MongoClient doesn't read from secondary server

Question

I'm trying to use a cluster of documentDB on AWS. On this cluster, I have 2 instances, one primary for writeOps and one secondary for readOps...

If I create the connection with connectionString like this:

String host = getHost();
Integer port = Integer.parseInt(getPort());
String[] arrCredentials = getCredentials();
String credentials = String.format("%s:%s", arrCredentials[0], arrCredentials[1]);
String database = getDatabase();
String options = "ssl=true&replicaSet=rs0&readPreference=secondaryPreferred";
    
String connection = String.format("mongodb://%s@%s:%d/%s?%s", 
                        credentials, host, port, database, options);
return MongoClients.create(new ConnectionString(connection));

It works well, and the readOps are served by the secondary instance...

But, when I try to use MongoClients.create() this way:

public MongoClient mongoClient() {
    return MongoClients.create(MongoClientSettings.builder()
            .applyToClusterSettings(settings ->
                    settings
                         .hosts(singletonList(new ServerAddress(
                                    getHost(), Integer.parseInt(getPort()))))
                         .requiredReplicaSetName("rs0")
                         .requiredClusterType(ClusterType.REPLICA_SET)
            )
            .applyToSslSettings(setting ->
                    setting.enabled(true)
            )
            .readPreference(ReadPreference.secondaryPreferred())
            .credential(getCredential())
            .build());
}

All calls, readOps and writeOps, are served by the primary instance.

Answer 1

I found it!!!

When you create the MongoClienteSettings with ConnectionString, the value of ClusterMode is automaticly setted to MULTIPLE. That doesn't occur with Builder...

So, to get the same behavour with MongoClientSetting.Builder(), you need to set it. Like this:

public MongoClient mongoClient() {
    return MongoClients.create(MongoClientSettings.builder()
            .applyToClusterSettings(settings ->
                    settings
                         .hosts(singletonList(new ServerAddress(
                                    getHost(), Integer.parseInt(getPort()))))
                         .requiredReplicaSetName("rs0")
                         .requiredClusterType(ClusterType.REPLICA_SET)
                         .mode(ClusterConnectionMode.MULTIPLE))
            )
            .applyToSslSettings(setting ->
                    setting.enabled(true)
            )
            .readPreference(ReadPreference.secondaryPreferred())
            .credential(getCredential())
            .build());
}

Now it's working well :)

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