Spring Boot Webflux + Elastic APM Monitoring - spring

Question

I am currently new to Elastic APM.
I am currently developing an application using spring-webflux and want to monitor my application using Elastic APM, but unfortunately, it's not working for me.
Dependecies
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.2.6.RELEASE</version>
</parent>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-webflux</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-actuator</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
<exclusions>
<exclusion>
<groupId>org.junit.vintage</groupId>
<artifactId>junit-vintage-engine</artifactId>
</exclusion>
</exclusions>
</dependency>
<dependency>
<groupId>io.projectreactor</groupId>
<artifactId>reactor-test</artifactId>
<scope>test</scope>
</dependency>
APM Java Agent Version - 1.8.0
Elastic search - 7.2.0
APM server - 7.2.0
Exception observed -
2020-05-07 00:03:31.529 [main] INFO co.elastic.apm.agent.bci.bytebuddy.ErrorLoggingListener - org.springframework.web.context.support.GenericWebApplicationContext refers to a missing class
java.lang.IllegalStateException: Cannot resolve type description for javax.servlet.ServletContext
at co.elastic.apm.agent.shaded.bytebuddy.pool.TypePool$Resolution$Illegal.resolve(TypePool.java:159)
at co.elastic.apm.agent.shaded.bytebuddy.pool.TypePool$Default$LazyTypeDescription$TokenizedGenericType.toErasure(TypePool.java:6241)
at co.elastic.apm.agent.shaded.bytebuddy.pool.TypePool$Default$LazyTypeDescription$GenericTypeToken$Resolution$Raw$RawAnnotatedType.of(TypePool.java:3412)
at co.elastic.apm.agent.shaded.bytebuddy.pool.TypePool$Default$LazyTypeDescription$GenericTypeToken$Resolution$Raw.resolveReturnType(TypePool.java:3302)
at co.elastic.apm.agent.shaded.bytebuddy.pool.TypePool$Default$LazyTypeDescription$LazyMethodDescription.getReturnType(TypePool.java:6796)
at co.elastic.apm.agent.shaded.bytebuddy.description.method.MethodDescription$AbstractBase.asSignatureToken(MethodDescription.java:838)
at co.elastic.apm.agent.bci.bytebuddy.FailSafeDeclaredMethodsCompiler.compile(FailSafeDeclaredMethodsCompiler.java:85)
at co.elastic.apm.agent.bci.bytebuddy.FailSafeDeclaredMethodsCompiler.compile(FailSafeDeclaredMethodsCompiler.java:66)
at co.elastic.apm.agent.shaded.bytebuddy.dynamic.scaffold.MethodRegistry$Default.prepare(MethodRegistry.java:471)
at co.elastic.apm.agent.shaded.bytebuddy.dynamic.scaffold.inline.RedefinitionDynamicTypeBuilder.make(RedefinitionDynamicTypeBuilder.java:198)
at co.elastic.apm.agent.shaded.bytebuddy.agent.builder.AgentBuilder$Default$ExecutingTransformer.doTransform(AgentBuilder.java:10327)
at co.elastic.apm.agent.shaded.bytebuddy.agent.builder.AgentBuilder$Default$ExecutingTransformer.transform(AgentBuilder.java:10263)
at co.elastic.apm.agent.shaded.bytebuddy.agent.builder.AgentBuilder$Default$ExecutingTransformer.access$1600(AgentBuilder.java:10029)
at co.elastic.apm.agent.shaded.bytebuddy.agent.builder.AgentBuilder$Default$ExecutingTransformer$LegacyVmDispatcher.run(AgentBuilder.java:10648)
at co.elastic.apm.agent.shaded.bytebuddy.agent.builder.AgentBuilder$Default$ExecutingTransformer$LegacyVmDispatcher.run(AgentBuilder.java:10595)
at java.security.AccessController.doPrivileged(Native Method)
at co.elastic.apm.agent.shaded.bytebuddy.agent.builder.AgentBuilder$Default$ExecutingTransformer.transform(AgentBuilder.java:10186)
at sun.instrument.TransformerManager.transform(Unknown Source)
at sun.instrument.InstrumentationImpl.transform(Unknown Source)
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(Unknown Source)
at java.security.SecureClassLoader.defineClass(Unknown Source)
at java.net.URLClassLoader.defineClass(Unknown Source)
at java.net.URLClassLoader.access$100(Unknown Source)
at java.net.URLClassLoader$1.run(Unknown Source)
at java.net.URLClassLoader$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at org.springframework.boot.autoconfigure.condition.FilteringSpringBootCondition.resolve(FilteringSpringBootCondition.java:108)
at org.springframework.boot.autoconfigure.condition.FilteringSpringBootCondition$ClassNameFilter.isPresent(FilteringSpringBootCondition.java:140)
at org.springframework.boot.autoconfigure.condition.OnWebApplicationCondition.getOutcome(OnWebApplicationCondition.java:71)
at org.springframework.boot.autoconfigure.condition.OnWebApplicationCondition.getOutcomes(OnWebApplicationCondition.java:58)
at org.springframework.boot.autoconfigure.condition.FilteringSpringBootCondition.match(FilteringSpringBootCondition.java:49)
at org.springframework.boot.autoconfigure.AutoConfigurationImportSelector.filter(AutoConfigurationImportSelector.java:246)
at org.springframework.boot.autoconfigure.AutoConfigurationImportSelector.getAutoConfigurationEntry(AutoConfigurationImportSelector.java:121)
at org.springframework.boot.autoconfigure.AutoConfigurationImportSelector$AutoConfigurationGroup.process(AutoConfigurationImportSelector.java:396)
at org.springframework.context.annotation.ConfigurationClassParser$DeferredImportSelectorGrouping.getImports(ConfigurationClassParser.java:882)
at org.springframework.context.annotation.ConfigurationClassParser$DeferredImportSelectorGroupingHandler.processGroupImports(ConfigurationClassParser.java:808)
at org.springframework.context.annotation.ConfigurationClassParser$DeferredImportSelectorHandler.process(ConfigurationClassParser.java:779)
at org.springframework.context.annotation.ConfigurationClassParser.parse(ConfigurationClassParser.java:192)
at org.springframework.context.annotation.ConfigurationClassPostProcessor.processConfigBeanDefinitions(ConfigurationClassPostProcessor.java:319)
at org.springframework.context.annotation.ConfigurationClassPostProcessor.postProcessBeanDefinitionRegistry(ConfigurationClassPostProcessor.java:236)
at org.springframework.context.support.PostProcessorRegistrationDelegate.invokeBeanDefinitionRegistryPostProcessors(PostProcessorRegistrationDelegate.java:275)
at org.springframework.context.support.PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(PostProcessorRegistrationDelegate.java:95)
at org.springframework.context.support.AbstractApplicationContext.invokeBeanFactoryPostProcessors(AbstractApplicationContext.java:706)
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:532)
at org.springframework.boot.web.reactive.context.ReactiveWebServerApplicationContext.refresh(ReactiveWebServerApplicationContext.java:66)
at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:747)
at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:397)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:315)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1226)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1215)
at com.dhisco.hotel.search.HotelSearchApp.main(HotelSearchApp.java:14)
Could someone please suggest what I am missing ?

