Logs, metrics, traces. ELK stack, Loki, OpenTelemetry. Pilar observability modern.
Logs (event detail). Metrics (numeric over time). Traces (request flow across service). Saling melengkapi. Modern app butuh ketiga, tidak hanya 1.
Structured logs (JSON, bukan plain text). Centralize ke log server. Log level appropriate (DEBUG, INFO, WARN, ERROR). Tidak log sensitive data (password, PII). Retention policy.
Elasticsearch (storage dan search). Logstash (ingest dan transform). Kibana (visualisasi). Stack klasik tapi heavy. Modern alternative: Grafana Loki yang lebih ringan.
Jejak request lewat banyak microservice. OpenTelemetry standar terbuka. Tools: Jaeger, Zipkin, Tempo. Bantu debug latency issue di sistem kompleks.
Logs bisa mahal (terabytes per hari). Strategy: filter spam log, sampling untuk traces, retention policy ketat. Pakai cheap storage untuk archive. Hot vs cold tier.