An example of how to use Master/Slave support with mautic. In this case supporting an optional read-only replica cluster with AuroraDB.

config_prod.php

<?php

$loader->import('config.php');

if (file_exists(__DIR__.'/security_local.php')) {
    $loader->import('security_local.php');
} else {
    $loader->import('security.php');
}

/*
$container->loadFromExtension("framework", array(
    "validation" => array(
        "cache" => "apc"
    )
));

$container->loadFromExtension("doctrine", array(
    "orm" => array(
        "metadata_cache_driver" => "apc",
        "result_cache_driver"   => "apc",
        "query_cache_driver"    => "apc"
    )
));
*/

// Read Only db cluster support.
// In future this may be best as a modification of the core config.php.
$dbHostRO = $container->hasParameter('mautic.db_host_ro') ? $container->getParameter('mautic.db_host_ro') : null;
if (!empty($dbHostRO)) {
    // Default from config.php
    $dbalSettings = [
        'driver'   => '%mautic.db_driver%',
        'host'     => '%mautic.db_host%',
        'port'     => '%mautic.db_port%',
        'dbname'   => '%mautic.db_name%',
        'user'     => '%mautic.db_user%',
        'password' => '%mautic.db_password%',
        'charset'  => 'UTF8',
        'types'    => [
            'array'    => 'Mautic\CoreBundle\Doctrine\Type\ArrayType',
            'datetime' => 'Mautic\CoreBundle\Doctrine\Type\UTCDateTimeType',
        ],
        // Prevent Doctrine from crapping out with "unsupported type" errors due to it examining all tables in the database and not just Mautic's
        'mapping_types' => [
            'enum'  => 'string',
            'point' => 'string',
            'bit'   => 'string',
        ],
        'server_version' => '%mautic.db_server_version%',
    ];

    // Add a single slave (which is a load balanced Aurora read-only cluster).
    $dbalSettings['keep_slave'] = true;
    $dbalSettings['slaves'] = [
        'slave1' => [
            'host'     => $dbHostRO,
            'port'     => '%mautic.db_port%',
            'dbname'   => '%mautic.db_name%',
            'user'     => '%mautic.db_user%',
            'password' => '%mautic.db_password%',
            'charset'  => 'UTF8',
        ]
    ];
    $container->loadFromExtension('doctrine', array(
        'dbal' => $dbalSettings
    ));
}

$debugMode = $container->hasParameter('mautic.debug') ? $container->getParameter('mautic.debug') : $container->getParameter('kernel.debug');

$container->loadFromExtension('monolog', [
    'channels' => [
        'mautic',
    ],
    'handlers' => [
        'main' => [
            'formatter'    => $debugMode ? 'mautic.monolog.fulltrace.formatter' : null,
            'type'         => 'fingers_crossed',
            'buffer_size'  => '200',
            'action_level' => ($debugMode) ? 'debug' : 'error',
            'handler'      => 'nested',
            'channels'     => [
                '!mautic',
            ],
        ],
        'nested' => [
            'type'      => 'rotating_file',
            'path'      => '%kernel.logs_dir%/%kernel.environment%.php',
            'level'     => ($debugMode) ? 'debug' : 'error',
            'max_files' => 7,
        ],
        'mautic' => [
            'formatter' => $debugMode ? 'mautic.monolog.fulltrace.formatter' : null,
            'type'      => 'rotating_file',
            'path'      => '%kernel.logs_dir%/mautic_%kernel.environment%.php',
            'level'     => ($debugMode) ? 'debug' : 'notice',
            'channels'  => [
                'mautic',
            ],
            'max_files' => 7,
        ],
    ],
]);

//Twig Configuration
$container->loadFromExtension('twig', [
    'cache'       => '%mautic.tmp_path%/%kernel.environment%/twig',
    'auto_reload' => true,
]);

// Allow overriding config without a requiring a full bundle or hacks
if (file_exists(__DIR__.'/config_override.php')) {
    $loader->import('config_override.php');
}

// Allow local settings without committing to git such as swift mailer delivery address overrides
if (file_exists(__DIR__.'/config_local.php')) {
    $loader->import('config_local.php');
}