ASP.NET Core: Failed to start application '/LM/W3SVC/####/ROOT', ErrorCode '0x8007023e'.

You gotta love .NET core compilation errors! They provide the most ambiguous error messages known to man. I have noticed the error message and accompanying error code could be caused by a multitude of factors. This error is no different so I’ll make my contribution, hoping this may help someone else.

The error in question occurred really randomly whilst deploying a minor HTML update to a .NET Core site I was hosting within an Azure Web App. It couldn’t have been a simpler release - change to some markup in a View. When the site loaded, I was greeted with the following error:

Failed to start application '/LM/W3SVC/####/ROOT', ErrorCode '0x8007023e’.

I was able to get some further information about the error from the Event Log:

Application 'D:\home\site\wwwroot\' failed to start. Exception message:
Executable was not found at 'D:\home\site\wwwroot\%LAUNCHER_PATH%.exe'
Process Id: 10848.
File Version: 13.1.19331.0. Description: IIS ASP.NET Core Module V2.

The error could only be reproduced on Azure and not within my local development and staging environments. I created a new deployment slot to check if somehow my existing slot got corrupted. Unfortunately, this made no difference. The strange this is, the application was working completely fine up until this release. It's still unknown to me what could have happened for this error to occur all of a sudden.

Solution

It would seem that no one else on the planet experienced this issue when Googling the error message and error code. After a lot of fumbling around, the fix ended up being relatively straight-forward. The detail provided by the Event Log pointed me in the right direction and the clue was in the %LAUNCHER_PATH% placeholder. The %LAUNCHER_PATH% placeholder is set in the web.config and this is normally replaced when the application is run in Visual Studio or IIS.

In Azure, both %LAUNCHER_PATH% and %LAUNCHER_ARGS% variables need to be explicitly set. The following line in the web.config needs to be changed from:

<aspNetCore processPath="%LAUNCHER_PATH%" arguments="%LAUNCHER_ARGS%" stdoutLogEnabled="false" stdoutLogFile=".\logs\stdout" forwardWindowsAuthToken="false" startupTimeLimit="3600" requestTimeout="23:00:00" hostingModel="InProcess">

To:

<aspNetCore processPath=".\Site.Web.exe" arguments="" stdoutLogEnabled="false" stdoutLogFile=".\logs\stdout" forwardWindowsAuthToken="false" startupTimeLimit="3600" requestTimeout="23:00:00" hostingModel="InProcess">

The processPath is now pointing to the executable generated by the project. In this case, "Site.Web.exe". Also, since no arguments are being parsed in my build, the arguments attribute is left empty. When you push up your next release, the error should be rectified.

As a side note, there was one thing recommended to me by Azure support regarding my publish settings in Visual Studio. It was recommended that I should set the deployment mode from "Framework-Dependent" to "Self-Contained". This will ensure the application will always run in its current framework version on the off-chance framework changes happen at an Azure level.