Spring Boot with Embedded Mongo : Cannot assign requested address: JVM_Bind - spring

Question

I am trying to setup a JUnit test for a Spring Boot with embedded Mongo & Kafka :-
#RunWith(SpringRunner.class)
#SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.NONE,
classes = {AccountingApplication.class})
#DataMongoTest
public class BaseEmbeddedTest {
#ClassRule
public static KafkaEmbedded embeddedKafka = new KafkaEmbedded(1, true);
#Autowired
private MongoTemplate mongoTemplate;
#Test
public void emptyTest(){
}
}
src/test/resources/application.yml :-
spring:
data:
mongodb:
port: 0
kafka:
bootstrap-servers: ${spring.embedded.kafka.brokers}
PROBLEM
Caused by: org.springframework.beans.BeanInstantiationException: Failed to instantiate [de.flapdoodle.embed.mongo.config.IMongodConfig]: Factory method 'embeddedMongoConfiguration' threw exception; nested exception is java.net.BindException: Cannot assign requested address: JVM_Bind
at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:189)
at org.springframework.beans.factory.support.ConstructorResolver.instantiateUsingFactoryMethod(ConstructorResolver.java:588)
... 140 more
Caused by: java.net.BindException: Cannot assign requested address: JVM_Bind
at java.net.DualStackPlainSocketImpl.bind0(Native Method)
at java.net.DualStackPlainSocketImpl.socketBind(DualStackPlainSocketImpl.java:106)
at java.net.AbstractPlainSocketImpl.bind(AbstractPlainSocketImpl.java:387)
at java.net.PlainSocketImpl.bind(PlainSocketImpl.java:190)
at java.net.ServerSocket.bind(ServerSocket.java:375)
at java.net.ServerSocket.<init>(ServerSocket.java:237)
at de.flapdoodle.embed.process.runtime.Network.getFreeServerPort(Network.java:80)
at org.springframework.boot.autoconfigure.mongo.embedded.EmbeddedMongoAutoConfiguration.embeddedMongoConfiguration(EmbeddedMongoAutoConfiguration.java:147)
What am I doing wrong here ?
Version:-
dependencyManagementPluginVersion = '1.0.3.RELEASE'
springBootVersion = '1.5.6.RELEASE'
springCloudVersion = 'Dalston.SR2'
projectVersion = '0.0.1-SNAPSHOT'
javaVersion = 1.8
kotlinVersion = '1.1.4'

Answer 1

This annotation: #DataMongoTest causes Spring Boot to create an embedded Mongo instance. The exception messages tells us that the embedded Mongo instance cannot start because there is already a process running on the port it is trying to run on.
The embedded Mongo instance is configured by EmbeddedMongoAutoConfiguration and the strategy applied by Spring Boot - for port allocation - is as follows:
if configured Mongo port > 0 then
use the configured port
else
assign a random port
end
So, I suspect that your test context is configured with a non zero value for spring.data.mongodb.port. I know you posted your application.yml which implies that you are - correctly - assigning a zero value to spring.data.mongodb.port but if you put a breakpoint inside the EmbeddedMongoAutoConfiguration constructor and peek inside the properties parameter I think you'll see that the actual value in use by that configuration class is not zero. If the port value passed to EmbeddedMongoAutoConfiguration is actually zero but you are still getting the JVM_Bind error then that implies that this call: Network.getFreeServerPort(this.getHost()) is not returning a free port and that seems unlikely.
In order to fix this issue: as long as you configure your test context with spring.data.mongodb.port=0 then the embedded Mongo instance will be assigned a random port and this random port will be made known to other aspects of your Spring context (such as your MongoTemplate) which need to talk to that Mongo instance.