When deploying an ASP.NET Core application to IIS, you may find IIS returning HTTP Error 502.5 instead of your web page.
I recently hit this problem after manually modifying the
web.config file. Fortunately, the problem is easy to fix.
In this post, we see what needs to be in
web.config for ASP.NET Core, explain why the error occurs, and show how to fix it.
ASP.NET Core Web Config
In ASP.NET Core applications, the
web.config file contains a handler that directs requests to the
AspNetCoreModule and an
aspNetCore element that defines and configures the ASP.NET Core process to execute your web application.
Here is a minimal
web.config file for an ASP.NET Core application:
<?xml version="1.0" encoding="utf-8"?> <configuration> <system.webServer> <handlers> <add name="aspNetCore" path="*" verb="*" modules="AspNetCoreModule" resourceType="Unspecified" /> </handlers> <aspNetCore processPath="%LAUNCHER_PATH%" arguments="%LAUNCHER_ARGS%" stdoutLogEnabled="true" stdoutLogFile=".\logs\stdout" forwardWindowsAuthToken="false"/> </system.webServer> </configuration>
Note that it's possible that you don't have a
web.config file in your ASP.NET Core project. If you do not, one will be generated for you when publishing the project, as IIS and IIS Express require a
web.config file when hosting an ASP.NET Core web app.
Why do I get the error?
HTTP Error 502.5 - Bad Gateway and
HTTP Error 502.5 - Process Failure error messages occur in ASP.NET Core when IIS fails to execute the
One common reason for this to occur on a previously working web application is when you deploy an untransformed
web.config file, such as the file shown above.
web.config contains the variables
%LAUNCHER_ARGS% rather than the correct paths. When IIS tries to run ASP.NET Core, it uses
%LAUNCHER_ARGS% rather than the correct path and arguments.
How do I fix the error?
To fix the HTTP Error 502.5 in ASP.NET Core, you need to transform the
web.config and replace the untransformed
web.config file on the IIS web server.
This transformation takes place when you choose to
publish your web application. The transformed
web.config ends up in the published output folder. Therefore, you simply need to
publish your web application and copy the resulting
web.config file onto the server.
In a transformed
web.config file, the
aspNetCore element will look something like this:
<aspNetCore processPath="dotnet" arguments=".\MyApplication.dll" stdoutLogEnabled="true" stdoutLogFile=".\logs\stdout" forwardWindowsAuthToken="false" />
%LAUNCHER_PATH% has been replaced by
%LAUNCHER_ARGS% has been replaced by the path to the main web application dll