Answer 1

Elastic APM now supports Webflux (either Tomcat or Netty):
https://github.com/elastic/apm-agent-java/pull/1305
Since Elastic APM 1.25.0, this is enabled by setting enable_experimental_instrumentations to true, either in elasticapm.properties, or as JVM argument:
enable_experimental_instrumentations=true
Before this, it was enabled by setting disable_instrumentations to empty string:
disable_instrumentations=
https://github.com/elastic/apm-agent-java/issues/60#issuecomment-822419013
Features
Test application:
available as an executable jar and also used for unit-testing instrumentation
provides both functional and annotated controllers endpoints
executable with netty or tomcat as server, which allows to cover Webflux with or without Servlets
provides a client to call itself (based on Webflux client), thus using any third-party HTTP client is not necessary
Instrumentation:
Webflux server: covers both functional and annotated endpoints variants
Webflux client: not covered yet, see add support for Webflux client instrumentation #1306
using new plugin API and indy dispatcher.
adds reactor instrumentation for context-propagation

Answer 2

Looks like there is no support from elastic for WebFlux yet
Check here https://github.com/elastic/apm-agent-java/issues/60
They are currently working on it, but there is not a date to be ready yet

Answer 3

WebFlux can run on Servlet containers with support for the Servlet 3.1 Non-Blocking IO API as well as on other async runtimes such as Netty and Undertow.
Each Spring Boot web application includes an embedded web server.
For reactive stack applications, the spring-boot-starter-webflux includes Reactor Netty by default I guess. And it does not include Servlet API (Netty is non-Servlet runtime), but it looks like your Elastic APM expects this API to be present.
Try to use spring-boot-starter-tomcat instead of Netty. When switching to a different HTTP server, you need to exclude the default dependencies in addition to including the one you need.
Here is an example:
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-webflux</artifactId>
<exclusions>
<!-- Exclude the Netty dependency -->
<exclusion>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-reactor-netty</artifactId>
</exclusion>
</exclusions>
</dependency>
<!-- Use Tomcat instead -->
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-tomcat</artifactId>
</dependency>
Tomcat dependency brings Servlet API. Perhaps it will resolve your issue.