#logging

Build centralized logging with ELK stack (Elasticsearch, Logstash, Kibana). Pipeline: 1. Filebeat agents on application servers. 2. Logstash for log parsing and enrichment. 3. Elasticsearch cluster for storage and indexing. 4. Kibana for visualization and search. 5. Index lifecycle management for retention. 6. Alerting on error patterns. 7. Log correlation across services. Use structured logging (JSON). Include security (authentication, encryption) and performance tuning (sharding, replicas).

Handle errors and log effectively. Practices: 1. Catch errors at boundaries. 2. Specific error types vs generic. 3. User-friendly error messages. 4. Detailed logs for debugging. 5. Structured logging (JSON). 6. Log levels (ERROR, WARN, INFO, DEBUG). 7. Correlation IDs for tracing. 8. Never log sensitive data. Use Winston, Pino, or similar. Centralize logs with ELK or Datadog. Monitor error rates.