Clj Otel

= clj-otel :icons: font ifdef::env-github[] :tip-caption: :bulb: :note-caption: :information_source: :important-caption: :heavy_exclamation_mark: :caution-caption: :fire: :warning-caption: :warning: endif::[]

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clj-otel provides a small idiomatic Clojure API for adding telemetry to your libraries and applications using https://opentelemetry.io/[OpenTelemetry], an emerging standard for telemetry in cloud-native software, enabling effective observability.

.A distributed trace displayed in https://www.honeycomb.io/[Honeycomb] image::doc/images/honeycomb-trace.png[Distributed trace displayed in Honeycomb,width=600,link="doc/images/honeycomb-trace.png?raw=true"]

.Metrics for an HTTP server route displayed on a https://grafana.com/[Grafana] dashboard image::doc/images/grafana-dashboard.png[Metrics displayed in Grafana,width=600,link="doc/images/grafana-dashboard.png?raw=true"]

== Requirements

clj-otel requires Clojure 1.10.3 or higher and is based on https://github.com/open-telemetry/opentelemetry-java[OpenTelemetry for Java], which supports Java 8 and higher.

== Quickstart

clj-otel is highly configurable and may be used in many ways. This quickstart briefly outlines getting started in a local environment. Find more in-depth information on clj-otel in the xref:_documentation[documentation] and xref:_examples[examples].

• To add manual instrumentation to your library or application at design time ** Add project dependency

.deps.edn [source,clojure]

{;; ... :deps {com.github.steffan-westcott/clj-otel-api {:mvn/version "0.2.10"}}}

** To add traces telemetry, use Clojure functions such as https://cljdoc.org/d/com.github.steffan-westcott/clj-otel-api/CURRENT/api/steffan-westcott.clj-otel.api.trace.span#with-span![steffan-westcott.clj-otel.api.trace.span/with-span!] to create spans with attributes + [source,clojure]

(defn validate-profile [profile] (span/with-span! ["Validating profile" {:system/profile-id (:id profile)}] (validate profile)))

** To add metrics telemetry, use Clojure functions in https://cljdoc.org/d/com.github.steffan-westcott/clj-otel-api/CURRENT/api/steffan-westcott.clj-otel.api.metrics.instrument[steffan-westcott.clj-otel.api.metrics.instrument] to create instruments, then add or record measurements with attributes + [source,clojure]

(defonce set-password-failure-count (instrument/instrument {:name "app.set-password-failure-count" :instrument-type :counter}))

(instrument/add! set-password-failure-count {:value 1 :attributes {:reason :too-short}})

** To add logs telemetry, use a logging library that exports an OpenTelemetry logs signal. https://logging.apache.org/log4j/2.x/[Log4J], https://logback.qos.ch/[Logback] and https://github.com/taoensso/timbre[Timbre] are logging libraries that support OpenTelemetry. clj-otel provides customized Log4J and Logback appenders that support asynchronous applications.

• To export telemetry data (from both manual and automatic instrumentation) from an application at runtime ** Download the latest OpenTelemetry instrumentation JAR opentelemetry-javaagent.jar from the https://github.com/open-telemetry/opentelemetry-java-instrumentation/releases[OpenTelemetry instrumentation agent releases page]. ** Add the following JVM options to your application, assuming export of traces telemetry only to an OTLP compliant backend such as https://www.jaegertracing.io/[Jaeger]

"-javaagent:opentelemetry-javaagent.jar" "-Dotel.service.name=NAME-OF-YOUR-SERVICE" "-Dotel.metrics.exporter=none" "-Dotel.logs.exporter=none"

• To receive exported telemetry data ** Prepare a telemetry backend such as Jaeger

[source,bash]

docker run --rm
-p 16686:16686
-p 4318:4318
jaegertracing/jaeger:2.11.0

• To explore application behaviour described by the received telemetry data ** Use telemetry backend features such as the Jaeger user interface at http://localhost:16686/search

NOTE: For demonstration configurations that export traces, metrics and logs telemetry, see the xref:_examples[examples].

[#_documentation] == Documentation

• link:doc/tutorial.adoc[Tutorial] : A walk-through of instrumenting a small Clojure program and viewing its telemetry.
• link:doc/guides.adoc[Guides] : Common task recipes for adding telemetry to your Clojure libraries and applications, then configuring and running applications with telemetry.
• link:doc/reference.adoc[API & Reference] : API documentation for all clj-otel modules.
• link:doc/concepts.adoc[Concepts] : A primer on observability, OpenTelemetry and what this project clj-otel enables for Clojure libraries and applications.

[#_examples] == Examples

Find complete example applications in the examples directory. The examples aim to show:

• Adding automatic and manual instrumentation to applications
• Configuring and running applications that export telemetry data
• Viewing telemetry data in backends

See more xref:doc/examples.adoc[information on configuring and running the examples].

