Improve configuration support for Observability integration.

Closes: #4216

src/main/asciidoc/reference/observability.adoc

@@ -8,3 +8,87 @@ include::{root-target}_conventions.adoc[]
 include::{root-target}_metrics.adoc[]
 
 include::{root-target}_spans.adoc[]
+
+[[observability.registration]]
+== Observability Registration
+
+Spring Data MongoDB currently has the most up-to-date code to support Observability in your MongoDB application.
+These changes, however, haven't been picked up by Spring Boot (yet).
+Until those changes are applied, if you wish to use Spring Data MongoDB's flavor of Observability, you must carry out the following steps.
+
+. First of all, you must opt into Spring Data MongoDB's configuration settings by adding the `@EnableMongoObservability` to either your `@SpringBootApplication` class or one of your configuration classes.
+. Your project must include *Spring Boot Actuator*.
+. Next you must add one of the following bean definitions based on whether you're using non-reactive or reactive Spring Data MongoDB.
++
+.Registering a synchronous (non-reactive) MongoDB Micrometer setup
+====
+[source,java]
+----
+@Bean
+MongoClientSettingsBuilderCustomizer mongoMetricsSynchronousContextProvider(Tracer tracer,
+        ObservationRegistry registry) {
+    return (clientSettingsBuilder) -> {
+        clientSettingsBuilder.contextProvider( //
+                MongoMetricsConfigurationHelper.synchronousContextProvider(tracer, registry));
+    };
+}
+----
+====
++
+.Registering a reactive MongoDB Micrometer setup
+====
+[source,java]
+----
+@Bean
+MongoClientSettingsBuilderCustomizer mongoMetricsReactiveContextProvider(ObservationRegistry registry) {
+    return (clientSettingsBuilder) -> {
+        clientSettingsBuilder.contextProvider( //
+                MongoMetricsReactiveConfigurationHelper.reactiveContextProvider(registry));
+    };
+}
+----
+====
++
+IMPORTANT: ONLY add one of these two bean definitions!
+. Add the following bean definition to listen for MongoDB command events and record them with Micrometer.
++
+.Registering to listen for MongoDB commands.
+====
+[source,java]
+----
+@Bean
+MongoClientSettingsBuilderCustomizer mongoObservationCommandListenerCustomizer(MongoDBContainer mongoDBContainer,
+        MongoObservationCommandListener commandListener) {
+    return (clientSettingsBuilder) -> clientSettingsBuilder //
+            .addCommandListener(commandListener);
+}
+----
+====
+. Add the following bean definition to register Spring Data MongoDB's trace observation handler
++
+.Registering
+====
+[source,java]
+----
+@Bean
+ObservationRegistryCustomizer<ObservationRegistry> mongoTracingHandlerCustomizer(
+        MongoTracingObservationHandler handler) {
+    return handler::register;
+}
+----
+====
+. Disable Spring Boot's autoconfigured MongoDB command listener and enable tracing manually by adding the following properties to your `application.properties`
++
+.Custom settings to apply
+====
+[source]
+----
+# Disable Spring Boot's autoconfigured tracing
+management.metrics.mongo.command.enabled=false
+# Enable it manually
+management.tracing.enabled=true
+----
+Be sure to add any other relevant settings needed to configure the tracer you are using based upon Micrometer's reference documentation.
+====
+
+This should do it! You are now running with Spring Data MongoDB's usage of Spring Observability's `Observation` API.