Add support for Redis server-side local cache evaluation

[shawara]

Is your feature request related to a problem?

For distributed systems each client is using a local cache which will increase the number of requests to fetch the same configs for X connected services

Describe the solution you'd like

Redis is an in-memory data structure store, used as a distributed, in-memory key–value database, cache and message broker, with optional durability.
We can use Redis caching for local evaluation instead of local memory and set the personal key token in only one service or worker to fetch the feature flags configs and save it on the Redis cache which is shared across all services.

Describe alternatives you've considered

Related sub-libraries

redis

• All of them
• posthog-web
• posthog-node
• posthog-react-native

Additional context

Thank you for your feature request – we love each and every one!

[benjackwhite]

I'm not sure that adding redis support is a good call tbh. It's another level of complexity to cover one database option which will overtime need updates, have requests for more different databases to be supported...

We could consider exposing some sort of API allowing you to control the local evaluation background refresher, so that you can set your own list of flags. Would that be helpful to the problem you are describing?

[PookMook]

we face the same problem as Shawara, the main problem not being the number of requests but more on the consistency between hosts if the polling ticks are not synced.
If we get a way to get the poller to save/read to/from an external store, that would solve our problems for sure.
That would save us from the Frankenstein solution we are starting to plan

[JCMais]

@PookMook did u guys end up implementing the Frankenstein solution?

[PookMook]

We didn't for the sake of time. If you're interested in what our solutions were I can share.

For the time being, we bailed out of posthog till there's an option to manipulate the poller. We have a bespoke solution (that we hoped to replace with posthog FF feature to let CX manage feature flag and feature releases on their own term), so we piggyback our of this for now.