Datadog

Agent-based SaaS for metrics, APM/tracing, log management, and SLO-driven alerting

Datadog is an agent-based SaaS platform: a single agent per host ships metrics, traces and logs to Datadog's backend, where they are correlated by tags. Interviews on Datadog rarely test the UI. They test whether you understand the cost and cardinality model — that custom metrics are billed per unique tag combination, and that an unbounded tag such as a user ID or request ID will multiply your bill and slow your queries. Expect questions on how the APM tracer propagates context across service boundaries, how trace sampling decisions are made at the head versus the tail, and how monitors, SLOs and error budgets fit together. A strong answer connects the three signals: a monitor fires on a metric, you pivot to the trace that explains it, and you read the logs attached to that trace. A weaker answer describes each signal in isolation.