Step 01 of 06
Learn the concept
Logs are what you have before the dashboard catches up. Free-form prose feels nice until you need every request with target=example.com and status=500. Structured logs make the computer do the searching.
The ideas this is made of
Attributes beat string parsing
logger.Info("check complete", "target", target, "latencyMs", 82) records fields separately from the message. A log system can filter latencyMs > 1000 without regex. Humans still get a sentence. Machines get columns. Everyone is less annoyed.
Levels are a budget
Debug is for development detail, info for normal lifecycle events, warn for degraded but handled conditions, and error for failed operations that need attention. If every slow check is error, real errors drown. If storage failure is info, no one sees it. Levels are not decoration.
Correlation IDs join the path
A request ID generated at the HTTP edge should appear in every log produced while handling that request. It lets an operator follow one failing call across middleware, handler and store. Use a header if supplied by trusted infrastructure; otherwise generate one.
Some data must never enter logs
Secrets, bearer tokens, cookies, private keys and personal data do not belong in logs. Logs spread: terminals, files, collectors, tickets, screenshots. Beacon does not use credentials in this course, but the habit matters before course five introduces cloud identity.
package main
import (
"log/slog"
"os"
)
func main() {
logger := slog.New(slog.NewJSONHandler(os.Stdout, nil))
logger.Info("check complete", "target", "https://example.com", "latencyMs", 82)
}The output is one JSON object with stable keys. Beacon will add request IDs and route names the same way.
Text or JSON handler
| Handler | Good for | Trade-off |
|---|---|---|
Text | Local reading | Harder to query |
JSON | Collectors | Noisier by eye |
Both | Same call sites | Configured at startup |
What these are called on the job
Attribute — A key-value pair attached to a log record.
Correlation ID — An identifier repeated across logs for one request or unit of work.
PII — Personally identifiable information, which should not be casually logged.