Spring-Kafka seems to stop Spring Boot web to run correctly - spring-boot

Question

I'm trying to experiment a bit with Spring-Kafka within a Spring Boot application.
I have a very minimal configuration as shown in my application.properties
spring.kafka.consumer.bootstrap-servers=127.0.0.1:29092
spring.kafka.consumer.group-id=myGroup
And Kafka running in a container.
Now, the connection seems to work fine and I can dispatch messages, however something weird happens.
As soon as I introduce:
(it's in Kotlin)
#KafkaListener(topics = arrayOf("kotlinTestTopic"))
fun listenAsObject(#Payload data : String) {
println(data)
}
NONE of my web controllers works anymore and I get a "connection refused", as if the Spring Boot startup did not complete.
And as soon as I comment it out, the controllers are back.
Any hint on what I'm doing wrong?
EDIT
Here are the startup logs:
. ____ _ __ _ _
/\\ / ___'_ __ _ _(_)_ __ __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
\\/ ___)| |_)| | | | | || (_| | ) ) ) )
' |____| .__|_| |_|_| |_\__, | / / / /
=========|_|==============|___/=/_/_/_/
:: Spring Boot :: (v2.2.2.RELEASE)
2019-12-11 14:24:50.552 INFO 10659 --- [ main] t.g.com.testboot.TestbootApplicationKt : Starting TestbootApplicationKt on theirish-ThinkPad-L390 with PID 10659 (/home/theirish/Documenti/programming/testboot/build/classes/kotlin/main started by theirish in /home/theirish/Documenti/programming/testboot)
2019-12-11 14:24:50.554 INFO 10659 --- [ main] t.g.com.testboot.TestbootApplicationKt : No active profile set, falling back to default profiles: default
2019-12-11 14:24:50.651 WARN 10659 --- [kground-preinit] o.s.h.c.j.Jackson2ObjectMapperBuilder : For Jackson Kotlin classes support please add "com.fasterxml.jackson.module:jackson-module-kotlin" to the classpath
2019-12-11 14:24:51.031 INFO 10659 --- [ main] .s.d.r.c.RepositoryConfigurationDelegate : Bootstrapping Spring Data JPA repositories in DEFAULT mode.
2019-12-11 14:24:51.112 INFO 10659 --- [ main] .s.d.r.c.RepositoryConfigurationDelegate : Finished Spring Data repository scanning in 40ms. Found 4 JPA repository interfaces.
2019-12-11 14:24:51.476 INFO 10659 --- [ main] trationDelegate$BeanPostProcessorChecker : Bean 'org.springframework.transaction.annotation.ProxyTransactionManagementConfiguration' of type [org.springframework.transaction.annotation.ProxyTransactionManagementConfiguration] is not eligible for getting processed by all BeanPostProcessors (for example: not eligible for auto-proxying)
2019-12-11 14:24:51.680 INFO 10659 --- [ main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat initialized with port(s): 8080 (http)
2019-12-11 14:24:51.689 INFO 10659 --- [ main] o.apache.catalina.core.StandardService : Starting service [Tomcat]
2019-12-11 14:24:51.689 INFO 10659 --- [ main] org.apache.catalina.core.StandardEngine : Starting Servlet engine: [Apache Tomcat/9.0.29]
2019-12-11 14:24:51.767 INFO 10659 --- [ main] o.a.c.c.C.[Tomcat].[localhost].[/] : Initializing Spring embedded WebApplicationContext
2019-12-11 14:24:51.767 INFO 10659 --- [ main] o.s.web.context.ContextLoader : Root WebApplicationContext: initialization completed in 1172 ms
2019-12-11 14:24:51.894 INFO 10659 --- [ main] o.hibernate.jpa.internal.util.LogHelper : HHH000204: Processing PersistenceUnitInfo [name: default]
2019-12-11 14:24:51.936 INFO 10659 --- [ main] org.hibernate.Version : HHH000412: Hibernate Core {5.4.9.Final}
