Mongo Configuration for Amazon DocumentDB utilizing Spring-Boot and spring-data-mongodb

MongoConfig.java

import com.mongodb.MongoClient;
import com.mongodb.MongoClientOptions;
import com.mongodb.MongoCredential;
import com.mongodb.ServerAddress;
import lombok.extern.log4j.Log4j2;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Profile;
import org.springframework.data.mongodb.config.AbstractMongoConfiguration;
import org.springframework.data.mongodb.repository.config.EnableMongoRepositories;

import javax.net.ssl.SSLContext;
import javax.net.ssl.TrustManagerFactory;
import java.io.FileInputStream;
import java.io.InputStream;
import java.security.KeyStore;
import java.security.cert.CertificateFactory;
import java.security.cert.X509Certificate;

@Configuration
@Log4j2
@EnableMongoRepositories(basePackages = "<REPOSITORIES_PACKAGE>")
public class MongoConfig extends AbstractMongoConfiguration {
    @Value("${DB_HOST}")
    private String dbUri;
    @Value("${DB_PORT}")
    private String port;
    @Value("${DB_NAME}")
    private String dbName;
    @Value("${APP_DIR}")
    private String directory;
    @Value("${DB_USER}")
    private String dbUser;
    @Value("${DB_PWD}")
    private char[] dbPassword;

    private static final String RDS_COMBINED_CA_BUNDLE = "rds-combined-ca-bundle.pem";

    @Override
    protected String getDatabaseName() {
        return db;
    }

    @Override
    public MongoClient mongoClient() {
        MongoClient mongoClient = new MongoClient(new ServerAddress(dbUri, Integer.parseInt(port)), mongoCredentials(), mongoClientOptions());
        return mongoClient;
    }

    @Bean
    public MongoClientOptions mongoClientOptions() {
        MongoClientOptions.Builder mongoClientOptions = MongoClientOptions.builder().sslInvalidHostNameAllowed(true).sslEnabled(true);
        try {
            String fileName = directory + RDS_COMBINED_CA_BUNDLE;
            InputStream is = new FileInputStream(fileName);
// You could get a resource as a stream instead.

            CertificateFactory cf = CertificateFactory.getInstance("X.509");
            X509Certificate caCert = (X509Certificate) cf.generateCertificate(is);

            TrustManagerFactory tmf = TrustManagerFactory
                    .getInstance(TrustManagerFactory.getDefaultAlgorithm());
            KeyStore ks = KeyStore.getInstance(KeyStore.getDefaultType());
            ks.load(null); // You don't need the KeyStore instance to come from a file.
            ks.setCertificateEntry("caCert", caCert);

            tmf.init(ks);

            SSLContext sslContext = SSLContext.getInstance("TLS");
            sslContext.init(null, tmf.getTrustManagers(), null);
            mongoClientOptions.sslContext(sslContext);
        } catch (Exception e) {
            log.error(e);
        }


        return mongoClientOptions.build();
    }

    private MongoCredential mongoCredentials() {
        return MongoCredential.createCredential(dbUser, dbName, dbPassword);
    }
}

What is the path for directory in your configuration, because when I am receiving "unable to find valid certification path to requested target" even though I hard coded the file path
@bean
public MongoClientOptions mongoClientOptions() {
MongoClientOptions.Builder mongoClientOptions = MongoClientOptions.builder().sslInvalidHostNameAllowed(true).sslEnabled(true);
try {
String fileName = "/src/main/resources/new-rds.pem";

        CertificateFactory cf = CertificateFactory.getInstance("X.509");
        X509Certificate caCert = (X509Certificate) cf.generateCertificate(Files.newInputStream(Paths.get(fileName)));

        TrustManagerFactory tmf = TrustManagerFactory
            .getInstance(TrustManagerFactory.getDefaultAlgorithm());
        KeyStore ks = KeyStore.getInstance(KeyStore.getDefaultType());
        ks.load(null); // You don't need the KeyStore instance to come from a file.
        ks.setCertificateEntry("caCert", caCert);

        tmf.init(ks);

        SSLContext sslContext = SSLContext.getInstance("TLS");
        sslContext.init(null, tmf.getTrustManagers(), null);
        mongoClientOptions.sslContext(sslContext);
    } catch (Exception e) {
    }
    return mongoClientOptions.build();
}

For me, I followed the java section of this page with this part:

keytool -importcert -trustcacerts -file rds-combined-ca-bundle.pem -alias rds -keystore rds-ca-certs -storepass <keystorePassword>

and in the code

        String keystore = "rds-ca-certs";
        String keystorePassword = "<keystorePassword>";

        System.setProperty("javax.net.ssl.trustStore", keystore);
        System.setProperty("javax.net.ssl.trustStorePassword", keystorePassword);

Also I downloaded the rds-ca-2019-root.pem and it is working.

Hey, have you tried accessing any HTTPS rest endpoint from the same app? I noticed if I have a https call before or after connecting to the documnetdb, all the following connections will fail with SunCertPathBuilderException.