What should you measure first for a service? Explain the golden signals (or RED/USE).
What they are really testing: Whether you have a principled starting set (latency, traffic, errors, saturation) rather than measuring everything randomly. Knowing RED vs USE shows depth.
A real interview question
What should you measure first for a service? Explain the golden signals (or RED/USE).
What most people say
drag me
“I would measure CPU, memory, and disk usage of the servers.”
Those are resource metrics (part of USE) but not what users feel. The golden signals start with latency and errors of user requests; leading with CPU misses the symptoms that actually matter.
The follow-ups they ask next
What is the difference between RED and USE?
RED (Rate, Errors, Duration) is for request-driven services, the user-facing view. USE (Utilization, Saturation, Errors) is for resources like CPU/memory/disk. Use RED for services, USE for the resources behind them.
Why measure latency and errors before CPU?
Latency and errors are symptoms users feel and what SLOs are built on; CPU is a cause you investigate after a symptom appears. High CPU with healthy latency may not matter; high latency always does.
What the interviewer is listening for
- Names the four golden signals
- Knows RED for services, USE for resources
- Starts with user-facing symptoms
What sinks the answer
- Leads with CPU/memory only
- No principled starting set
- Confuses resource metrics with user signals
If you genuinely do not know
Say this instead of freezing. Reasoning out loud from what you do know beats silence every single time, and a good interviewer is listening for exactly that.
“Start with [the four golden signals: latency, traffic, errors, saturation]. Use [RED (Rate, Errors, Duration) for request services] and [USE (Utilization, Saturation, Errors) for resources]. Measure [user-facing latency and errors first, they map to experience and SLOs], then [resource saturation to explain them]. CPU is [a cause to investigate, not the first symptom].”
Keep going with observability
Foundation
What is the difference between monitoring and observability?
Foundation
What are the three pillars of observability, and what is each good for?
Junior
What are good logging practices for a distributed system?
Junior
What are the main metric types (counter, gauge, histogram), and when do you use each?
Junior
What is distributed tracing, and how does it work?
Junior
How does Prometheus collect metrics, and what is the pull model?
Knowing the answer is not the same as recalling it under pressure
Sign in to send the questions you fumble to spaced recall, so they come back right before you would forget them, and learn the concepts behind them with hands-on labs.
Start free