doctrine:
  dbal:
    default_connection: default
    connections:
      default:
        driver:   "%database_driver%"
        host:     "%database_host%"
        port:     "%database_port%"
        dbname:   "%database_name%"
        user:     "%database_user%"
        password: "%database_password%"
        charset:  UTF8
      customer:
        driver:   "%database_driver2%"
        host:     "%database_host2%"
        port:     "%database_port2%"
        dbname:   "%database_name2%"
        user:     "%database_user2%"
        password: "%database_password2%"
        charset:  UTF8

@ConfigurationProperties
public class DatabaseProperties {

    private Connection primaryConnection;

    private Connection backupConnection;

    // getter, setter ...

    public static class Connection {

        private String host;

        // getter, setter ...

    }

}

@ConfigurationProperties
public class DatabaseProperties {

    @NestedConfigurationProperty
    private Connection primaryConnection; // Connection is defined somewhere else

    @NestedConfigurationProperty
    private Connection backupConnection;

    // getter, setter ...

}