What's the correct FusionCache configuration for this scenario? (No expiration + distributed invalidation)

[FrancescoBonizzi]

Hi! Imagine this scenario:

• You have n web server
• Each web server caches a key value pair collection called FeatureFlags
• Those values never changes until a person changes it manually from a secret back office, for example he could change the value of the feature flag IsFeatureXyEnabled
• The distributed cache is configured and active

Ideally I'd like that:

• On each web server the local layer caches the value forever (options => options.SetDuration(TimeSpan.MaxValue)) which currently throws), since the value can be changed only manually and I'd like the value to be refreshed only when I'm sure it is changed.
• When the man changes and saves the feature flag from the secret backoffice, the distributed cache invalidates that value, and all the web server get notified and refresh its value.

How do you configuration this scenario with FusionCache?

[jodydonetti]

Hi @FrancescoBonizzi and thanks for using FusionCache!

Yes, you can achieve what you are describing 🎉
But no, not with the distributed cache.

You see, a cache layer (both memory and distributed) is "passive" whereas you need something "active", meaning that each node gets to be notified of the change, right?
Well you are in luck: that is exactly the job of another component, the backplane.
Basically you just need to enable the backplane and... that's it: when you'll change a piece of data, a notification will be sent to all the connected nodes.
You can even enable/disable backplane notifications per-call, with a very granular control.

Currently the only current implementation available is the one for Redis, but any implementation of the IFusionCacheBackplane interface would work.

Please take a look at the docs I just linked, and tell me if you need anything else.

[FrancescoBonizzi]

Thanks a lot, for the very useful library and for your answer. Good night XD

[jodydonetti]

No problem, hope this helped!

Let me know if you have any trouble using it, and if you'll be able to achieve what you are trying to do.

ps: just to be clear, when I said "not with the distributed cache", I meant that to have the notifications you need to use the backplane, and not that you cannot use the distributed cache too (in conjunction with the backplane): you can use them both together. Just wanted to clarify this.

[FrancescoBonizzi]

I read the link you posted and it's absolutely clear. I understood, tomorrow I will implement it with my solution, I'm going to start with Redis on Azure with the distributed cache too since you suggest it's less fragile.