How can I configure multiple(more than two) data sources in my spring boot application in MySQL and MariaDB,

Question

I have to connect to multiple data sources at runtime in a spring boot application with amazon RDS deployed MySQL and MariaDB instances respectively. For now, both are MariaDB instances residing separately. I have used the usual spring boot configurations like here Multiple data source and schema creation in Spring Boot

I am facing a problem here and that is I am not able to connect to the secondary data source where as I am able to connect to the primary data source. Here are some code snippets.

Also, I want to know any mechanism to fall back to other database instances of the same schemas at runtime if the original ones are down without affecting the application or restarting it. I have no idea about that.

import com.zaxxer.hikari.HikariDataSource;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.boot.autoconfigure.jdbc.DataSourceProperties;
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.boot.orm.jpa.EntityManagerFactoryBuilder;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Primary;
import org.springframework.data.jpa.repository.config.EnableJpaRepositories;
import org.springframework.orm.jpa.JpaTransactionManager;
import org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean;
import org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter;
import org.springframework.transaction.PlatformTransactionManager;
import org.springframework.transaction.annotation.EnableTransactionManagement;

import javax.sql.DataSource;
import java.util.HashMap;

@Configuration
@EnableTransactionManagement
@EnableJpaRepositories(basePackages = "a.b.c.d.e",
        entityManagerFactoryRef = "aEntityManagerFactory",
        transactionManagerRef = "aTransactionManager"
)
public class aConfiguration {
    @Bean
    @Primary
    @ConfigurationProperties("app.datasource.a")
    public DataSourceProperties aDataSourceProperties() {
        return new DataSourceProperties();
    }

    @Bean
    @Primary
    @ConfigurationProperties("app.datasource.a.configuration")
    public DataSource aDataSource() {
        return aDataSourceProperties().initializeDataSourceBuilder()
                .type(HikariDataSource.class).build();
    }

    @Bean
    public EntityManagerFactoryBuilder entityManagerFactoryBuilder() {
        return new EntityManagerFactoryBuilder(new HibernateJpaVendorAdapter(), new HashMap<>(), null);
    }

    @Primary
    @Bean(name = "aEntityManagerFactory")
    public LocalContainerEntityManagerFactoryBean aEntityManagerFactory(EntityManagerFactoryBuilder builder) {
        return builder
                .dataSource(aDataSource())
                .packages(SomeQualifiedEntity.class)
                .build();
    }

    @Primary
    @Bean
    public PlatformTransactionManager aTransactionManager(
            final @Qualifier("aEntityManagerFactory") LocalContainerEntityManagerFactoryBean aEntityManagerFactory) {
        return new JpaTransactionManager(aEntityManagerFactory.getObject());
    }
}

import com.zaxxer.hikari.HikariDataSource;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.boot.autoconfigure.jdbc.DataSourceProperties;
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.boot.orm.jpa.EntityManagerFactoryBuilder;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Primary;
import org.springframework.data.jpa.repository.config.EnableJpaRepositories;
import org.springframework.orm.jpa.JpaTransactionManager;
import org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean;
import org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter;
import org.springframework.transaction.PlatformTransactionManager;
import org.springframework.transaction.annotation.EnableTransactionManagement;

import javax.sql.DataSource;
import java.util.HashMap;

@Configuration
@EnableTransactionManagement
@EnableJpaRepositories(basePackages = "u.v.w.x.y",
        entityManagerFactoryRef = "bEntityManagerFactory",
        transactionManagerRef = "bTransactionManager"
)
public class aConfiguration {
    @Bean
    @Primary
    @ConfigurationProperties("app.datasource.b")
    public DataSourceProperties bDataSourceProperties() {
        return new DataSourceProperties();
    }

    @Bean
    @Primary
    @ConfigurationProperties("app.datasource.b.configuration")
    public DataSource bDataSource() {
        return bDataSourceProperties().initializeDataSourceBuilder()
                .type(HikariDataSource.class).build();
    }

    @Bean
    public EntityManagerFactoryBuilder entityManagerFactoryBuilder() {
        return new EntityManagerFactoryBuilder(new HibernateJpaVendorAdapter(), new HashMap<>(), null);
    }

    @Primary
    @Bean(name = "bEntityManagerFactory")
    public LocalContainerEntityManagerFactoryBean bEntityManagerFactory(EntityManagerFactoryBuilder builder) {
        return builder
                .dataSource(bDataSource())
                .packages(SomeQualifiedEntity.class)
                .build();
    }

    @Primary
    @Bean
    public PlatformTransactionManager bTransactionManager(
            final @Qualifier("bEntityManagerFactory") LocalContainerEntityManagerFactoryBean bEntityManagerFactory) {
        return new JpaTransactionManager(aEntityManagerFactory.getObject());
    }
}

app.datasource.a.url=
app.datasource.a.username=
app.datasource.a.password=
app.datasource.a.driverClassName=org.mariadb.jdbc.Driver

app.datasource.b.url=
app.datasource.b.username=
app.datasource.b.password=
app.datasource.b.driverClassName=org.mariadb.jdbc.Driver

I wish I could provide the entities and the repositories, but I can't. Sorry for that.

Answer 1

I configured my database / datasource in spring in the application.properties file. Although I just had one DB, I tried it with multiple out of curiosity and it worked. So maybe try it there? The format is as such:

spring.h2.console.enabled=true
spring.datasource.url=jdbc:h2:mem:testdb
spring.data.jpa.repositories.bootstrap-mode=default