Azure中的VirtualPathProvider在发布时不工作

我创建了一个VirtualPathProvider，允许根据Request.Host移动自定义文件夹中的所有资源，用一个web应用程序管理多个域。

在我的本地机器上，MVC应用程序可以工作，当我发布到Azure时，我得到了一个不清楚的错误(HTTP 503(，我不明白我必须检查什么才能获得更多信息。

这里实现的提供者：

public class PerSiteVirtualPathProvider : VirtualPathProvider
{
    private readonly IDictionary<string, string> domainToPath;
    public PerSiteVirtualPathProvider(IDictionary<string, string> domainToPath)
    {
        this.domainToPath = domainToPath;
    }
    public override bool FileExists(string virtualPath)
    {
        return base.FileExists(virtualPath) || PerSiteFileExists(virtualPath);
    }
    public override bool DirectoryExists(string virtualDir)
    {
        return base.DirectoryExists(virtualDir) || PerSiteFileExists(virtualDir);
    }
    public override string GetFileHash(string virtualPath, IEnumerable virtualPathDependencies)
    {
        if (PerSiteFileExists(virtualPath))
        {
            var host = HttpContext.Current.Request.Url.Host.ToLower();
            return string.Concat(host, "/", virtualPath);
        }
        return base.GetFileHash(virtualPath, virtualPathDependencies);
    }
    public override VirtualFile GetFile(string virtualPath)
    {
        if (PerSiteFileExists(virtualPath))
        {
            var physicalPath = CombinePath(virtualPath);
            return new PhysicalVirtualFile(virtualPath, physicalPath);
        }
        return base.GetFile(virtualPath);
    }
    public override CacheDependency GetCacheDependency(string virtualPath, IEnumerable virtualPathDependencies, DateTime utcStart)
    {
        if (PerSiteFileExists(virtualPath))
        {
            var host = HttpContext.Current.Request.Url.Host.ToLower();
            return new CacheDependency(new[] { CombinePath(virtualPath) }, new[] { host });
        }
        return Previous.GetCacheDependency(virtualPath, virtualPathDependencies, utcStart);
    }
    private string CombinePath(string virtualPath)
    {
        var host = HttpContext.Current.Request.Url.Host.ToLower();
        var cleanVirtualPath = virtualPath.TrimStart('~', '/').Replace('/', '''');
        if (!domainToPath.ContainsKey(host))
        {
            throw new InvalidOperationException(string.Format("The specified '{0} domain is not registered.", host));
        }
        var domainFolder = domainToPath[host];
        var path = Path.Combine(domainFolder, cleanVirtualPath);
        return path;
    }
    private bool PerSiteFileExists(string virtualPath)
    {
        var path = CombinePath(virtualPath);
        var fileExists = File.Exists(path);
        return fileExists;
    }
}