'cache' =>
  array (
    'frontend' =>
    array (
      'default' =>
      array (
        'backend' => 'Cm_Cache_Backend_Redis',
        'backend_options' =>
        array (
          'server' => 'magento2-redis-sentinel', // A load-balanced host where my sentinel service resides.
          'sentinel_master' => 'mymaster',
          'sentinel_master_verify' => '1',
          'port' => '26379',
          'database' => '1',
          'compress_data' => 0,
        ),
      ),
      'page_cache' =>
      array (
        'backend' => 'Cm_Cache_Backend_Redis',
        'backend_options' =>
        array (
          'server' => 'magento2-redis-sentinel',
          'sentinel_master' => 'mymaster',
          'sentinel_master_verify' => '1',
          'port' => '26379',
          'database' => '2',
          'compress_data' => 0,
        ),
      ),
    ),
  ),

Unable to connect to a redis sentinel: Unknown sentinel subcommand 'setClientTimeout'