Site Reliability Engineering interview question · Most asked
What are the four golden signals?
Summary
Latency, traffic, errors and saturation. If you can only measure four things about a user-facing system, measure these.
Longer Answer
- Latency: time to serve requests; track successful and failed requests separately (fast errors can make latency look good) and use percentiles.
- Traffic: demand, such as requests per second or concurrent sessions.
- Errors: rate of failed requests, explicit (5xx) and implicit (wrong content, too slow per policy).
- Saturation: how full the most constrained resource is (CPU, memory, I/O, queue depth, connection pools), ideally predictive ("disk full in 4 hours").
They complement SLIs: SLOs say whether users are happy; golden signals help explain why not.
Key Points
- Latency, traffic, errors, saturation.
- Separate latency of errors.
- Saturation of the constrained resource.
- Pair with SLOs.
Deep dive: Observability and Operations
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