Observability Support

Micrometer defines an Observation concept that enables both Metrics and Traces in applications. Metrics support offers a way to create timers, gauges, or counters for collecting statistics about the runtime behavior of your application. Metrics can help you to track error rates, usage patterns, performance, and more. Traces provide a holistic view of an entire system, crossing application boundaries; you can zoom in on particular user requests and follow their entire completion across applications.

Spring Framework instruments various parts of its own codebase to publish observations if an ObservationRegistry is configured. You can learn more about configuring the observability infrastructure in Spring Boot.

List of produced Observations

Spring Framework instruments various features for observability. As outlined at the beginning of this section, observations can generate timer Metrics and/or Traces depending on the configuration.

Table 1. Observations produced by Spring Framework
Observation name Description

"http.client.requests"

Time spent for HTTP client exchanges

"http.server.requests"

Processing time for HTTP server exchanges at the Framework level

"jms.message.publish"

Time spent sending a JMS message to a destination by a message producer.

"jms.message.process"

Processing time for a JMS message that was previously received by a message consumer.

"tasks.scheduled.execution"

Processing time for an execution of a @Scheduled task

Observations are using Micrometer’s official naming convention, but Metrics names will be automatically converted to the format preferred by the monitoring system backend (Prometheus, Atlas, Graphite, InfluxDB…​).

Micrometer Observation concepts

If you are not familiar with Micrometer Observation, here’s a quick summary of the concepts you should know about.

  • Observation is the actual recording of something happening in your application. This is processed by ObservationHandler implementations to produce metrics or traces.

  • Each observation has a corresponding ObservationContext implementation; this type holds all the relevant information for extracting metadata for it. In the case of an HTTP server observation, the context implementation could hold the HTTP request, the HTTP response, any exception thrown during processing, and so forth.

  • Each Observation holds KeyValues metadata. In the case of an HTTP server observation, this could be the HTTP request method, the HTTP response status, and so forth. This metadata is contributed by ObservationConvention implementations which should declare the type of ObservationContext they support.

  • KeyValues are said to be "low cardinality" if there is a low, bounded number of possible values for the KeyValue tuple (HTTP method is a good example). Low cardinality values are contributed to metrics only. Conversely, "high cardinality" values are unbounded (for example, HTTP request URIs) and are only contributed to traces.

  • An ObservationDocumentation documents all observations in a particular domain, listing the expected key names and their meaning.

Configuring Observations

Global configuration options are available at the ObservationRegistry#observationConfig() level. Each instrumented component will provide two extension points:

  • setting the ObservationRegistry; if not set, observations will not be recorded and will be no-ops

  • providing a custom ObservationConvention to change the default observation name and extracted KeyValues

Using custom Observation conventions

Let’s take the example of the Spring MVC "http.server.requests" metrics instrumentation with the ServerHttpObservationFilter. This observation uses a ServerRequestObservationConvention with a ServerRequestObservationContext; custom conventions can be configured on the Servlet filter. If you would like to customize the metadata produced with the observation, you can extend the DefaultServerRequestObservationConvention for your requirements:

import io.micrometer.common.KeyValue;
import io.micrometer.common.KeyValues;

import org.springframework.http.server.observation.DefaultServerRequestObservationConvention;
import org.springframework.http.server.observation.ServerRequestObservationContext;

public class ExtendedServerRequestObservationConvention extends DefaultServerRequestObservationConvention {

	@Override
	public KeyValues getLowCardinalityKeyValues(ServerRequestObservationContext context) {
		// here, we just want to have an additional KeyValue to the observation, keeping the default values
		return super.getLowCardinalityKeyValues(context).and(custom(context));
	}

	private KeyValue custom(ServerRequestObservationContext context) {
		return KeyValue.of("custom.method", context.getCarrier().getMethod());
	}

}

If you want full control, you can implement the entire convention contract for the observation you’re interested in:

import java.util.Locale;

import io.micrometer.common.KeyValue;
import io.micrometer.common.KeyValues;

import org.springframework.http.server.observation.ServerHttpObservationDocumentation;
import org.springframework.http.server.observation.ServerRequestObservationContext;
import org.springframework.http.server.observation.ServerRequestObservationConvention;

public class CustomServerRequestObservationConvention implements ServerRequestObservationConvention {

