⚠️ If you are upgrading to 0.14.0 please read the migration guide.

Yet another distributed tracing system, this time just for Scala. Heavily relies upon Cats and Cats Effect.

Compatible with OpenTelemetry and Jaeger, based on, and interoperates with Natchez.

Obligatory XKCD

• Motivation
• Highlights
• Quickstart
• Migrating to 0.14.0
• Repositories
• Components
• Documentation
• SBT Dependencies
• native-image Compatibility
• Contributing

It increasingly seems that Java tracing libraries are dependent on gRPC, which usually brings along lots of other dependencies. You may find Trace4Cats useful if you want to...

• Reduce the number of dependencies in your application
• Resolve a dependency conflict caused by a tracing implementation
• Create a native-image using GraalVM

Trace4Cats supports publishing spans to the following systems:

• Jaeger via Thrift over UDP and Protobuf over gRPC
• OpenTelemetry via Protobuf over gRPC and JSON over HTTP
• Log using Log4Cats
• Trace4Cats Avro over UDP, TCP and Kafka
• Google Cloud Trace over HTTP and gRPC
• Datadog over HTTP
• New Relic over HTTP
• Zipkin over HTTP

Instrumentation for trace propagation and continuation is available for the following libraries:

• Http4s client and server
• Sttp client v3
• Tapir
• FS2 Kafka consumer and producer
• FS2

Unlike other tracing libraries, trace attributes are lazily evaluated. If a span is not sampled, no computation associated with calculating attribute values will be performed.

More information on how to use these can be found in the examples documentation.

For more see the documentation and more advanced examples.

Add the following dependencies to your build.sbt:

"io.janstenpickle" %% "trace4cats-core" % "0.14.0"
"io.janstenpickle" %% "trace4cats-avro-exporter" % "0.14.0"

Then run the collector in span logging mode:

echo "log-spans: true" > /tmp/collector.yaml
docker run -p7777:7777 -p7777:7777/udp -it \
  -v /tmp/collector.yaml:/tmp/collector.yaml \
  janstenpickle/trace4cats-collector-lite:0.14.0 \
  --config-file=/tmp/collector.yaml

Finally, run the following code to export some spans to the collector:

import cats.Monad
import cats.data.Kleisli
import cats.effect._
import cats.effect.std.Console
import cats.implicits._
import trace4cats._
import trace4cats.avro.AvroSpanCompleter

import scala.concurrent.duration._

object Trace4CatsQuickStart extends IOApp.Simple {
  def entryPoint[F[_]: Async](process: TraceProcess): Resource[F, EntryPoint[F]] =
    AvroSpanCompleter.udp[F](process, config = CompleterConfig(batchTimeout = 50.millis)).map { completer =>
      EntryPoint[F](SpanSampler.always[F], completer)
    }

  def runF[F[_]: Monad: Console: Trace]: F[Unit] =
    for {
      _ <- Trace[F].span("span1")(Console[F].println("trace this operation"))
      _ <- Trace[F].span("span2", SpanKind.Client)(Console[F].println("send some request"))
      _ <- Trace[F].span("span3", SpanKind.Client)(
        Trace[F].putAll("attribute1" -> "test", "attribute2" -> 200) >>
          Trace[F].setStatus(SpanStatus.Cancelled)
      )
    } yield ()

  def run: IO[Unit] =
    entryPoint[IO](TraceProcess("trace4cats")).use { ep =>
      ep.root("this is the root span").use { span =>
        runF[Kleisli[IO, Span[IO], *]].run(span)
      }
    }
}

Version 0.14.0 introduced a reworked module and package structure that reduced the number of dependencies and imports required to get started quickly. Effectively import trace4cats._ is all you should need to import throughout most of your codebase.

See the migration guide for information on how to migrate.

