44 lines
1.7 KiB
Go
44 lines
1.7 KiB
Go
// Package logging builds the single *slog.Logger instance shared across the
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// whole application. Every log line the app writes goes through this
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// logger, formatted as JSON to stdout.
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//
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// Why JSON to stdout specifically? This is the standard "12-factor app"
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// approach to logging: the application doesn't know or care where its logs
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// end up (a file, Loki, Elasticsearch, ...) - it just writes structured
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// lines to stdout, and an external agent (in your case, Grafana Alloy)
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// takes care of collecting, parsing, and shipping them. Because every line
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// is valid JSON with consistent keys, Alloy/Loki can index and query on
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// fields like "status", "path", or "request_id" without any custom parsing
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// rules or regexes.
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package logging
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import (
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"log/slog"
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"os"
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)
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// New builds and returns the application's structured logger.
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//
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// The minimum log level is controlled by the LOG_LEVEL environment
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// variable: set LOG_LEVEL=debug to see verbose Debug()-level output;
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// anything else (or unset) defaults to Info level, which hides Debug logs.
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func New() *slog.Logger {
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level := slog.LevelInfo
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if os.Getenv("LOG_LEVEL") == "debug" {
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level = slog.LevelDebug
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}
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// slog.NewJSONHandler formats every log record as a single-line JSON
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// object and writes it to the given io.Writer (here, os.Stdout).
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// Swapping this for slog.NewTextHandler would switch to human-readable
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// text output instead - useful for local dev if you ever want it - but
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// every other part of the app that calls logger.Info/Error/etc would
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// stay completely unchanged, since they only depend on *slog.Logger,
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// not on which Handler is behind it.
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handler := slog.NewJSONHandler(os.Stdout, &slog.HandlerOptions{
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Level: level,
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})
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return slog.New(handler)
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}
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