	@Override
	public String getName() {
		// will be used as the metric name
		return "http.server.requests";
	}

	@Override
	public String getContextualName(ServerRequestObservationContext context) {
		// will be used for the trace name
		return "http " + context.getCarrier().getMethod().toLowerCase(Locale.ROOT);
	}

	@Override
	public KeyValues getLowCardinalityKeyValues(ServerRequestObservationContext context) {
		return KeyValues.of(method(context), status(context), exception(context));
	}


	@Override
	public KeyValues getHighCardinalityKeyValues(ServerRequestObservationContext context) {
		return KeyValues.of(httpUrl(context));
	}

	private KeyValue method(ServerRequestObservationContext context) {
		// You should reuse as much as possible the corresponding ObservationDocumentation for key names
		return KeyValue.of(ServerHttpObservationDocumentation.LowCardinalityKeyNames.METHOD, context.getCarrier().getMethod());
	}

	// status(), exception(), httpUrl()...

	private KeyValue status(ServerRequestObservationContext context) {
		return KeyValue.of(ServerHttpObservationDocumentation.LowCardinalityKeyNames.STATUS, String.valueOf(context.getResponse().getStatus()));
	}

	private KeyValue exception(ServerRequestObservationContext context) {
		String exception = (context.getError() != null ? context.getError().getClass().getSimpleName() : KeyValue.NONE_VALUE);
		return KeyValue.of(ServerHttpObservationDocumentation.LowCardinalityKeyNames.EXCEPTION, exception);
	}

	private KeyValue httpUrl(ServerRequestObservationContext context) {
		return KeyValue.of(ServerHttpObservationDocumentation.HighCardinalityKeyNames.HTTP_URL, context.getCarrier().getRequestURI());
	}

}

You can also achieve similar goals using a custom ObservationFilter – adding or removing key values for an observation. Filters do not replace the default convention and are used as a post-processing component.

import io.micrometer.common.KeyValue;
import io.micrometer.observation.Observation;
import io.micrometer.observation.ObservationFilter;

import org.springframework.http.server.observation.ServerRequestObservationContext;

public class ServerRequestObservationFilter implements ObservationFilter {

	@Override
	public Observation.Context map(Observation.Context context) {
		if (context instanceof ServerRequestObservationContext serverContext) {
			context.setName("custom.observation.name");
			context.addLowCardinalityKeyValue(KeyValue.of("project", "spring"));
			String customAttribute = (String) serverContext.getCarrier().getAttribute("customAttribute");
			context.addLowCardinalityKeyValue(KeyValue.of("custom.attribute", customAttribute));
		}
		return context;
	}
}

You can configure ObservationFilter instances on the ObservationRegistry.

@Scheduled tasks instrumentation

An Observation is created for each execution of an @Scheduled task. Applications need to configure the ObservationRegistry on the ScheduledTaskRegistrar to enable the recording of observations. This can be done by declaring a SchedulingConfigurer bean that sets the observation registry:

import io.micrometer.observation.ObservationRegistry;

import org.springframework.scheduling.annotation.SchedulingConfigurer;
import org.springframework.scheduling.config.ScheduledTaskRegistrar;

public class ObservationSchedulingConfigurer implements SchedulingConfigurer {

	private final ObservationRegistry observationRegistry;

	public ObservationSchedulingConfigurer(ObservationRegistry observationRegistry) {
		this.observationRegistry = observationRegistry;
	}

	@Override
	public void configureTasks(ScheduledTaskRegistrar taskRegistrar) {
		taskRegistrar.setObservationRegistry(this.observationRegistry);
	}

}

It is using the org.springframework.scheduling.support.DefaultScheduledTaskObservationConvention by default, backed by the ScheduledTaskObservationContext. You can configure a custom implementation on the ObservationRegistry directly. During the execution of the scheduled method, the current observation is restored in the ThreadLocal context or the Reactor context (if the scheduled method returns a Mono or Flux type).

