sudo apt update
sudo apt install mariadb-server

CREATE DATABASE db_name DEFAULT CHARACTER SET utf8 COLLATE utf8_general_ci;

//user 생성
//% 로 설정하면 외부에서도 접근 가능
create user 'username'@'%' identified by 'password';

//해당 계정에 전체 권한이 열림
grant all privileges on {database}.* to 'username'@'%';
flush privileges;

//replication에 대한 권한만 설정하려면 이렇게
//위와 같이 {database}.*를 하면 예외가 발생함
//ERROR 1221 (HY000): Incorrect usage of DB GRANT and GLOBAL PRIVILEGES
grant replication slave on *.* to 'username'@'%';
flush privileges;

sudo service mysqld restart

//user 생성
//% 로 설정하면 외부에서도 접근 가능
create user 'username'@'%' identified by 'password';

sudo service mysqld restart

CHANGE MASTER TO MASTER_HOST='{master_db_ip}', 
MASTER_PORT={master_db_port}, 
MASTER_USER='{master_db_user_name}', 
MASTER_PASSWORD='{master_db_user_password}', 
MASTER_LOG_FILE='{master_db_file}', 
MASTER_LOG_POS={master_db_position};

start slave;

//\G 라고 입력하면 이쁘게 출력이 된다
show slave status\G;

// 1
@EnableAutoConfiguration(exclude = DataSourceAutoConfiguration.class)
@Configuration
public class DataSourceConfig {

	  // 2
    private final JpaProperties jpaProperties;

    public DataSourceConfig(JpaProperties jpaProperties) {
        this.jpaProperties = jpaProperties;
    }

    // 3
    @Bean
    public DataSource dataSource() {
        return new LazyConnectionDataSourceProxy(routingDataSource());
    }

    // 4
    @Bean
    public DataSource routingDataSource() {
        DataSource masterDataSource = masterDatasource();
        RoutingDataSource routingDataSource = new RoutingDataSource();
        routingDataSource.setDefaultTargetDataSource(masterDataSource);

        Map<Object, Object> dataSources = Map.of(
                "master", masterDataSource,
                "slave", slaveDatasource()
        );
        routingDataSource.setTargetDataSources(dataSources);
        return routingDataSource;
    }

    // 4
    @Bean
    @ConfigurationProperties(prefix = "datasource.master")
    public DataSource masterDatasource() {
        return DataSourceBuilder.create()
                .type(HikariDataSource.class)
                .build();
    }

    // 4
    @Bean
    @ConfigurationProperties(prefix = "datasource.slave")
    public DataSource slaveDatasource() {
        return DataSourceBuilder.create()
                .type(HikariDataSource.class)
                .build();
    }

    // 5
    @Bean
    public LocalContainerEntityManagerFactoryBean entityManagerFactory() {
        HibernateProperties hibernateProperties = new HibernateProperties();
        final Map<String, Object> properties = hibernateProperties.determineHibernateProperties(
                jpaProperties.getProperties(), new HibernateSettings()
        );
        HibernateJpaVendorAdapter hibernateJpaVendorAdapter = new HibernateJpaVendorAdapter();
        final EntityManagerFactoryBuilder entityManagerFactoryBuilder = new EntityManagerFactoryBuilder(hibernateJpaVendorAdapter, properties, null);
        return entityManagerFactoryBuilder
                .dataSource(dataSource())
                .packages("com.study.playground.replication")
                .build();
    }

    // 6
    @Bean
    public PlatformTransactionManager transactionManager(EntityManagerFactory entityManagerFactory) {
        return new JpaTransactionManager(entityManagerFactory);
    }

}

// 4
public class RoutingDataSource extends AbstractRoutingDataSource {

    private static final Logger log = LoggerFactory.getLogger(RoutingDataSource.class);

    @Override
    protected Object determineCurrentLookupKey() {
        if (TransactionSynchronizationManager.isCurrentTransactionReadOnly()) {
            log.info("current db slave");
            return "slave";
        }
        log.info("current db master");
        return "master";
    }
}

@SpringBootTest
@AutoConfigureTestDatabase(replace = AutoConfigureTestDatabase.Replace.NONE) //datasource 자동연결을 막아준다.
public class ReplicationTest {

    @Autowired
    private UserRepository userRepository;

    private User user;

    @BeforeEach
    void setUp() {
        user = new User("oz", 500);
    }

    @Test
    @DisplayName("save를 하면 master db에 데이터를 insert 한다.")
    void insert() {
        // given
        Logger logger = (Logger) LoggerFactory.getLogger(RoutingDataSource.class);
        ListAppender<ILoggingEvent> listAppender = new ListAppender<>();
        logger.addAppender(listAppender);
        listAppender.start();

        // when
        userRepository.save(user);

        // then
        final List<ILoggingEvent> list = listAppender.list;
        assertThat(list).hasSize(1);
        assertThat(list)
                .extracting(ILoggingEvent::getFormattedMessage)
                .anyMatch(log -> log.equals("current db master"));
    }

    @Test
    @DisplayName("find를 하면 slave db의 데이터를 select 한다.")
    void find() {
        // given
        userRepository.save(user);

        Logger logger = (Logger) LoggerFactory.getLogger(RoutingDataSource.class);
        ListAppender<ILoggingEvent> listAppender = new ListAppender<>();
        logger.addAppender(listAppender);
        listAppender.start();

        // when
        User findUser = userRepository.findById(user.getId())
                .orElseThrow(IllegalStateException::new);

        // then
        final List<ILoggingEvent> list = listAppender.list;
        assertThat(list).hasSize(1);
        assertThat(list)
                .extracting(ILoggingEvent::getFormattedMessage)
                .anyMatch(log -> log.equals("current db slave"));
        assertThat(findUser).isEqualTo(user);
    }

}