Multiple types of Distributed Cache in ASP.NET Core

Question

Suppose I have a ASP.NET Core 2.x application.

I would like to use Redis for standard IDistributedCache dependency injection, but use SQL Server Distributed cache as the backing for Session middleware.

Is this possible? If so, how would you go about configuring this in Startup.cs?

Henk Mollema · Accepted Answer · 2018-08-28 09:06:30Z

1

The distributed session state storage injects the IDistributedCache instance by default. This means you should configure the SQL Server distributed cache as the default one if you would like to use that for session state.

For your own caching purposes, you could create a "wrapper interface" which specifically represents the Redis cache (such as IRedisCache), register it and inject that in your middleware/controllers/services. For example:

public interface IRedisDistributedCache : IDistributedCache
{
}

public void ConfigureServices(IServiceCollection services)
{
    // Add Redis caching
    services.AddDistributedRedisCache();
    services.AddSingleton<IRedisDistributedCache, RedisCache>();

    // Add SQL Server caching as the default cache mechanism
    services.AddDistributedSqlServerCache();
}

public class FooController : Controller
{
    private readonly IRedisDistributedCache _redisCache;

    public FooController(IRedisDistributedCache redisCache)
    {
        _redisCache = redisCache;
    }
}

answered Aug 28, 2018 at 9:06

Henk Mollema

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6 Comments

user1142433 Over a year ago

How would you initialize the Redis instance in this case? Normally, I've initialized it in services.AddDistributedRedisCache() call.

Henk Mollema Over a year ago

@user1142433 see the code example. I'm calling AddDistributedRedisCache() just like you normally would, and afer that bind RedisCache implemenation to the IRedisDistributedCache "wrapper interface".

user1142433 Over a year ago

So you're adding two IDistributedCache cache items to the DI service (one Redis and one SQL based)? And when Session calls for an IDistributedCache implementation it gets the SQL version because you added it to the service config after the Redis version? In other words, how does the service resolver decide which IDistributedCache it gives to the Service middleware?

Henk Mollema Over a year ago

@user1142433 that's correct. The container will pick the last one you registered.

user1142433 Over a year ago

I see now how it should work in principle. Unfortunately, the sample won't compile because "There is no implicit conversion from RedisCache to IRedisDistributedCache" on line services.AddSingleton<IRedisDistributedCache, RedisCache> ();

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