ASP.NET 2.0 - How to use app_offline.htm

Question

I've read about the app_offline.htm file which can be placed within the root of a .NET 2.0 application which will in essence shut down the application and disable any other pages from being requested.

I've placed the file in the root, and my site still loads. I went into default documents in IIS and set it to app_offline.htm and the site still loads (this might have been a caching issue though)

Anyway, has anyone run into issues using this? Am I doing something wrong?

Answer 1

I have used the extremely handy app_offline.htm trick to shut down/update sites in the past without any issues.

Be sure that you are actually placing the "app_offline.htm" file in the "root" of the website that you have configured within IIS.

Also ensure that the file is named exactly as it should be: app_offline.htm

Other than that, there should be no other changes to IIS that you should need to make since the processing of this file (with this specific name) is handled by the ASP.NET runtime rather than IIS itself (for IIS v6).

Be aware, however, that although placing this file in the root of your site will force the application to "shut down" and display the content of the "app_offline.htm" file itself, any existing requests will still get the real website served up to them. Only new requests will get the app_offline.htm content.

If you're still having issues, try the following links for further info:

Scott Gu's App_Offline.htm

App_Offline.htm and working around the "IE Friendly Errors" feature

Will app_offline.htm stop current requests or just new requests?

Answer 2

Make sure your app_offline.htm file is at least 512 bytes long. A zero-byte app_offline.htm will have no effect.

UPDATE: Newer versions of ASP.NET/IIS may behave better than when I first wrote this.

UPDATE 2: If you are using ASP.NET MVC, add the following to web.config:

<?xml version="1.0"?>
<configuration>
    <system.webServer>
        <modules runAllManagedModulesForAllRequests="true" />
    </system.webServer>
</configuration>

Answer 3

Note that this behaves the same on IIS 6 and 7.x, and .NET 2, 3, and 4.x.

Also note that when app_offline.htm is present, IIS will return this http status code:

HTTP/1.1 503 Service Unavailable

This is all by design. This allows your load balancer (or whatever) to see that the server is off line.

Answer 4

Possible Permission Issue

I know this post is fairly old, but I ran into a similar issue and my file was spelled correctly.

I originally created the app_offline.htm file in another location and then moved it to the root of my application. Because of my setup I then had a permissions issue.

The website acted as if it was not there. Creating the file within the root directory instead of moving it, fixed my problem. (Or you could just fix the permission in properties->security)

Hope it helps someone.

Answer 5

Make sure that app_offline.htm is in the root of the virtual directory or website in IIS.

Answer 6

Make sure filename extensions are visible in explorer and filename is actually

app_offline.htm

not

app_offline.htm.htm

Answer 7

I ran into an issue very similar to the original question that took me a little while to resolve.

Just incase anyone else is working on an MVC application and finds their way into this thread, make sure that you have a wildcard mapping to the appropriate .Net aspnet_isapi.dll defined. As soon as I did this, my app_offline.htm started behaving as expected.

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IIS 6 Configuration Steps

On IIS Application Properties, select virtual Directory tab.

Under Application Settings, click the Configuration button.

Under Wildcard application maps, click the Insert button.

Enter C:\WINDOWS\Microsoft.NET\Framework64\v4.0.30319\aspnet_isapi.dll, click OK.