Does each named cache need its own backplane?

[pdonovan]

We have a tenanted system where each tenant gets its own Fusion cache with a name and a cache key prefix. We also use Redis as L2 and as the backplane. The Redis connection string is the same for each cache, and so I have registered the Redis cache itself once with DI:

    var connectionMultiplexer = ConnectionMultiplexer.Connect(redisConnectionString);
    services.AddSingleton<IConnectionMultiplexer>(connectionMultiplexer);
    services.AddStackExchangeRedisCache(options =>
    {
        options.ConnectionMultiplexerFactory = () => Task.FromResult<IConnectionMultiplexer>(connectionMultiplexer);
    });

Note that I'm adding the IConnectionMultiplexer itself to DI so that the OpenTelemetry instrumentation can find it.

When setting up the caches, do I need to add WithBackplane(new RedisBackplane()) to each cache, or can I also use WithRegisteredBackplane() so that each named cache shares a single Redis backplane?

For each tenant I currently do the following:

var cacheBuilder = services.AddFusionCache(tenantIdentifier)
            .WithCacheKeyPrefix($"{tenantIdentifier}:")
            .WithSystemTextJsonSerializer()
            .WithRegisteredDistributedCache()
                .WithBackplane(
                    new RedisBackplane(new RedisBackplaneOptions { Configuration = "some-redis-conn-string" })
                );

Can or should I do this instead?

var cacheBuilder = services.AddFusionCache(tenantIdentifier)
            .WithCacheKeyPrefix($"{tenantIdentifier}:")
            .WithSystemTextJsonSerializer()
            .WithRegisteredDistributedCache()
            .WithRegisteredBackplane();

Looking at it now it makes sense but I couldn't find anything in the docs to confirm it. There doesn't seem to be a way to add a name or name prefix to the backplane.

[jodydonetti]

Hi @pdonovan , there's the BackplaneChannelPrefix option (see here), which is similar to the CacheKeyPrefix option, but for the backplane.

I'll take a better look at the docs and maybe update them to include it, thanks for pointing that out!

Hope this helps, let me know.

[pdonovan]

Thanks, but I'm still not sure about the crux of my question which is whether it's permissible to use a single backplane for multiple named caches.

[jodydonetti]

Ah, now I get it: not the same Redis instance, but the same RedisBackplane instance?
No, it's better not to: to save on connections you can share the same underlying IConnectionMultiplexer, but that's it.

Hope this helps.