Drupal backend cache memcache OR redis.

settings.cache.php

<?php

# KO memcache: http://cgit.drupalcode.org/memcache/tree/README.txt?h=8.x-2.x
//$settings['memcache']['servers'] = ['memcached:11211' => 'default'];
//$settings['memcache']['bins'] = ['default' => 'default'];
//$settings['memcache']['key_prefix'] = '';
/**
 * Memcache Configuration.
 */
/*
$settings['memcache'] = [
  'servers' => [
    'memcached:11211' => 'default',
  ],
  'bins' => [
    'default' => 'default',
  ],
  'key_prefix' => '',
];
$settings['cache']['default'] = 'cache.backend.memcache';
$settings['cache']['bins']['render'] = 'cache.backend.memcache';
*/

# OK http://cgit.drupalcode.org/redis/tree/README.md
/**
 * Redis Configuration.
 */
$settings['redis.connection']['interface'] = 'PhpRedis'; // Can be "Predis".
$settings['redis.connection']['host'] = 'redis';  // Your Redis instance hostname.
$settings['redis.connection']['port'] = '6379';  // Redis port
# Use for all bins otherwise specified.
$settings['cache']['default'] = 'cache.backend.redis';
# Use this to only use it for specific cache bins.
$settings['cache']['bins']['render'] = 'cache.backend.redis';

/*
// Custom enabled/disabled redis cache.
$conf['custom_redis_cache_enabled'] = TRUE;
if (isset($conf['custom_redis_cache_enabled']) && $conf['custom_redis_cache_enabled']) {
  $settings['redis.connection']['interface'] = 'PhpRedis'; // Can be "Predis".
  $settings['redis.connection']['host'] = 'redis';  // Your Redis instance hostname.
  $settings['redis.connection']['port'] = '6379';  // Redis port
  # Use for all bins otherwise specified.
  $settings['cache']['default'] = 'cache.backend.redis';
  # Use this to only use it for specific cache bins.
  $settings['cache']['bins']['render'] = 'cache.backend.redis';
  // Note that unlike memcached, redis persists cache items to disk so we can
  // actually store cache_class_cache_form in the default cache.
  $conf['cache_class_cache'] = 'Redis_Cache';
}
*/