Document OpenTelemetry configuration

Author: lukaszkorecki

README.md

@@ -37,7 +37,7 @@
 ;; pass a context map to add structured data to the message
 (log/info "hi!" {:foo "bar" :baz "qux"})
 
-;; context can be set 
+;; context can be set
 (log/with-context {:action "vibe-check"}
   (log/debug "checking the vibes")
   (let [are-you-ok? (do-the-vibe-check)]
@@ -70,7 +70,7 @@ Second part of ensuring that right things are logged and we keep a good performa
 
 ### How does it work?
 
-Mokujin wraps `clojure.tools.logging` and injects SLF4J's MDC into logging events, if provided. 
+Mokujin wraps `clojure.tools.logging` and injects SLF4J's MDC into logging events, if provided.
 Keep in mind that `infof` (and friends) variants are present, but do not support passing the MDC (more on that later).
 
 
@@ -138,7 +138,7 @@ Second difference is that only 1- and 2-arity (or in case of `log/error` 3-arity
 (log/info "hello" "there" "world")
 ```
 
-To help with migration and good log hygine Mokujin ships with custom hooks for `clj-kondo` and 
+To help with migration and good log hygine Mokujin ships with custom hooks for `clj-kondo` and
 report warnings in case of suspicious or incompatible call styles are detected.
 
 
@@ -271,6 +271,32 @@ This way we can delegate things like redacting MDC or async appenders to Logback
 
 Check `:mokujin.logback/json-async` configuration preset for a good example of how to set up async appenders with MDC support.
 
+
+#### Open Telemetry
+
+
+Open Telemetry supports automatic instrumentation of logging frameworks including Logback. To enable it, you need to:
+
+- start your application with the Open Telemetry Java agent
+- ensure that following environement variables are set:
+
+```
+export OTEL_INSTRUMENTATION_LOGBACK_APPENDER_EXPERIMENTAL_CAPTURE_LOGGER_CONTEXT_ATTRIBUTES=true
+export OTEL_INSTRUMENTATION_LOGBACK_APPENDER_EXPERIMENTAL_CAPTURE_MDC_ATTRIBUTES=*
+```
+
+alternatively, you can set these properties via JVM options:
+
+```
+-Dotel.instrumentation.logback.appender.experimental.capture.logger.context.attributes=true
+-Dotel.instrumentation.logback.appender.experimental.capture.mdc.attributes=*
+```
+
+
+From there, Open Telemetry will automatically capture MDC attributes and attach them to spans, inject trace IDs etc.
+
+
+
 ## TODO
 
 - [x] Maven release