How to use Azure Cache for Redis in a .NET Core web app

If you need a distributed cache and are planning on deploying your .NET Core web app to Azure, using Azure Cache for Redis as your cache provider is a good choice.

The steps below show you how to get started…

Create an Azure Cache for Redis instance using the portal

Search for ‘azure cache for redis’ on the portal and on the create screen fill in details such as resource group, DNS name, location and cache type.

Choose the same location as whatever app will be consuming your cache to minimise latency. When you’re just getting setup I’d recommend choosing the Basic C0 cache as this is the cheapest and you can always upgrade later. For all the other tabs just accept the defaults for the moment.

Create a new Redis cache in the portal

After Azure has finished creating your new cache, navigate into it and go to the Access keys page as shown below.

Copy the primary connection string somewhere as you’ll need to put this into your appsettings.json file in the next step.

Viewing Azure Redis access keys

Setup and configure your app

Install Microsoft.Extensions.Caching.StackExchangeRedis from NuGet.

Amend Startup.cs…

Amend startup.cs to use caching

Add a connection string pointing to your Redis instance on Azure into your appsettings.json file. Remember you can get this from the Access keys page as shown above. In our real apps we’d likely store this value in Azure Key Vault.

appsetting-redis-cache

Create a cache wrapper or helper class

At this stage your app should be able to set and read items in Azure Redis by instantiating a concrete instance of the IDistributedCache instance. The next step is to create a simple thin wrapper around this interface. It’s not 100% needed but it helps keep code that is using the cache a little bit neater.

Since .NET Core 3.0 Microsofts default JSON deserializer has been System.Text.Json, however it doesn’t support circular references so in the below example I’ve fallen back to using Newtonsoft.

Note… according to Microsoft System.Text.Json will support circular references from .NET 6.0.

Cache wrapper

Inject IDistributedCache into your controller or service class

Since dependency injection is built into .NET Core and because we’ve registered the Redis Cache service in our Startup.cs file we can inject an instance of the IDistributedCache into our controller class…

Inject IDistributedCache

Check the cache when retrieving data

Finally to use the cache when getting data… we can implement the cache-aside pattern. In this pattern we…

First check the cache for a particular key.
If it does not exist we read data from the DB and store it in the cache.
If it does exist in cache we use the cached version of the data.

Below I’m checking the cache for a list of products…

Example of cache-aside pattern

In this case I’ve not set any DistributedCacheEntryOptions meaning items will not expire. If you need to set absolute or sliding expirations on items you can set the relevant options when adding them to the cache.

Remove items from cache after they’ve been updated

When some data change occurs which means previously cached items are now stale we can remove items from the cache as below…

Invalidate items in cache by removing them

In this case the list of products I previously cached is no longer valid as I’ve deleted one of them.

Depending on the situation we might not have to explicitly remove certain items from the cache like above. In many cases some staleness is acceptable so in this case we might set a sliding expiration of 1 hour or depending on the data just re-cache certain items overnight.

How to test your app is storing items in and reading from Azure Cache for Redis

To confirm everything is working as expected we can run the monitor command in the Redis console direct on the Azure portal.

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