Generate a static html error page from umbraco dynamic one to make it more resilient

ErrorPageGeneratorEventHandlers.cs

public class ErrorPageGeneratorEventHandlers : ApplicationEventHandler
{
    private static readonly object Lock = new object();

    protected override void ApplicationStarted(UmbracoApplicationBase umbracoApplication,
        ApplicationContext applicationContext)
    {
        GenerateStaticErrorPage();

        ContentService.Published += (sender, args) => GenerateStaticErrorPage();
        ContentService.UnPublished += (sender, args) => GenerateStaticErrorPage();
    }

    private static async void GenerateStaticErrorPage()
    {
        var errorPage = UmbracoHelpers.GetAllNodesOfType<PageError>().FirstOrDefault();
        if (errorPage == null)
        {
            return;
        }
        var errorPageAbsoluteUrl = errorPage.UrlAbsolute();

        await GenerateStaticErrorPage(errorPageAbsoluteUrl);
    }

    private static async Task GenerateStaticErrorPage(string errorPageAbsoluteUrl)
    {
        try
        {
            var httpClient = new HttpClient();
            var httpResponseMessage = await httpClient.GetAsync(errorPageAbsoluteUrl);
            if (httpResponseMessage.StatusCode != HttpStatusCode.OK)
            {
                return;
            }
            var errorPageHtml = await httpResponseMessage.Content.ReadAsStringAsync();
            var path = AppDomain.CurrentDomain.BaseDirectory
                       + "error.html";

            using (var streamWriter = new StreamWriter(path))
            {
                lock (Lock)
                {
                    streamWriter.Write(errorPageHtml);
                }
            }
        }
        catch (Exception e)
        {
            LogHelper.Error(
                typeof(ErrorPageGeneratorEventHandlers),
                "Could write error page to file", e);
        }
    }
}

can you explain more?

Yes please explain in detail what is going on through the code. Thanks

This event handler download a page error type as anything is published or unpublished, fetches it with an http client and saves it as "error.html". This way your editors can have a page that they edit the content for, all menus updates just like the rest of your site, but is more resilient than a dynamic page (something needs to be very broken for iis not to be able to server a static html file).