Question 1

What are the three pillars of observability?

Accepted Answer

**Target Audience:** Beginners who have seen a dashboard or grepped a log file and want to understand what observability means, and candidates who need crisp vocabulary for an interview.
**Difficulty:** Medium
**Verified with:** Node 22.22 and Python 3.12 (both print identical output). The history of the "three pillars" phrase is from CrowdStrike's "Observability (Re)defined" article; the profiles signal status from the OpenTelemetry documentation and ClickHouse's write-up of the Alpha announcem

Question 2

How would you design OpenTelemetry tracing for 200 microservices?

Accepted Answer

**Target Audience:** Engineers who know what a trace is (see the pillars doc) and want to design tracing for a real, polyglot microservice fleet, and candidates preparing for an observability design round.
**Difficulty:** Medium
**Verified with:** Node 22.22 and Python 3.12 (both print identical output). Header format from the W3C Trace Context Recommendation; Collector component behaviour from the loadbalancing exporter README on pkg.go.dev and Grafana Alloy documentation of the tail sampling p

Question 3

Head vs tail sampling in OpenTelemetry — when does each break?

Accepted Answer

**Target Audience:** Engineers who have set up tracing and now have to choose a sampling strategy, and candidates who want to discuss sampling trade-offs with numbers rather than slogans.
**Difficulty:** Medium
**Verified with:** Node 22.22 and Python 3.12 (both print identical output). Tail sampling processor settings (`decision_wait` default 30 s described as time since the first span, `num_traces` default 50000) from the Grafana Alloy reference for `otelcol.processor.tail_sampling` (a wrapper

SYSTEM DESIGNDECODED.

Medium

What are the three pillars of observability?

How would you design OpenTelemetry tracing for 200 microservices?

Head vs tail sampling in OpenTelemetry — when does each break?