Prometheus config doesn't work with Spring boot 2.3.0: ClassNotFoundException: io.micrometer.prometheus.HistogramFlavor

Application was working correctly with version 2.2.6 but as the application is upgraded to latest version of spring boot 2.3.0 it stopped working and fails during startup.

2020-05-20T08:43:04.408+01:00 [APP/PROC/WEB/0] [OUT] 2020-05-20 07:43:04.407 ERROR 15 --- [ main] o.s.b.web.embedded.tomcat.TomcatStarter : Error starting Tomcat context. 
Exception: org.springframework.beans.factory.UnsatisfiedDependencyException. Message: Error creating bean with name 'webMvcMetricsFilter' defined in class path resource [org/springframework/boot/actuate/autoconfigure/metrics/web/servlet/WebMvcMetricsAutoConfiguration.class]: 
    Unsatisfied dependency expressed through method 'webMvcMetricsFilter' parameter 0; 
nested exception is org.springframework.beans.factory.UnsatisfiedDependencyException: 
    Error creating bean with name 'compositeMeterRegistry' defined in class path resource [org/springframework/boot/actuate/autoconfigure/metrics/CompositeMeterRegistryConfiguration.class]: 
    Unsatisfied dependency expressed through method 'compositeMeterRegistry' parameter 1; 
nested exception is org.springframework.beans.factory.UnsatisfiedDependencyException: 
    Error creating bean with name 'prometheusMeterRegistry' defined in class path resource [org/springframework/boot/actuate/autoconfigure/metrics/export/prometheus/PrometheusMetricsExportAutoConfiguration.class]: 
    Unsatisfied dependency expressed through method 'prometheusMeterRegistry' parameter 0; 
nested exception is org.springframework.beans.factory.UnsatisfiedDependencyException: 
    Error creating bean with name 'prometheusConfig' defined in class path resource [org/springframework/boot/actuate/autoconfigure/metrics/export/prometheus/PrometheusMetricsExportAutoConfiguration.class]: 
    Unsatisfied dependency expressed through method 'prometheusConfig' parameter 0; 
nested exception is org.springframework.beans.factory.BeanCreationException: 
    Error creating bean with name 'management.metrics.export.prometheus-org.springframework.boot.actuate.autoconfigure.metrics.export.prometheus.PrometheusProperties': 
    Lookup method resolution failed; 
nested exception is java.lang.IllegalStateException: 
    Failed to introspect Class [org.springframework.boot.actuate.autoconfigure.metrics.export.prometheus.PrometheusProperties] from ClassLoader [org.springframework.boot.loader.LaunchedURLClassLoader@4f3f5b24]

Can see below class not found exception at the bottom of start trace.

In your particular case the micrometer-registry-prometheus must be in-line with spring boot's micrometer-core's version. It is 1.5.1 because Spring Boot (Actuator) pulls that dependency in with version 2.3.0.

dependencies {
  implementation group: 'io.micrometer', name: 'micrometer-registry-prometheus', version: '1.5.1'
}