slog: Fluentd handler

A Fluentd Handler for slog Go library.

See also:

• slog-multi: slog.Handler chaining, fanout, routing, failover, load balancing...
• slog-formatter: slog attribute formatting
• slog-sampling: slog sampling policy

HTTP middlewares:

• slog-gin: Gin middleware for slog logger
• slog-echo: Echo middleware for slog logger
• slog-fiber: Fiber middleware for slog logger
• slog-chi: Chi middleware for slog logger
• slog-http: net/http middleware for slog logger

Loggers:

• slog-zap: A slog handler for Zap
• slog-zerolog: A slog handler for Zerolog
• slog-logrus: A slog handler for Logrus

Log sinks:

• slog-datadog: A slog handler for Datadog
• slog-betterstack: A slog handler for Betterstack
• slog-rollbar: A slog handler for Rollbar
• slog-loki: A slog handler for Loki
• slog-sentry: A slog handler for Sentry
• slog-syslog: A slog handler for Syslog
• slog-logstash: A slog handler for Logstash
• slog-fluentd: A slog handler for Fluentd
• slog-graylog: A slog handler for Graylog
• slog-quickwit: A slog handler for Quickwit
• slog-slack: A slog handler for Slack
• slog-telegram: A slog handler for Telegram
• slog-mattermost: A slog handler for Mattermost
• slog-microsoft-teams: A slog handler for Microsoft Teams
• slog-webhook: A slog handler for Webhook
• slog-kafka: A slog handler for Kafka
• slog-nats: A slog handler for NATS
• slog-parquet: A slog handler for Parquet + Object Storage
• slog-channel: A slog handler for Go channels

🚀 Install

go get github.com/samber/slog-fluentd/v2

Compatibility: go >= 1.21

No breaking changes will be made to exported APIs before v3.0.0.

💡 Usage

GoDoc: https://pkg.go.dev/github.com/samber/slog-fluentd/v2

Fluentd settings

<source>
    @type forward
    bind 0.0.0.0
    port 24224
</source>

Handler options

type Option struct {
    // log level (default: debug)
    Level slog.Leveler

    // connection to Fluentd
    Client *fluentd.Fluentd
    Tag    string

    // optional: customize json payload builder
    Converter Converter
    // optional: fetch attributes from context
    AttrFromContext []func(ctx context.Context) []slog.Attr

    // optional: see slog.HandlerOptions
    AddSource   bool
    ReplaceAttr func(groups []string, a slog.Attr) slog.Attr
}

Attributes will be injected in log payload.

Fluentd tag can be inserted in logger options or in a record attribute of type string.

Other global parameters:

slogfluentd.SourceKey = "source"
slogfluentd.ContextKey = "extra"
slogfluentd.ErrorKeys = []string{"error", "err"}

Example

import (
    "github.com/fluent/fluent-logger-golang/fluent"
    slogfluentd "github.com/samber/slog-fluentd/v2"
    "log/slog"
)

func main() {
    // docker-compose up -d
    client, err := fluent.New(fluent.Config{
        FluentHost:    "localhost",
        FluentPort:    24224,
        FluentNetwork: "tcp",
        MarshalAsJSON: true,
        Async:         true,
    })
    if err != nil {
        log.Fatal(err.Error())
    }


    logger := slog.New(
        slogfluentd.Option{
            Level: slog.LevelDebug,
            Client: client,
            Tag: "api",
        }.NewFluentdHandler(),
    )
    logger = logger.
        With("environment", "dev").
        With("release", "v1.0.0")

    // log error
    logger.
        With("tag", "api.sql").
        With("query.statement", "SELECT COUNT(*) FROM users;").
        With("query.duration", 1*time.Second).
        With("error", fmt.Errorf("could not count users")).
        Error("caramba!")

    // log user signup
    logger.
        With(
            slog.Group("user",
                slog.String("id", "user-123"),
                slog.Time("created_at", time.Now()),
            ),
        ).
        Info("user registration")
}

Output:

// tag: api.sql
{
    "timestamp":"2023-04-10T14:00:0.000000+00:00",
    "level":"ERROR",
    "message":"caramba!",
    "tag":"api.sql",
    "error":{
        "error":"could not count users",
        "kind":"*errors.errorString",
        "stack":null
    },
    "extra":{
        "environment":"dev",
        "release":"v1.0.0",
        "query.statement":"SELECT COUNT(*) FROM users;",
        "query.duration": "1s"
    }
}


// tag: api
{
    "timestamp":"2023-04-10T14:00:0.000000+00:00",
    "level":"INFO",
    "message":"user registration",
    "tag":"api",
    "error":null,
    "extra":{
        "environment":"dev",
        "release":"v1.0.0",
        "user":{
            "id":"user-123",
            "created_at":"2023-04-10T14:00:0.000000+00:00"
        }
    }
}

Tracing

Import the samber/slog-otel library.

import (
	slogfluentd "github.com/samber/slog-fluentd"
	slogotel "github.com/samber/slog-otel"
	"go.opentelemetry.io/otel/sdk/trace"
)

func main() {
	tp := trace.NewTracerProvider(
		trace.WithSampler(trace.AlwaysSample()),
	)
	tracer := tp.Tracer("hello/world")

	ctx, span := tracer.Start(context.Background(), "foo")
	defer span.End()

	span.AddEvent("bar")

	logger := slog.New(
		slogfluentd.Option{
			// ...
			AttrFromContext: []func(ctx context.Context) []slog.Attr{
				slogotel.ExtractOtelAttrFromContext([]string{"tracing"}, "trace_id", "span_id"),
			},
		}.NewFluentdHandler(),
	)

	logger.ErrorContext(ctx, "a message")
}

🤝 Contributing

• Ping me on twitter @samuelberthe (DMs, mentions, whatever :))
• Fork the project
• Fix open issues or request new features

Don't hesitate ;)

# Install some dev dependencies
make tools

# Run tests
make test
# or
make watch-test

👤 Contributors

💫 Show your support

Give a ⭐️ if this project helped you!

📝 License

Copyright © 2023 Samuel Berthe.

This project is MIT licensed.