By default, the following KeyValues are created:

Table 2. Low cardinality Keys

Name

Description

code.function (required)

Name of Java Method that is scheduled for execution.

code.namespace (required)

Canonical name of the class of the bean instance that holds the scheduled method, or "ANONYMOUS" for anonymous classes.

error (required)

Class name of the exception thrown during the execution, or "none" if no exception happened.

exception (deprecated)

Duplicates the error key and might be removed in the future.

outcome (required)

Outcome of the method execution. Can be "SUCCESS", "ERROR" or "UNKNOWN" (if for example the operation was cancelled during execution).

JMS messaging instrumentation

Spring Framework uses the Jakarta JMS instrumentation provided by Micrometer if the io.micrometer:micrometer-jakarta9 dependency is on the classpath. The io.micrometer.jakarta9.instrument.jms.JmsInstrumentation instruments jakarta.jms.Session and records the relevant observations.

This instrumentation will create 2 types of observations:

  • "jms.message.publish" when a JMS message is sent to the broker, typically with JmsTemplate.

  • "jms.message.process" when a JMS message is processed by the application, typically with a MessageListener or a @JmsListener annotated method.

currently there is no instrumentation for "jms.message.receive" observations as there is little value in measuring the time spent waiting for the reception of a message. Such an integration would typically instrument MessageConsumer#receive method calls. But once those return, the processing time is not measured and the trace scope cannot be propagated to the application.

By default, both observations share the same set of possible KeyValues:

Table 3. Low cardinality Keys

Name

Description

error

Class name of the exception thrown during the messaging operation (or "none").

exception (deprecated)

Duplicates the error key and might be removed in the future.

messaging.destination.temporary (required)

Whether the destination is a TemporaryQueue or TemporaryTopic (values: "true" or "false").

messaging.operation (required)

Name of JMS operation being performed (values: "publish" or "process").

Table 4. High cardinality Keys

Name

Description

messaging.message.conversation_id

The correlation ID of the JMS message.

messaging.destination.name

The name of destination the current message was sent to.

messaging.message.id

Value used by the messaging system as an identifier for the message.

JMS message Publication instrumentation

"jms.message.publish" observations are recorded when a JMS message is sent to the broker. They measure the time spent sending the message and propagate the tracing information with outgoing JMS message headers.

You will need to configure the ObservationRegistry on the JmsTemplate to enable observations:

import io.micrometer.observation.ObservationRegistry;
import jakarta.jms.ConnectionFactory;

import org.springframework.jms.core.JmsMessagingTemplate;
import org.springframework.jms.core.JmsTemplate;

public class JmsTemplatePublish {

	private final JmsTemplate jmsTemplate;

	private final JmsMessagingTemplate jmsMessagingTemplate;

	public JmsTemplatePublish(ObservationRegistry observationRegistry, ConnectionFactory connectionFactory) {
		this.jmsTemplate = new JmsTemplate(connectionFactory);
		// configure the observation registry
		this.jmsTemplate.setObservationRegistry(observationRegistry);

		// For JmsMessagingTemplate, instantiate it with a JMS template that has a configured registry
		this.jmsMessagingTemplate = new JmsMessagingTemplate(this.jmsTemplate);
	}

	public void sendMessages() {
		this.jmsTemplate.convertAndSend("spring.observation.test", "test message");
	}

}

It uses the io.micrometer.jakarta9.instrument.jms.DefaultJmsPublishObservationConvention by default, backed by the io.micrometer.jakarta9.instrument.jms.JmsPublishObservationContext.

Similar observations are recorded with @JmsListener annotated methods when response messages are returned from the listener method.

JMS message Processing instrumentation

"jms.message.process" observations are recorded when a JMS message is processed by the application. They measure the time spent processing the message and propagate the tracing context with incoming JMS message headers.

