Sharing session over multiple servers with redis - redis

Question

I'm implementing a distributed redis cache in .NET Core to be shared among multiple .NET Core services in a microservice environment. The microservices are on multiple servers behind a load-balancer on IIS. The redis cache will be used to temporarily hold data related to individual users. The redis server will be hosted internally. I already have a cookie used for external authentication (AuthCookie), but I don't use Identity or Session as the user is expected to be logged in. I just send the AuthCookie to my authentication service, it authenticates and I fill my ClaimsPrincipal with the results.
Since my cache will be user specific, I thought it would be a good idea to utilize .Net Session with a redis distributed cache backing. I want to use AuthCookie as the key, but it fails because it doesn't know how to decrypt it, which sucks. Therefore, I have to have a second, .net session specific cookie. The problem is, the session isn't working across servers on my load balancer, even with persisting my keys. Here's a simple version of my set up:
public void ConfigureServices(IServiceCollection services)
{
var host = "127.0.0.1";
var port = "6379";
var conn = $"{host}:{port}";
var redis = ConnectionMultiplexer.Connect(conn);
services.AddDataProtection().PersistKeysToRedis(redis, "DataProtection-Keys");
services.AddDistributedRedisCache(options =>
{
options.Configuration = conn;
options.InstanceName = "master";
});
services.AddSession(options => options.CookieName = "NetSession");
services.AddMvc();
}
public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
{
app.UseSession();
app.UseMvc();
}
public class RedisController : Controller
{
public string Get(string key)
{
return HttpContext.Session.GetString(key);
}
public string Post([FromBody] CacheData data)
{
HttpContext.Session.SetString(data.Key, data.Value);
return $"Added {data.Key} with {data.Value}";
}
}
This works fine on one server, but setting 3 instances of it up on my load balancer won't work. I call the load-balancer, it sets a key on server A, redis will show as masterSOMEGUID, and a long "NetSession" cookie will be returned. I call get on the load-balancer, server B picks it up, "NetSession" is sent, but when trying to find the key it generates a different GUID and can't find it. If I hit server A again it will find it no problem. I can't figure out what I'm doing wrong.
A separate solution I've found is to not use Session and just use IDistributedCache with the AuthCookie that's already on the requests.
public class RedisController : Controller
{
private readonly IDistributedCache _cache;
public RedisController(IDistributedCache cache)
{
_cache = cache
}
public string Get(string key)
{
return _cache.GetString($"{HttpContext.Request.Cookies["NetSession"]}{key}");
}
public string Post([FromBody] CacheData data)
{
_cache.SetString($"{HttpContext.Request.Cookies["NetSession"]}{data.Key}", data.Value);
return $"Added {data.Key} with {data.Value}";
}
}
This obviously creates a lot more entries on the redis store. Is it bad form to do it this way? It should be noted that I won't be storing user details, just user responses and other reusable information.