Between this non-compete clause of their license:
> You may not make the functionality of the Software or a Modified version available to third parties as a service or distribute the Software or a Modified version in a manner that makes the functionality of the Software available to third parties.
..and this clarification in their FAQ:
> A “competitive offering” is a product that is sold to third parties, including through paid support arrangements, that is derived from the Redis’ code-base and significantly overlaps the capabilities of a Redis commercial product. For example, this definition would include hosting or embedding Redis as part of a solution that is sold competitively against our commercial versions of Redis (either Redis Enterprise Software or Redis Cloud).
It’s pretty clear that any SaaS product simply using Redis as a dependency for a completely different product (e.g. Discourse) is in the clear. But it would be nice if they could spell that out as an unaffected use case.