. How do you enable authentication in Prometheus?
    • Prometheus itself lacks native authentication, but reverse proxies like Nginx or Grafana can provide secure access with authentication.
20. What are relabeling rules in Prometheus?
    • Relabeling rules help modify and control which targets Prometheus scrapes by adjusting labels or filtering based on conditions.
21. What is a federation in Prometheus?
    • Federation is used to aggregate metrics from multiple Prometheus instances into a central instance.
22. Explain the term “sharding” in the context of Prometheus.
    • Sharding distributes scrape targets across multiple Prometheus instances to handle high cardinality and improve scalability.
23. What is Prometheus Pushgateway, and when is it used?
    • Pushgateway allows ephemeral or short-lived jobs to push metrics to Prometheus, useful for jobs that cannot be continuously scraped.
24. How does Prometheus handle high-cardinality data?
    • Prometheus handles high-cardinality data by using a time-series database but can experience issues if labels are too dynamic or metrics grow uncontrollably.
25. What are Thanos and Cortex in relation to Prometheus?
    • Thanos and Cortex are extensions that allow for long-term storage, global query capabilities, and horizontal scalability with Prometheus.
26. How can Prometheus integrate with Kubernetes?
    • Prometheus can automatically discover and scrape Kubernetes metrics through the Kubernetes Service Discovery API.
27. What is the use of Grafana with Prometheus?
    • Grafana is used to visualize Prometheus data, creating rich dashboards and helping teams monitor and analyze metrics effectively.
28. How can you reduce Prometheus storage usage?
    • Optimize retention period, lower the scrape interval, avoid high-cardinality metrics, and use recording rules to reduce query complexity.
29. How to troubleshoot high memory usage in Prometheus?
    • Identify high-cardinality metrics, optimize the configuration, and consider external storage solutions like Thanos or Cortex.
30. What are some best practices for designing Prometheus alerts?
    • Use meaningful thresholds, reduce noise by aggregating alerts, apply deduplication, and tune alert timing to avoid flapping.
31. How can Prometheus be made highly available?
    • Use multiple instances with external storage backends (e.g., Thanos or Cortex) for redundancy, or use federation.
32. How to monitor Prometheus itself?
    • Prometheus exposes its own metrics at /metrics endpoint, and you can use Grafana to visualize health, query load, and other internal metrics.

Security and Scaling

1. How do you secure Prometheus endpoints?
   • Use reverse proxies for authentication, HTTPS, IP whitelisting, and firewalls to secure endpoints.
2. What is remote write in Prometheus?
   • Remote write allows Prometheus to push metrics to external storage systems for long-term storage.
3. How can Prometheus scale horizontally?
   • By using techniques like federation, sharding, and integrating with systems like Thanos for long-term scalability.
4. Explain the concept of retention period in Prometheus.
   • Retention period defines how long Prometheus stores metrics before deleting them, controlled by the --storage.tsdb.retention.time flag.
5. How does Prometheus handle timestamps?
   • Prometheus uses UNIX timestamps in seconds and milliseconds for each metric data point.
6. What is the default port for Prometheus?
   • The default HTTP server port for Prometheus is 9090.
7. What is Prometheus Operator?
   • The Prometheus Operator simplifies managing Prometheus instances in Kubernetes, providing CRDs to configure Prometheus, Alertmanager, and related components.
8. What is node_exporter in Prometheus?
   • node_exporter is a widely used exporter for collecting host-level metrics, such as CPU, memory, disk, and network statistics.
9. Can Prometheus monitor Windows servers?
   • Yes, with windows_exporter, Prometheus can collect metrics from Windows servers.
10. How to delete specific metrics in Prometheus?
    • Metrics cannot be selectively deleted in Prometheus; retention policies control data deletion.
11. What is the Prometheus API used for?
    • Prometheus API allows querying metrics, accessing metadata, and managing alerts.
12. How does Prometheus handle downtime?
    • Prometheus lacks built-in clustering, so downtime means no metrics collection. Solutions like Thanos can provide failover support.
13. What are Prometheus’s limitations?
    • Prometheus lacks built-in HA support, limited long-term storage, and can have issues with high-cardinality data.
14. What is Alertmanager’s “silence” feature?
    • The “silence” feature temporarily suppresses alerts based on specified matchers (e.g., labels).
15. How do you monitor microservices with Prometheus?
    • Use service-specific exporters and labels to track performance across individual services within a microservices architecture.
16. What are good practices for naming metrics in Prometheus?
    • Use clear, descriptive names and suffixes like _total, _count, or _bytes to define metrics accurately.
17. What does up metric represent in Prometheus?
    • The up metric checks if a target is reachable (1 if up, 0 if down).
18. How do you monitor Prometheus’s own health?
    • Use its built-in metrics and create alerts on CPU, memory usage, and scrape performance metrics.