2019-12-11 14:24:52.065 INFO 10659 --- [ main] o.hibernate.annotations.common.Version : HCANN000001: Hibernate Commons Annotations {5.1.0.Final}
2019-12-11 14:24:52.129 INFO 10659 --- [ main] com.zaxxer.hikari.HikariDataSource : HikariPool-1 - Starting...
2019-12-11 14:24:52.235 INFO 10659 --- [ main] com.zaxxer.hikari.HikariDataSource : HikariPool-1 - Start completed.
2019-12-11 14:24:52.245 INFO 10659 --- [ main] org.hibernate.dialect.Dialect : HHH000400: Using dialect: org.hibernate.dialect.H2Dialect
2019-12-11 14:24:52.778 INFO 10659 --- [ main] o.h.e.t.j.p.i.JtaPlatformInitiator : HHH000490: Using JtaPlatform implementation: [org.hibernate.engine.transaction.jta.platform.internal.NoJtaPlatform]
2019-12-11 14:24:52.783 INFO 10659 --- [ main] j.LocalContainerEntityManagerFactoryBean : Initialized JPA EntityManagerFactory for persistence unit 'default'
2019-12-11 14:24:53.366 WARN 10659 --- [ main] JpaBaseConfiguration$JpaWebConfiguration : spring.jpa.open-in-view is enabled by default. Therefore, database queries may be performed during view rendering. Explicitly configure spring.jpa.open-in-view to disable this warning
2019-12-11 14:24:53.483 INFO 10659 --- [ main] o.s.s.concurrent.ThreadPoolTaskExecutor : Initializing ExecutorService 'applicationTaskExecutor'
2019-12-11 14:24:53.739 INFO 10659 --- [ main] o.a.k.clients.admin.AdminClientConfig : AdminClientConfig values:
bootstrap.servers = [127.0.0.1:29092]
client.dns.lookup = default
client.id =
connections.max.idle.ms = 300000
metadata.max.age.ms = 300000
metric.reporters = []
metrics.num.samples = 2
metrics.recording.level = INFO
metrics.sample.window.ms = 30000
receive.buffer.bytes = 65536
reconnect.backoff.max.ms = 1000
reconnect.backoff.ms = 50
request.timeout.ms = 120000
retries = 5
retry.backoff.ms = 100
sasl.client.callback.handler.class = null
sasl.jaas.config = null
sasl.kerberos.kinit.cmd = /usr/bin/kinit
sasl.kerberos.min.time.before.relogin = 60000
sasl.kerberos.service.name = null
sasl.kerberos.ticket.renew.jitter = 0.05
sasl.kerberos.ticket.renew.window.factor = 0.8
sasl.login.callback.handler.class = null
sasl.login.class = null
sasl.login.refresh.buffer.seconds = 300
sasl.login.refresh.min.period.seconds = 60
sasl.login.refresh.window.factor = 0.8
sasl.login.refresh.window.jitter = 0.05
sasl.mechanism = GSSAPI
security.protocol = PLAINTEXT
send.buffer.bytes = 131072
ssl.cipher.suites = null
ssl.enabled.protocols = [TLSv1.2, TLSv1.1, TLSv1]
ssl.endpoint.identification.algorithm = https
ssl.key.password = null
ssl.keymanager.algorithm = SunX509
ssl.keystore.location = null
ssl.keystore.password = null
ssl.keystore.type = JKS
ssl.protocol = TLS
ssl.provider = null
ssl.secure.random.implementation = null
ssl.trustmanager.algorithm = PKIX
ssl.truststore.location = null
ssl.truststore.password = null
ssl.truststore.type = JKS
2019-12-11 14:24:53.803 INFO 10659 --- [ main] o.a.kafka.common.utils.AppInfoParser : Kafka version: 2.3.1
2019-12-11 14:24:53.803 INFO 10659 --- [ main] o.a.kafka.common.utils.AppInfoParser : Kafka commitId: 18a913733fb71c01
2019-12-11 14:24:53.803 INFO 10659 --- [ main] o.a.kafka.common.utils.AppInfoParser : Kafka startTimeMs: 1576070693802

Answer 1

I feel incredibly dumb now.
Apparently, during my experiments, I introduced the wrong Kafka port in the Spring-Kafka configuration. As a side effect, the whole Spring Boot application hung, which is quite unexpected...