To use redis for caching in magento2 I added the following part in app/etc/env.php:
'cache' => array ( 'frontend' => array ( 'default' => array ( 'backend' => 'Cm_Cache_Backend_Redis', 'backend_options' => array ( 'server' => '127.0.0.1', 'port' => '6379', 'persistent' => '', 'database' => '0', 'force_standalone' => '0', 'connect_retries' => '1', 'read_timeout' => '10', 'automatic_cleaning_factor' => '0', 'compress_data' => '1', 'compress_tags' => '1', 'compress_threshold' => '20480', 'compression_lib' => 'gzip', ), ), 'page_cache' => array ( 'backend' => 'Cm_Cache_Backend_Redis', 'backend_options' => array ( 'server' => '127.0.0.1', 'port' => '6379', 'persistent' => '', 'database' => '1', 'force_standalone' => '0', 'connect_retries' => '1', 'read_timeout' => '10', 'automatic_cleaning_factor' => '0', 'compress_data' => '0', 'compress_tags' => '1', 'compress_threshold' => '20480', 'compression_lib' => 'gzip', ), ), ), ),