$parameters = [
   // masters
    'localhost:7000?alias=master', 
    'localhost:7001?alias=master', 
    'localhost:7002?alias=master', 

    // slaves
    'localhost:7003', 
    'localhost:7004', 
    'localhost:7005', 
]

$options    = ['cluster' => 'redis', 'replication' => true];
           
$client = new Predis\Client($parameters, $options);

- Locals at /Users/Shared/dev/php/toters-api/vendor/predis/predis/src/Client.php:138

 ▾ $connection = (Predis\Connection\Aggregate\MasterSlaveReplication [6])
  \
   ▸ $connection->strategy = (Predis\Replication\ReplicationStrategy [3])
   |
   ⬦ $connection->master = (null)
   |
   ▾ $connection->slaves = (array [6])
    \
     ▸ $connection->slaves['slave-localhost?alias=master:7000'] = (Predis\Connection\StreamConnection [4])
     |
     ▸ $connection->slaves['slave-localhost?alias=master:7001'] = (Predis\Connection\StreamConnection [4])
     |
     ▸ $connection->slaves['slave-localhost?alias=master:7002'] = (Predis\Connection\StreamConnection [4])
     |
     ▸ $connection->slaves['slave-localhost:7003'] = (Predis\Connection\StreamConnection [4])
     |
     ▸ $connection->slaves['slave-localhost:7004'] = (Predis\Connection\StreamConnection [4])
     |
     ▸ $connection->slaves['slave-localhost:7005'] = (Predis\Connection\StreamConnection [4])
    /
   ⬦ $connection->current = (null)
   |
   ⬦ $connection->autoDiscovery = (bool) 0
   |
   ⬦ $connection->connectionFactory = (null)
  /
 ⬦ $initializer = (uninitialized)
 |
 ▾ $options = (Predis\Configuration\Options [3])
  \
   ▸ $options->input = (array [1])
   |
   ▸ $options->options = (array [2])
   |
   ▸ $options->handlers = (array [6])
  /
 ▾ $parameters = (array [6])
  \
   ▸ $parameters[0] = (array [4])
   |
   ▸ $parameters[1] = (array [4])
   |
   ▸ $parameters[2] = (array [4])
   |
   ▸ $parameters[3] = (array [4])
   |
   ▸ $parameters[4] = (array [4])
   |
   ▸ $parameters[5] = (array [4])
  /
 ▾ $replication = (Predis\Connection\Aggregate\MasterSlaveReplication [6])
  \
   ▸ $replication->strategy = (Predis\Replication\ReplicationStrategy [3])
   |
   ⬦ $replication->master = (null)
   |
   ▸ $replication->slaves = (array [6])
   |
   ⬦ $replication->current = (null)
   |
   ⬦ $replication->autoDiscovery = (bool) 0
   |
   ⬦ $replication->connectionFactory = (null)
  /
 ▾ $this = (Predis\Client [3])
  \
   ⬦ $this->connection = (null)
   |
   ▸ $this->options = (Predis\Configuration\Options [3])
   |
   ⬦ $this->profile = (null)
  /

    'redis' => [

        'clustered' => [
            'client' => 'predis',
            'cluster' => true,
            'options' => [ 'cluster' => 'redis',
                           'replication' => true 
                         ],
            'clusters' => [
                        // masters
                        [
                            'host' => env('REDIS_SHARD_1_HOST', '127.0.01'),
                            'password' => env('REDIS_PASSWORD', null),
                            'port' => env('REDIS_SHARD_1_PORT', 6379),
                            'database' => 0,
                        ],
                        [
                            'host' => env('REDIS_SHARD_2_HOST', '127.0.01'),
                            'password' => env('REDIS_PASSWORD', null),
                            'port' => env('REDIS_SHARD_2_PORT', 6379),
                            'database' => 0,
                        ],
                        [
                            'host' => env('REDIS_SHARD_3_HOST', '127.0.01'),
                            'password' => env('REDIS_PASSWORD', null),
                            'port' => env('REDIS_SHARD_3_PORT', 6379),
                            'database' => 0,
                        ],
                        // slaves (replicas)
                        [
                            'host' => env('REDIS_SHARD_1_HOST_REPLICA', '127.0.01'),
                            'password' => env('REDIS_PASSWORD', null),
                            'port' => env('REDIS_SHARD_1_PORT_REPLICA', 6379),
                            'database' => 0,
                        ],
                        [
                            'host' => env('REDIS_SHARD_2_HOST_REPLICA', '127.0.01'),
                            'password' => env('REDIS_PASSWORD', null),
                            'port' => env('REDIS_SHARD_2_PORT_REPLICA', 6379),
                            'database' => 0,
                        ],
                        [
                            'host' => env('REDIS_SHARD_3_HOST_REPLICA', '127.0.01'),
                            'password' => env('REDIS_PASSWORD', null),
                            'port' => env('REDIS_SHARD_3_PORT_REPLICA', 6379),
                            'database' => 0,
                        ]
            ],
        ], 

        'default' => [
            'host' => env('REDIS_HOST', '127.0.0.1'),
            'password' => env('REDIS_PASSWORD', null),
            'port'     => 6379,
            'database' => 0,
            'cluster' => false,
        ],
    ]

REDIS_SHARD_1_HOST=localhost?alias=master
REDIS_SHARD_2_HOST=localhost?alias=master
REDIS_SHARD_3_HOST=localhost?alias=master

REDIS_SHARD_1_HOST_REPLICA=localhost
REDIS_SHARD_2_HOST_REPLICA=localhost
REDIS_SHARD_3_HOST_REPLICA=localhost

REDIS_SHARD_1_PORT=7000
REDIS_SHARD_2_PORT=7001
REDIS_SHARD_3_PORT=7002

REDIS_SHARD_1_PORT_REPLICA=7003
REDIS_SHARD_2_PORT_REPLICA=7004
REDIS_SHARD_3_PORT_REPLICA=7005