MeterFilters and MeterRegistryCustomizers are not ordered

[shakuzen]

#11843 applies MeterFilter beans, but the user cannot control the order in which the MeterFilters are applied, which may matter depending on what all the MeterFilters do.

For instance, I would like to turn on percentile histograms for my application's endpoints, but I want them off for all Actuator endpoints and unmapped requests because this adds ~70 time series for each endpoint per instance (and per status/exception!). My initial thought was to use the property management.metrics.distribution.percentiles-histogram like below.

management:
  metrics:
    distribution:
      percentiles-histogram:
        http.server.requests: true

Then I would only need to make a MeterFilter to turn this off if the uri tag seemed like an Actuator request (since there isn't a more direct way to do this without #13435) or unmapped request:

@Bean
MeterFilter noActuatorHistogramsFilter() {
	return new MeterFilter() {
		@Override
		public DistributionStatisticConfig configure(Meter.Id id, DistributionStatisticConfig config) {
			if ("http.server.requests".equals(id.getName()) && id.getTag("uri") != null && (id.getTag("uri").contains("actuator") || id.getTag("uri").equals("/**"))) {
				return DistributionStatisticConfig.builder()
						.percentilesHistogram(false)
						.build()
						.merge(config);
			}
			return config;
		}
	};
}

Looking at the MetricsAutoConfiguration class and seeing that the PropertiesMeterFilter has an @Order(0), I thought my custom MeterFilter bean would be applied after it, but this was not the case.

spring-boot/spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/metrics/MetricsAutoConfiguration.java

Lines 57 to 61 in a170bfc

	@Bean
	@Order(0)
	public PropertiesMeterFilter propertiesMeterFilter(MetricsProperties properties) {
	return new PropertiesMeterFilter(properties);
	}

The way I can work around this is to not use the property-based meter filter at all and just put all the logic I want in my own MeterFilter, but I think being able to control of the order of MeterFilter is a generally good idea regardless of this specific use-case.

[wilkinsona]

MeterRegistryCustomizer beans have the same problem due to the way both they and MeterFilter beans are retrieved by MeterRegistryPostProcessor.

This issue's currently targeted at 2.1. I wonder if we should fix it in 2.0.x?

[philwebb]

I'll move it back to 2.0.x