# services.yaml
services:
     _defaults:
        autowire: true      # Automatically injects dependencies in your services.
        autoconfigure: true
    my_cache.chain:
        class: Symfony\Component\Cache\Adapter\ChainAdapter
        arguments:
            - [ '@cache.adapter.array', '@cache.adapter.redis' ]
        tags:
            - { name: cache.pool, namespace: 'my-custom-ns' }

# cache.yaml
framework:
    cache:
        pools:
            my_chain_pool:
                adapter: my_cache.chain

# services.yaml
services:
    my_redis.adapter:
        parent: 'cache.adapter.redis'
        tags:
            - { name: cache.pool, namespace: 'my-custom-ns' }

# cache.yaml
framework:
    cache:
        pools:
            my_chain_pool:
                adapters: [cache.adapter.array, my_redis.adapter]