Most applications will use the @JmsListener annotated methods mechanism to process incoming messages. You will need to ensure that the ObservationRegistry is configured on the dedicated JmsListenerContainerFactory:

import io.micrometer.observation.ObservationRegistry;
import jakarta.jms.ConnectionFactory;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.jms.annotation.EnableJms;
import org.springframework.jms.config.DefaultJmsListenerContainerFactory;

@Configuration
@EnableJms
public class JmsConfiguration {

	@Bean
	public DefaultJmsListenerContainerFactory jmsListenerContainerFactory(ConnectionFactory connectionFactory, ObservationRegistry observationRegistry) {
		DefaultJmsListenerContainerFactory factory = new DefaultJmsListenerContainerFactory();
		factory.setConnectionFactory(connectionFactory);
		factory.setObservationRegistry(observationRegistry);
		return factory;
	}

}

A default container factory is required to enable the annotation support, but note that @JmsListener annotations can refer to specific container factory beans for specific purposes. In all cases, Observations are only recorded if the observation registry is configured on the container factory.

Similar observations are recorded with JmsTemplate when messages are processed by a MessageListener. Such listeners are set on a MessageConsumer within a session callback (see JmsTemplate.execute(SessionCallback<T>)).

This observation uses the io.micrometer.jakarta9.instrument.jms.DefaultJmsProcessObservationConvention by default, backed by the io.micrometer.jakarta9.instrument.jms.JmsProcessObservationContext.

HTTP Server instrumentation

HTTP server exchange observations are created with the name "http.server.requests" for Servlet and Reactive applications.

Servlet applications

Applications need to configure the org.springframework.web.filter.ServerHttpObservationFilter Servlet filter in their application. It uses the org.springframework.http.server.observation.DefaultServerRequestObservationConvention by default, backed by the ServerRequestObservationContext.

This will only record an observation as an error if the Exception has not been handled by the web framework and has bubbled up to the Servlet filter. Typically, all exceptions handled by Spring MVC’s @ExceptionHandler and ProblemDetail support will not be recorded with the observation. You can, at any point during request processing, set the error field on the ObservationContext yourself:

import jakarta.servlet.http.HttpServletRequest;

import org.springframework.http.ResponseEntity;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.ExceptionHandler;
import org.springframework.web.filter.ServerHttpObservationFilter;

@Controller
public class UserController {

	@ExceptionHandler(MissingUserException.class)
	ResponseEntity<Void> handleMissingUser(HttpServletRequest request, MissingUserException exception) {
		// We want to record this exception with the observation
		ServerHttpObservationFilter.findObservationContext(request)
				.ifPresent(context -> context.setError(exception));
		return ResponseEntity.notFound().build();
	}

	static class MissingUserException extends RuntimeException {
	}

}
Because the instrumentation is done at the Servlet Filter level, the observation scope only covers the filters ordered after this one as well as the handling of the request. Typically, Servlet container error handling is performed at a lower level and won’t have any active observation or span. For this use case, a container-specific implementation is required, such as a org.apache.catalina.Valve for Tomcat; this is outside the scope of this project.

By default, the following KeyValues are created:

Table 5. Low cardinality Keys

Name

Description

error (required)

Class name of the exception thrown during the exchange, or "none" if no exception happened.

exception (deprecated)

Duplicates the error key and might be removed in the future.

method (required)

Name of HTTP request method or "none" if not a well-known method.

outcome (required)

Outcome of the HTTP server exchange.

status (required)

HTTP response raw status code, or "UNKNOWN" if no response was created.

uri (required)

URI pattern for the matching handler if available, falling back to REDIRECTION for 3xx responses, NOT_FOUND for 404 responses, root for requests with no path info, and UNKNOWN for all other requests.

Table 6. High cardinality Keys

Name

Description

http.url (required)

HTTP request URI.

Reactive applications

Applications need to configure the WebHttpHandlerBuilder with a MeterRegistry to enable server instrumentation. This can be done on the WebHttpHandlerBuilder, as follows:

import io.micrometer.observation.ObservationRegistry;

import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.http.server.reactive.HttpHandler;
import org.springframework.web.server.adapter.WebHttpHandlerBuilder;

@Configuration(proxyBeanMethods = false)
public class HttpHandlerConfiguration {

	private final ApplicationContext applicationContext;

	public HttpHandlerConfiguration(ApplicationContext applicationContext) {
		this.applicationContext = applicationContext;
	}

	@Bean
	public HttpHandler httpHandler(ObservationRegistry registry) {
		return WebHttpHandlerBuilder.applicationContext(this.applicationContext)
				.observationRegistry(registry)
				.build();
	}
}

It is using the org.springframework.http.server.reactive.observation.DefaultServerRequestObservationConvention by default, backed by the ServerRequestObservationContext.

