Redis Setup with Drupal 9

Here are Steps for configured Redis in Drupal 9 / Drupal 8 Project .

1) First I download Redis module for a Drupal 9 environment and stored it in 'modules/contrib' directory and enabled the same.

2) For the working of Redis module we need its libraries, so first you have to download the phpredis php extension library from https://github.com/nicolasff/phpredis. Extract the entire contents of the archive into the 'libraries/' folder.

3) If setup on local machine XAMPP then first configured redis on locally and configured php.ini : extension=redis and check phpinfo()

4) Ones Redis setup, After that update the settings.php file with the following code:

$settings['redis.connection']['interface'] = 'PhpRedis';
    // Host ip address.
    $settings['redis.connection']['host']      = '127.0.0.1';
    $settings['cache']['default'] = 'cache.backend.redis';
    // Redis port.
    $settings['redis.connection']['port']      = '6379';
    $settings['redis.connection']['base']      = 12;
    // Password of redis updated in php.ini file.
    $settings['redis.connection']['password'] = "password";
    $settings['cache']['bins']['bootstrap'] = 'cache.backend.chainedfast';
    $settings['cache']['bins']['discovery'] = 'cache.backend.chainedfast';
    $settings['cache']['bins']['config'] = 'cache.backend.chainedfast';

5) Create services.yml inisde default folder and add the below code in it.

services:
  # Cache tag checksum backend. Used by redis and most other cache backend
  # to deal with cache tag invalidations.
  cache_tags.invalidator.checksum:
   class: Drupal\redis\Cache\RedisCacheTagsChecksum
   arguments: ['@redis.factory']
   tags:
     - { name: cache_tags_invalidator }

  # Replaces the default lock backend with a redis implementation.
  lock:
    class: Drupal\Core\Lock\LockBackendInterface
    factory: ['@redis.lock.factory', get]

  # Replaces the default persistent lock backend with a redis implementation.
  lock.persistent:
    class: Drupal\Core\Lock\LockBackendInterface
    factory: ['@redis.lock.factory', get]
    arguments: [true]

  # Replaces the default flood backend with a redis implementation.
  flood:
    class: Drupal\Core\Flood\FloodInterface
    factory: ['@redis.flood.factory', get]

Hope this is useful.