== Project status

• clj-otel is currently used in a small number of independent production settings. Breaking API changes may still be made, but there should be few, if any.
• For manual instrumentation: ** Coverage of the Traces API is complete. *** Trace semantics conventions support for https://github.com/open-telemetry/semantic-conventions/blob/main/docs/exceptions/exceptions-spans.md[recording exceptions] is complete. *** Trace semantics support for https://github.com/open-telemetry/semantic-conventions/blob/main/docs/http/http-spans.md[HTTP spans] in applications run without the OpenTelemetry instrumentation agent is limited. *** Support for wrapping asynchronous Clojure code in spans is complete. There is support for core.async channels, CompletableFuture, Manifold deferreds, Missionary tasks and a callback API. The examples include applications using core.async with https://github.com/xadecimal/async-style[async-style], CompletableFuture with https://github.com/mpenet/auspex/[auspex], https://github.com/funcool/promesa[promesa] and https://github.com/igrishaev/whew[whew], https://github.com/clj-commons/manifold[Manifold] deferreds and https://github.com/leonoel/missionary[Missionary] tasks. There is also a demonstration https://clojure.github.io/core.async/index.html[core.async.flow] instrumented application. ** Coverage of the Metrics API is complete. *** Metrics HTTP semantics support for applications run without the OpenTelemetry instrumentation agent is very limited. ** Coverage of Logs API is complete. Note that the Logs API is for use by logging libraries only. For applications and general libraries, use a logging library with OpenTelemetry logging signal support, such as Log4j2, Timbre etc. These logging libraries support current context only.
• For the programmatic configuration of the OpenTelemetry SDK: ** Coverage of Traces TracerProvider is complete. ** Coverage of Metrics MeterProvider is in progress. Most configuration options are supported. ** Coverage of Logs LoggerProvider has been implemented.
• Some investigation of ContextStorageProvider has been done, as a possible route to make entire Java applications bound context aware. However, problems with instrumentation agent integration have ruled this out.

== TODO

• For manual instrumentation: ** Consider implementing a lightweight logging library that targets solely the Logs API. Also, add this logging library as a backend for https://github.com/taoensso/trove[Trove]. This will enable applications to make full use of the Logs API, which is not possible with other logging libraries. ** Consider supporting more https://github.com/open-telemetry/semantic-conventions/blob/main/docs/general/trace.md[trace semantics conventions].
• Maintain parity with the latest version of https://github.com/open-telemetry/opentelemetry-java[opentelemetry-java].
• Implement integration tests using https://github.com/javahippie/clj-test-containers[clj-test-containers] or similar.
• Consider ClojureScript OpenTelemetry support in the browser and node.js using https://github.com/open-telemetry/opentelemetry-js[opentelemetry-js]; this will likely be a separate project.

== Changelog

See xref:CHANGELOG.adoc[changelog]

== Contributing & contact

The most needed contribution is experience reports of clj-otel use in production systems. I am keen to hear of usages of clj-otel and any problems and successes. clj-otel is a very young project, so now is an ideal time to provide feedback on the API design as improvements can be made freely.

I will be happy to consider pull requests for minor changes, but I may not accept more significant changes while I make a start on some items in the TODO list.

For questions or feedback on clj-otel, contact me on the https://clojurians.slack.com/messages/clj-otel[#clj-otel] channel in http://clojurians.net/[Clojurians Slack], user steffan.

== Development

=== Requirements

To develop clj-otel, you should first install the following tools:

• https://clojure.org/guides/deps_and_cli[Clojure CLI tools]
• https://github.com/clj-kondo/clj-kondo/blob/master/doc/install.md[clj-kondo executable binary]
• https://github.com/kkinnear/zprint#get-zprint[zprint executable binary] (1.3.0 or later)

=== Developing

• Get information on available build scripts with this command:

[source,bash]

clojure -A:deps -T:build help/doc

• Before making any pull requests, please ensure the source code has been linted and formatted with these commands:

[source,bash]

clojure -T:build lint clojure -T:build fmt

== Acknowledgements

I want to thank:

• You (yes, you) for having the curiosity to look into this project. Thank you.
• My friends Golnaz and Nimmo, for pointing me in the direction of observability and OpenTelemetry. Without them, I wouldn't have had the idea to do this project.
• The OpenTelemetry community and all makers of telemetry backends for making the effective observability of systems a tangible reality. Cloud-native software is so complex now, we need all the help we can get to understand how well it is (or is not) working.
• The https://diataxis.fr/[Diátaxis Documentation Framework], for a simple way to structure technical documentation.

== License

Copyright © 2021-2026 Steffan Westcott + Distributed under the http://www.apache.org/licenses/LICENSE-2.0[Apache License v2.0]