Disable Tomcat's MBean Registry by default

Closes gh-16498

spring-boot-project/spring-boot-docs/src/main/asciidoc/howto.adoc

@@ -1075,6 +1075,20 @@ include::{code-examples}/context/embedded/TomcatLegacyCookieProcessorExample.jav
 
 
 
+[[howto-enable-tomcat-mbean-registry]]
+=== Enable Tomcat's MBean Registry
+Embedded Tomcat's MBean registry is disabled by default. This minimizes Tomcat's memory
+footprint. If you want to use Tomcat's MBeans, for example so that they can be used to
+expose metrics via Micrometer, you must use the `server.tomcat.mbeanregistry.enabled`
+property to do so, as shown in the following example:
+
+[source,properties,indent=0]
+----
+server.tomcat.mbeanregistry.enabled=true
+----
+
+
+
 [[howto-enable-multiple-listeners-in-undertow]]
 === Enable Multiple Listeners with Undertow
 Add an `UndertowBuilderCustomizer` to the `UndertowServletWebServerFactory` and

spring-boot-project/spring-boot-docs/src/main/asciidoc/production-ready-features.adoc

@@ -1793,7 +1793,8 @@ Spring Boot registers the following core metrics when applicable:
 * Logback metrics: record the number of events logged to Logback at each level
 * Uptime metrics: report a gauge for uptime and a fixed gauge representing the
 application's absolute start time
-* Tomcat metrics
+* Tomcat metrics (`server.tomcat.mbeanregistry.enabled` must be set to `true` for all
+Tomcat metrics to be registered)
 * https://docs.spring.io/spring-integration/docs/current/reference/html/system-management-chapter.html#micrometer-integration[Spring Integration] metrics