Trace4Cats is separated into a few repositories:

• trace4cats-avro Avro codecs, TCP/UDP server and exporter
• trace4cats-avro-kafka Avro Kafka exporter and consumer
• trace4cats-cloudtrace Google Cloud Trace exporters
• trace4cats-components standalone Trace4Cats components
• trace4cats-datadog Datadog exporters
• trace4cats-docs documentation and examples
• trace4cats-dynamic-extras extra utilities for dynamically configuring Trace4Cats
• trace4cats-exporter-http HTTP span exporter
• trace4cats-http4s Http4s client and server integrations
• trace4cats-jaeger Jaeger exporters
• trace4cats-jaeger-integration-test Integration test for exporters to Jaeger
• trace4cats-kafka FS2 Kafka integrations
• trace4cats-natchez Natchez integrations
• trace4cats-newrelic New Relic exporters
• trace4cats-opentelemetry OpenTelemetry exporters
• trace4cats-sttp Sttp client and Tapir integrations
• trace4cats-tail-sampling-extras extra utilities for tail sampling
• trace4cats-zipkin Zipkin exporters
• trace4cats-zio ZIO implementations of Trace4Cats typeclasses

Trace4Cats is made up as both a set of libraries for integration in applications and standalone processes. For information on the libraries and interfaces see the design documentation.

The standalone components are the agent and the collector. To see how they work together, see the topologies documentation, for information on configuring and running the agent and collector see the components documentation.

The source code for these components is located in the trace4cats-components repository.

• Design - Trace4Cats design
• Components - running and configuring Trace4Cats components
• Topologies - information on potential Trace4Cats deployment topologies
• Sampling - trace sampling
• Filtering - span attribute filtering
• Examples - code usage examples

To use Trace4Cats within your application add the dependencies listed below as needed:

"io.janstenpickle" %% "trace4cats-core" % "0.14.0"
"io.janstenpickle" %% "trace4cats-rate-sampling" % "0.14.0"
"io.janstenpickle" %% "trace4cats-fs2" % "0.14.0"
"io.janstenpickle" %% "trace4cats-http4s-client" % "0.14.0"
"io.janstenpickle" %% "trace4cats-http4s-server" % "0.14.0"
"io.janstenpickle" %% "trace4cats-sttp-client3" % "0.14.0"
"io.janstenpickle" %% "trace4cats-sttp-tapir" % "0.14.0"
"io.janstenpickle" %% "trace4cats-natchez" % "0.14.0"
"io.janstenpickle" %% "trace4cats-avro-exporter" % "0.14.0"
"io.janstenpickle" %% "trace4cats-avro-kafka-exporter" % "0.14.0"
"io.janstenpickle" %% "trace4cats-avro-kafka-consumer" % "0.14.0"
"io.janstenpickle" %% "trace4cats-jaeger-thrift-exporter" % "0.14.0"
"io.janstenpickle" %% "trace4cats-opentelemetry-otlp-grpc-exporter" % "0.14.0"
"io.janstenpickle" %% "trace4cats-opentelemetry-otlp-http-exporter" % "0.14.0"
"io.janstenpickle" %% "trace4cats-opentelemetry-jaeger-exporter" % "0.14.0"
"io.janstenpickle" %% "trace4cats-stackdriver-grpc-exporter" % "0.14.0"
"io.janstenpickle" %% "trace4cats-stackdriver-http-exporter" % "0.14.0"
"io.janstenpickle" %% "trace4cats-datadog-http-exporter" % "0.14.0"
"io.janstenpickle" %% "trace4cats-newrelic-http-exporter" % "0.14.0"
"io.janstenpickle" %% "trace4cats-zipkin-http-exporter" % "0.14.0"

The following span completers have been found to be compatible with native-image:

• Trace4Cats Avro
• Jaeger Thrift over UDP
• OpenTelemetry JSON over HTTP
• Log
• Google Cloud Trace over HTTP
• Datadog over HTTP
• New Relic over HTTP
• Zipkin over HTTP

This project supports the Scala Code of Conduct and aims that its channels (mailing list, Gitter, github, etc.) to be welcoming environments for everyone.