Log Levels Explained: DEBUG, INFO, WARN, ERROR & Best Practices

Log levels classify messages by urgency, enabling teams to filter, route, query, and alert on operational signals without overwhelming engineers with noise. The standard hierarchy ranges from TRACE and DEBUG for fine-grained diagnostic details, through INFO for normal system activity and WARN for recoverable or abnormal conditions, to ERROR for genuine failures and FATAL or CRITICAL for failures that prevent continued operation. Effective use depends on shared definitions across services, environment-specific thresholds, runtime configurability, structured fields, sufficient contextual identifiers, and strict avoidance of sensitive data at every level. The discussion notes that implementations vary among Python, Java, Node.js, and syslog, particularly in naming and numeric severity order, making careful configuration important in multi-language systems. It also emphasizes reserving ERROR alerts for actionable failures, monitoring sustained WARN increases, and sampling high-volume DEBUG or TRACE events to control costs and reduce alert fatigue, with OpenObserve presented as a platform for structured severity-based querying, retention, and alerting.

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