Structured Logging and Log Levels
Adopt structured JSON logging and use log levels effectively so logs become queryable, machine-friendly signals.
Structured Logging and Log Levels is a free System Observability: Logging, Metrics & Tracing (ELK + OpenTelemetry) lesson on CoddyKit — lesson 4 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the System Observability: Logging, Metrics & Tracing (ELK + OpenTelemetry) learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
From Text to Structure
Plain text log lines are easy to write but hard for machines to query. Structured logging emits each entry as key-value data, usually JSON, that tools can index and filter precisely.
An Unstructured Line
Consider a typical free-text log. Extracting the user or order requires fragile regex parsing.
INFO User 42 placed order 1001 for $59.90The Structured Equivalent
The same event as JSON exposes each field explicitly, ready to query.
{"level":"INFO","event":"order_placed",
"userId":42,"orderId":1001,
"amount":59.90}Why Structure Wins
Structured logs let you ask precise questions, like all orders over $50 by user 42, without brittle text parsing. They power dashboards and alerts directly.
Log Levels Overview
Levels rank importance. Common levels from lowest to highest:
- DEBUG: detailed diagnostics
- INFO: normal events
- WARN: unexpected but recoverable
- ERROR: failures needing attention
Choosing the Right Level
Reserve ERROR for genuine failures and WARN for anomalies. Logging everything at ERROR makes real problems invisible in the noise.
Filtering by Level
Production usually runs at INFO and above, while development enables DEBUG. The level acts as a volume knob you can turn without code changes.
logger.setLevel(Level.INFO);Adding Context Fields
Attach contextual keys like a request ID to every log in a flow so you can correlate entries across a single operation.
{"event":"db_query",
"requestId":"abc-123",
"durationMs":42}Avoid Logging Secrets
Structured fields make it easy to accidentally log passwords or tokens. Redact sensitive values before emitting the entry.
Consistency Matters
Use consistent field names across services, e.g. always userId, never sometimes uid. Consistency makes cross-service queries possible.
Feeding the Pipeline
Structured logs flow cleanly into collectors and search systems like the ELK stack, where indexed fields enable fast filtering and visualization.
Quick Check
What is the main advantage of structured (JSON) logs over plain text?
Recap
You learned structured logging:
- Emit logs as key-value JSON, not free text
- Use levels (DEBUG/INFO/WARN/ERROR) as a volume knob
- Add correlating context like request IDs
- Keep field names consistent and redact secrets
Frequently asked questions
Is the “Structured Logging and Log Levels” lesson free?
Yes — the full text of “Structured Logging and Log Levels” is free to read here on the web, and the System Observability: Logging, Metrics & Tracing (ELK + OpenTelemetry) course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the System Observability: Logging, Metrics & Tracing (ELK + OpenTelemetry) course, upgrade to CoddyKit PRO.
What will I learn in “Structured Logging and Log Levels”?
Adopt structured JSON logging and use log levels effectively so logs become queryable, machine-friendly signals. You practise System Observability: Logging, Metrics & Tracing (ELK + OpenTelemetry) with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start System Observability: Logging, Metrics & Tracing (ELK + OpenTelemetry)?
No prior experience is required. System Observability: Logging, Metrics & Tracing (ELK + OpenTelemetry) on CoddyKit is structured for beginners through advanced learners; this is — lesson 4 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “Structured Logging and Log Levels” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this System Observability: Logging, Metrics & Tracing (ELK + OpenTelemetry) lesson?
Yes. Every System Observability: Logging, Metrics & Tracing (ELK + OpenTelemetry) lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- Understanding Modern Log Formats
- Centralized Logging Concepts
- Basic Log Collection and Parsing
- Structured Logging and Log Levels