Valkey

Cache and sessions. Not required for more than one web node — sessions in the database work across machines too — but faster for both.

Valkey is the open-source fork of Redis and speaks the same protocol, so anything written for Redis — the Drupal redis module, Laravel's redis driver, any Redis client — works against it unchanged. A stack runs one cache — Valkey, Redis or Memcached — so naming a different one replaces it.

Your application finds it at VALKEY_HOST, and at REDIS_HOST as well, since that is the name most clients look for. The port is 6379 (REDIS_PORT). See Variables.

How much memory it holds is sized from your machine: most of a cache machine when it has one to itself, a share of your plan when it sits beside your site. When it is full it evicts the least recently used key (allkeys-lru). Set VALKEY_MAXMEMORY_POLICY to noeviction for a store that must not lose keys — and remember that nothing in it is backed up.

#Versions

Pin the version, not the build: name 9.0 and the platform matches it to the current build, so a security rebuild reaches you without anybody editing a repository.

#What you can change

In vallic.yaml — what each one does is on Service settings:

services:
  - valkey:
      version: '9.0'
      environment:
        VALKEY_MAXMEMORY_POLICY: …
        VALKEY_DATABASES: …

Anything not on this list refuses the deploy, naming the variable — rather than being accepted and quietly ignored.