Why does the MongoDB Java driver try to connect to localhost?

Working with Data Drivers
1 
 private MongoClientSettings getTotalSettings() {
        return MongoClientSettings.builder()
                .applicationName(APPLICATION_NAME)
                .applyToClusterSettings(builder -> builder.applySettings(getClusterSettings()))
                .applyToConnectionPoolSettings(builder -> builder.applySettings(getConnectionPoolSettings()))
                .credential(getMongoCredential())
                .build();
    }

    private ClusterSettings getClusterSettings() {
        return ClusterSettings.builder()
                .hosts(Collections.singletonList(new ServerAddress(TEST_HOST, PORT)))
                .build();
    }

// etc....

TEST_HOST is the url of aws ec2.

I didn’t set it to connect to localhost.

But when I run this project locally I get the following log:

2023-06-13 15:09:37.975 INFO 96205 — [ restartedMain] org.mongodb.driver.client : MongoClient with metadata {“driver”: {“name”: “mongo-java-driver|sync”, “version”: “4.6.1”}, “os”: {“type”: “Darwin”, “name”: “Mac OS X”, “architecture”: “aarch64”, “version”: “13.3.1”}, “platform”: “Java/Oracle Corporation/11.0.16.1+1-LTS-1”, “application”: {“name”: “temp”}} created with settings MongoClientSettings{readPreference=primary, writeConcern=WriteConcern{w=null, wTimeout=null ms, journal=null}, retryWrites=true, retryReads=true, readConcern=ReadConcern{level=null}, credential=MongoCredential{mechanism=null, userName=‘spring’, source=‘test_location_db’, password=, mechanismProperties=}, streamFactoryFactory=null, commandListeners=, codecRegistry=ProvidersCodecRegistry{codecProviders=[ValueCodecProvider{}, BsonValueCodecProvider{}, DBRefCodecProvider{}, DBObjectCodecProvider{}, DocumentCodecProvider{}, IterableCodecProvider{}, MapCodecProvider{}, GeoJsonCodecProvider{}, GridFSFileCodecProvider{}, Jsr310CodecProvider{}, JsonObjectCodecProvider{}, BsonCodecProvider{}, EnumCodecProvider{}, com.mongodb.Jep395RecordCodecProvider@5860267a]}, clusterSettings={hosts=[AWS_ADDRESS:27017], srvServiceName=mongodb, mode=SINGLE, requiredClusterType=UNKNOWN, requiredReplicaSetName=‘null’, serverSelector=‘null’, clusterListeners=‘’, serverSelectionTimeout=‘30000 ms’, localThreshold=‘30000 ms’}, socketSettings=SocketSettings{connectTimeoutMS=10000, readTimeoutMS=0, receiveBufferSize=0, sendBufferSize=0}, heartbeatSocketSettings=SocketSettings{connectTimeoutMS=10000, readTimeoutMS=10000, receiveBufferSize=0, sendBufferSize=0}, connectionPoolSettings=ConnectionPoolSettings{maxSize=500, minSize=0, maxWaitTimeMS=5000, maxConnectionLifeTimeMS=1800000, maxConnectionIdleTimeMS=600000, maintenanceInitialDelayMS=0, maintenanceFrequencyMS=60000, connectionPoolListeners=, maxConnecting=2}, serverSettings=ServerSettings{heartbeatFrequencyMS=10000, minHeartbeatFrequencyMS=500, serverListeners=‘’, serverMonitorListeners=‘’}, sslSettings=SslSettings{enabled=false, invalidHostNameAllowed=false, context=null}, applicationName=‘temp’, compressorList=, uuidRepresentation=UNSPECIFIED, serverApi=null, autoEncryptionSettings=null, contextProvider=null}
2023-06-13 15:09:38.000 INFO 96205 — [onaws.com:27017] org.mongodb.driver.connection : Opened connection [connectionId{localValue:2, serverValue:639}] to AWS_ADDRESS:27017
2023-06-13 15:09:38.000 INFO 96205 — [onaws.com:27017] org.mongodb.driver.connection : Opened connection [connectionId{localValue:1, serverValue:640}] to AWS_ADDRESS:27017
2023-06-13 15:09:38.001 INFO 96205 — [onaws.com:27017] org.mongodb.driver.cluster : Monitor thread successfully connected to server with description ServerDescription{address=AWS_ADDRESS:27017, type=STANDALONE, state=CONNECTED, ok=true, minWireVersion=0, maxWireVersion=17, maxDocumentSize=16777216, logicalSessionTimeoutMinutes=30, roundTripTimeNanos=19193083}
2023-06-13 15:09:38.187 INFO 96205 — [ restartedMain] org.mongodb.driver.client : MongoClient with metadata {“driver”: {“name”: “mongo-java-driver|sync|spring-boot”, “version”: “4.6.1”}, “os”: {“type”: “Darwin”, “name”: “Mac OS X”, “architecture”: “aarch64”, “version”: “13.3.1”}, “platform”: “Java/Oracle Corporation/11.0.16.1+1-LTS-1”} created with settings MongoClientSettings{readPreference=primary, writeConcern=WriteConcern{w=null, wTimeout=null ms, journal=null}, retryWrites=true, retryReads=true, readConcern=ReadConcern{level=null}, credential=null, streamFactoryFactory=null, commandListeners=, codecRegistry=ProvidersCodecRegistry{codecProviders=[ValueCodecProvider{}, BsonValueCodecProvider{}, DBRefCodecProvider{}, DBObjectCodecProvider{}, DocumentCodecProvider{}, IterableCodecProvider{}, MapCodecProvider{}, GeoJsonCodecProvider{}, GridFSFileCodecProvider{}, Jsr310CodecProvider{}, JsonObjectCodecProvider{}, BsonCodecProvider{}, EnumCodecProvider{}, com.mongodb.Jep395RecordCodecProvider@5860267a]}, clusterSettings={hosts=[localhost:27017], srvServiceName=mongodb, mode=SINGLE, requiredClusterType=UNKNOWN, requiredReplicaSetName=‘null’, serverSelector=‘null’, clusterListeners=‘’, serverSelectionTimeout=‘30000 ms’, localThreshold=‘30000 ms’}, socketSettings=SocketSettings{connectTimeoutMS=10000, readTimeoutMS=0, receiveBufferSize=0, sendBufferSize=0}, heartbeatSocketSettings=SocketSettings{connectTimeoutMS=10000, readTimeoutMS=10000, receiveBufferSize=0, sendBufferSize=0}, connectionPoolSettings=ConnectionPoolSettings{maxSize=100, minSize=0, maxWaitTimeMS=120000, maxConnectionLifeTimeMS=0, maxConnectionIdleTimeMS=0, maintenanceInitialDelayMS=0, maintenanceFrequencyMS=60000, connectionPoolListeners=, maxConnecting=2}, serverSettings=ServerSettings{heartbeatFrequencyMS=10000, minHeartbeatFrequencyMS=500, serverListeners=‘’, serverMonitorListeners=‘’}, sslSettings=SslSettings{enabled=false, invalidHostNameAllowed=false, context=null}, applicationName=‘null’, compressorList=, uuidRepresentation=JAVA_LEGACY, serverApi=null, autoEncryptionSettings=null, contextProvider=null}
2023-06-13 15:09:38.191 INFO 96205 — [localhost:27017] org.mongodb.driver.cluster : Exception in monitor thread while connecting to server localhost:27017

