How to create a dynamic datasource using SpringBoot

Spring has dynamic datasource routing if that's where you are headed. In my case it is the same schema (WR/RO)

public class RoutingDataSource extends AbstractRoutingDataSource {

  @Autowired
  private DataSourceConfig dataSourceConfig;

  @Override
  protected Object determineCurrentLookupKey() {
    return DbContextHolder.getDbType();
  }

  public enum DbType {
    MASTER, WRITE, READONLY,  
  }

Then you need a custom annotation and an aspect

@Target({ElementType.METHOD, ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
public @interface ReadOnlyConnection {
}

@Aspect 
@Component
@Order(1)
public class ReadOnlyConnectionInterceptor {

  Pointcut(value = "execution(public * *(..))")
  public void anyPublicMethod() {}

  @Around("@annotation(readOnlyConnection)")
  public Object proceed(ProceedingJoinPoint proceedingJoinPoint, ReadOnlyConnection readOnlyConnection) throws Throwable           {
    Object result = null;
    try {
      DbContextHolder.setDbType(DbType.READONLY);
      result = proceedingJoinPoint.proceed();
      DbContextHolder.clearDbType();
      return result;
    } finally {
      DbContextHolder.clearDbType();
    }
  }
}

And then you can act on you DB with the tag @ReadOnlyConnection

@Override
@Transactional(readOnly = true)
@ReadOnlyConnection
public UnitDTO getUnitById(Long id) {
  return unitRepository.findOne(id);
}

An example can be found here: https://github.com/afedulov/routing-data-source.

I used that as a basis for my work although it is still in progress because I still need to resolve runtime dependencies ( i.e. hibernate sharding ).