This will only record an observation as an error if the Exception has not been handled by an application Controller. Typically, all exceptions handled by Spring WebFlux’s @ExceptionHandler and ProblemDetail support will not be recorded with the observation. You can, at any point during request processing, set the error field on the ObservationContext yourself:

import org.springframework.http.ResponseEntity;
import org.springframework.http.server.reactive.observation.ServerRequestObservationContext;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.ExceptionHandler;
import org.springframework.web.server.ServerWebExchange;

@Controller
public class UserController {

	@ExceptionHandler(MissingUserException.class)
	ResponseEntity<Void> handleMissingUser(ServerWebExchange exchange, MissingUserException exception) {
		// We want to record this exception with the observation
		ServerRequestObservationContext.findCurrent(exchange.getAttributes())
				.ifPresent(context -> context.setError(exception));
		return ResponseEntity.notFound().build();
	}

	static class MissingUserException extends RuntimeException {
	}

}

By default, the following KeyValues are created:

Table 7. Low cardinality Keys

Name

Description

error (required)

Class name of the exception thrown during the exchange, or "none" if no exception happened.

exception (deprecated)

Duplicates the error key and might be removed in the future.

method (required)

Name of HTTP request method or "none" if not a well-known method.

outcome (required)

Outcome of the HTTP server exchange.

status (required)

HTTP response raw status code, or "UNKNOWN" if no response was created.

uri (required)

URI pattern for the matching handler if available, falling back to REDIRECTION for 3xx responses, NOT_FOUND for 404 responses, root for requests with no path info, and UNKNOWN for all other requests.

Table 8. High cardinality Keys

Name

Description

http.url (required)

HTTP request URI.

HTTP Client Instrumentation

HTTP client exchange observations are created with the name "http.client.requests" for blocking and reactive clients. Unlike their server counterparts, the instrumentation is implemented directly in the client so the only required step is to configure an ObservationRegistry on the client.

RestTemplate

Applications must configure an ObservationRegistry on RestTemplate instances to enable the instrumentation; without that, observations are "no-ops". Spring Boot will auto-configure RestTemplateBuilder beans with the observation registry already set.

Instrumentation uses the org.springframework.http.client.observation.ClientRequestObservationConvention by default, backed by the ClientRequestObservationContext.

Table 9. Low cardinality Keys

Name

Description

method (required)

Name of HTTP request method or "none" if not a well-known method.

uri (required)

URI template used for HTTP request, or "none" if none was provided. Only the path part of the URI is considered.

client.name (required)

Client name derived from the request URI host.

status (required)

HTTP response raw status code, or "IO_ERROR" in case of IOException, or "CLIENT_ERROR" if no response was received.

outcome (required)

Outcome of the HTTP client exchange.

error (required)

Class name of the exception thrown during the exchange, or "none" if no exception happened.

exception (deprecated)

Duplicates the error key and might be removed in the future.

Table 10. High cardinality Keys

Name

Description

http.url (required)

HTTP request URI.

RestClient

Applications must configure an ObservationRegistry on the RestClient.Builder to enable the instrumentation; without that, observations are "no-ops".

Instrumentation uses the org.springframework.http.client.observation.ClientRequestObservationConvention by default, backed by the ClientRequestObservationContext.

Table 11. Low cardinality Keys

Name

Description

method (required)

Name of HTTP request method or "none" if the request could not be created.

uri (required)

URI template used for HTTP request, or "none" if none was provided. Only the path part of the URI is considered.

client.name (required)

Client name derived from the request URI host.

status (required)

HTTP response raw status code, or "IO_ERROR" in case of IOException, or "CLIENT_ERROR" if no response was received.

outcome (required)

Outcome of the HTTP client exchange.

error (required)

Class name of the exception thrown during the exchange, or "none" if no exception happened.

exception (deprecated)

Duplicates the error key and might be removed in the future.

Table 12. High cardinality Keys

Name

Description

http.url (required)

HTTP request URI.