com.mongodb.MongoSocketOpenException: Exception opening socket
at com.mongodb.internal.connection.SocketStream.open(SocketStream.java:70) ~[mongodb-driver-core-4.6.1.jar:na]
at com.mongodb.internal.connection.InternalStreamConnection.open(InternalStreamConnection.java:180) ~[mongodb-driver-core-4.6.1.jar:na]
at com.mongodb.internal.connection.DefaultServerMonitor$ServerMonitorRunnable.lookupServerDescription(DefaultServerMonitor.java:193) ~[mongodb-driver-core-4.6.1.jar:na]
at com.mongodb.internal.connection.DefaultServerMonitor$ServerMonitorRunnable.run(DefaultServerMonitor.java:157) ~[mongodb-driver-core-4.6.1.jar:na]
at java.base/java.lang.Thread.run(Thread.java:834) ~[na:na]
Caused by: java.net.ConnectException: Connection refused (Connection refused)
at java.base/java.net.PlainSocketImpl.socketConnect(Native Method) ~[na:na]
at java.base/java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:412) ~[na:na]
at java.base/java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:255) ~[na:na]
at java.base/java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:237) ~[na:na]
at java.base/java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392) ~[na:na]
at java.base/java.net.Socket.connect(Socket.java:608) ~[na:na]
at com.mongodb.internal.connection.SocketStreamHelper.initialize(SocketStreamHelper.java:107) ~[mongodb-driver-core-4.6.1.jar:na]
at com.mongodb.internal.connection.SocketStream.initializeSocket(SocketStream.java:79) ~[mongodb-driver-core-4.6.1.jar:na]
at com.mongodb.internal.connection.SocketStream.open(SocketStream.java:65) ~[mongodb-driver-core-4.6.1.jar:na]
… 4 common frames omitted

why does the mongoDB java driver try to connect to localhost?

3

Hello @gantodagee_N_A ,

From my limited experiments, I was able to see what you saw if I didn’t set TEST_HOST correctly. Could you confirm that the TEST_HOST address is setup correctly? Please refer Connection Guide for Java. The reason is, I believe there is a fallback mechanism MongoAutoConfiguration.

Spring Boot has a feature called “auto configuration”. It could be that the MongoAutoConfiguration is activated with default values, which point to localhost:27017. If you don’t want that behaviour, you can either configure the properties for MongoDB (see Spring Boot Reference Documentation for valid property keys) or disable the MongoAutoConfiguration:

@SpringBootApplication(exclude = {MongoAutoConfiguration.class, MongoDataAutoConfiguration.class})

Additionally, are you following any connection guide or tutorial to work on this? If yes, then can you share the same?

Regards,
Tarun

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