Redis

• Source: https://github.com/redis/redis
• License: BSD-3 (v7.2 and earlier) / RSALv2 + SSPLv1 (v7.4-7.x) / tri-licensed RSALv2 / SSPLv1 / AGPLv3 (v8+, the bundled redis:alpine). For commercial hosting, select AGPLv3 or RSALv2.
• Alternatives: Valkey, Dragonfly, Memcached

In-memory database used for caching and message queuing.

To avoid network traffic/delays, run Redis on the same server as the containers that require it (one instance per server).