问System.Runtime.Caching在本地工作，但在部署到web服务器时无法工作

EN

public class CacheHelper
{
    /// <summary>
    /// 
    /// </summary>
    /// <param name="key"></param>
    /// <returns></returns>
    public object GetValue(string key)
    {
        var memoryCache = MemoryCache.Default;
        return memoryCache.Get(key);
    }

    /// <summary>
    /// 
    /// </summary>
    /// <param name="key"></param>
    /// <param name="value"></param>
    /// <param name="absExpiration"></param>
    /// <returns></returns>
    public bool Add(string key, object value, DateTimeOffset absExpiration)
    {
        var memoryCache = MemoryCache.Default;
        return memoryCache.Add(key, value, absExpiration);
    }

    /// <summary>
    /// 
    /// </summary>
    /// <param name="key"></param>
    public void Delete(string key)
    {
        var memoryCache = MemoryCache.Default;
        if (memoryCache.Contains(key)) memoryCache.Remove(key);
    }
}

var cacheHelper = new CacheHelper();
var cachedValue = cacheHelper.GetValue(keyName);

cacheHelper.Add(keyName, cacheValue, DateTimeOffset.UtcNow.AddMinutes(30));