dbal_service_single_master_slave_connection.xml

<?xml version="1.0" ?>

<srv:container xmlns="http://symfony.com/schema/dic/doctrine"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:srv="http://symfony.com/schema/dic/services"
    xsi:schemaLocation="http://symfony.com/schema/dic/services http://symfony.com/schema/dic/services/services-1.0.xsd
                        http://symfony.com/schema/dic/doctrine http://symfony.com/schema/dic/doctrine/doctrine-1.0.xsd">

    <config>
        <dbal dbname="mysql_db" user="mysql_user" password="mysql_s3cr3t" unix-socket="/path/to/mysqld.sock" keep-slave="true">
            <slave name="slave1" dbname="slave_db" user="slave_user" password="slave_s3cr3t" unix-socket="/path/to/mysqld_slave.sock" />
            <default-table-option name="engine">InnoDB</default-table-option>
        </dbal>
    </config>
</srv:container>