IIS 7 and Above
Application Request Routing (ARR)
Could ARR cause my site return a blank page with 0 errors whatsoever?
Last post Dec 10, 2019 06:37 AM by Yuk Ding
Dec 08, 2019 09:32 AM|Simon Mourier|LINK
I've been working with IIS for more than 20 years but never seen that.
I have a strange problem in a Windows Azure App Service. It's a very standard ASP.NET site that works fine 99% of the time.
But sometimes, when I connect to a specific .aspx page, I just get back a
blank page. When I say a blank page, I've check with network tools, and it's just an HTTP 200 return (with the usual headers) with zero body (no HTML, no nothing).
Other pages work fine, static files work fine. I can see the incoming request in Azure log stream, and I have zero error from the application (I log all errors). So I can't even determine what are the condition that drive the site to this blank page issue.
If I restart the web app, everything works fine again, and it can work fine during days.
I've noticed that Azure seems to be using ARR (I see ARR headers in the logs).
Could ARR or URL Rewriting cause that type of issue? What should I check and/or look into?
Dec 08, 2019 08:30 PM|lextm|LINK
First you should keep in mind there is no 100% reliability.
Second in Azure's scenarios troubleshooting such can be impossible, as you don't have access to most parts of the infrastructure (ARR for example, here).
So if you do have a way to reproduce this empty page, and do have business need to resolve it, contact Azure support, https://azure.microsoft.com/en-us/support/options/
Dec 08, 2019 10:25 PM|Simon Mourier|LINK
I know I can contact Azure support but the problem is I can't reproduce this error on will.
And when it happens, I can't let my site with the problem active either. I never saw that problem on development machine (or any other site I worked with in my whole life with IIS...)
I'm seriously thinking about migrating from Azure to an environment I can understand.
Dec 08, 2019 11:56 PM|Rovastar|LINK
I too don't do anything on Azure so it could be anything.
normal things to check if you get a blank page are did it load everything. eg if the css didn't load then the page can be blank.
I would compare the size of the page in bytes sent in the logs to other successful attempts to the "broken" one.
Add failed request tracing to the page it see what happens when it happens again.
Dec 09, 2019 07:05 AM|Yuk Ding|LINK
If you can't reproduce this issue then it would be hard even involving azure app service team. This issue sounds just like the request get completed before ARR get real response body.
So have you monitored how often is this issue happen? Besides, did you feel any special performance issue when you face this issue? Have you log the time that you face this issue and then check what happened in IIS or ARR at the that time?
Dec 09, 2019 08:57 AM|Simon Mourier|LINK
Well, the problem is there's no real problem from a server standpoint. The returned page is just empty. In fact, there is no "page" as such since the HTTP response body length (from any browser, from multiple places, and from multiple incoming host names)
is zero bytes.
Like i said, static files work fines (for example the favicon.ico works fine). It behaves like the request doesn't get to the ASP.NET handler (.aspx), like some infrastructure component just bails out and return nothing.
I was asking this question here in this forum because it looks like Azure is using ARR in some way. I'm not super familiar with ARR, and because that's basically a component I don't manage myself in this Azure hosted scenario, I was just asking if there's
a possibility that ARR (or URL Rewriting or ?) returns an empty page if misconfigured, or in certain conditions (heavy load, who knows)?
This problems happens like 1 or 2 times per week, and actually, it's possible that my site has some performance issues at boot time (for some other reason). Could that cause ARR failures? It looks like some components outside of my reach decides to stop
communicating with ASP.NET handler.
Dec 10, 2019 06:37 AM|Yuk Ding|LINK
So far we haven't meet anyone else report that ARR will remove response body and cause 0 content-length. So I can't say that this is an ARR issue.
Since it is impossible to reach the back end server of azure app service, we can't even check httperr log.
It is not sure whether boot time would cause blank page until we can always reproduce this issue.
So if we need to find the root cause, we have to monitor the performance and find a way to always reproduce this issue.
Or you can make some change to your app service randomly and monitor whether it will happen again. If any configuration would fix this issue, we may backward reasoning the root cause.