WebClient

Applications must configure an ObservationRegistry on the WebClient builder to enable the instrumentation; without that, observations are "no-ops". Spring Boot will auto-configure WebClient.Builder beans with the observation registry already set.

Instrumentation uses the org.springframework.web.reactive.function.client.ClientRequestObservationConvention by default, backed by the ClientRequestObservationContext.

Table 13. Low cardinality Keys

Name

Description

method (required)

Name of HTTP request method or "none" if not a well-known method.

uri (required)

URI template used for HTTP request, or "none" if none was provided. Only the path part of the URI is considered.

client.name (required)

Client name derived from the request URI host.

status (required)

HTTP response raw status code, or "IO_ERROR" in case of IOException, or "CLIENT_ERROR" if no response was received.

outcome (required)

Outcome of the HTTP client exchange.

error (required)

Class name of the exception thrown during the exchange, or "none" if no exception happened.

exception (deprecated)

Duplicates the error key and might be removed in the future.

Table 14. High cardinality Keys

Name

Description

http.url (required)

HTTP request URI.

Application Events and @EventListener

Spring Framework does not contribute Observations for @EventListener calls, as they don’t have the right semantics for such instrumentation. By default, event publication and processing are done synchronously and on the same thread. This means that during the execution of that task, the ThreadLocals and logging context will be the same as the event publisher.

If the application globally configures a custom ApplicationEventMulticaster with a strategy that schedules event processing on different threads, this is no longer true. All @EventListener methods will be processed on a different thread, outside the main event publication thread. In these cases, the Micrometer Context Propagation library can help propagate such values and better correlate the processing of the events. The application can configure the chosen TaskExecutor to use a ContextPropagatingTaskDecorator that decorates tasks and propagates context. For this to work, the io.micrometer:context-propagation library must be present on the classpath:

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.event.SimpleApplicationEventMulticaster;
import org.springframework.core.task.SimpleAsyncTaskExecutor;
import org.springframework.core.task.support.ContextPropagatingTaskDecorator;

@Configuration
public class ApplicationEventsConfiguration {

	@Bean(name = "applicationEventMulticaster")
	public SimpleApplicationEventMulticaster simpleApplicationEventMulticaster() {
		SimpleApplicationEventMulticaster eventMulticaster = new SimpleApplicationEventMulticaster();
		SimpleAsyncTaskExecutor taskExecutor = new SimpleAsyncTaskExecutor();
		// decorate task execution with a decorator that supports context propagation
		taskExecutor.setTaskDecorator(new ContextPropagatingTaskDecorator());
		eventMulticaster.setTaskExecutor(taskExecutor);
		return eventMulticaster;
	}

}

Similarly, if that asynchronous choice is made locally for each @EventListener annotated method, by adding @Async to it, you can choose a TaskExecutor that propagates context by referring to it by its qualifier. Given the following TaskExecutor bean definition, configured with the dedicated task decorator:

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.core.task.SimpleAsyncTaskExecutor;
import org.springframework.core.task.TaskExecutor;
import org.springframework.core.task.support.ContextPropagatingTaskDecorator;

@Configuration
public class EventAsyncExecutionConfiguration {

	@Bean(name = "propagatingContextExecutor")
	public TaskExecutor propagatingContextExecutor() {
		SimpleAsyncTaskExecutor taskExecutor = new SimpleAsyncTaskExecutor();
		// decorate task execution with a decorator that supports context propagation
		taskExecutor.setTaskDecorator(new ContextPropagatingTaskDecorator());
		return taskExecutor;
	}

}

Annotating event listeners with @Async and the relevant qualifier will achieve similar context propagation results:

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import org.springframework.context.event.EventListener;
import org.springframework.scheduling.annotation.Async;
import org.springframework.stereotype.Component;

@Component
public class EmailNotificationListener {

	private final Log logger = LogFactory.getLog(EmailNotificationListener.class);

	@EventListener(EmailReceivedEvent.class)
	@Async("propagatingContextExecutor")
	public void emailReceived(EmailReceivedEvent event) {
		// asynchronously process the received event
		// this logging statement will contain the expected MDC entries from the propagated context
		logger.info("email has been received");
	}

}