asp.net core 2.1 HTTP Error 502.5

Although it was already answered, I'll post here my solution for the same problem (HTTP Error 502.5 when starting my webapp on Asp.NET CORE 2.1, error code 0x80004005) that has a different reason, as reference of another possibility.

Short Answer:

If the name of the application has a space (character) on it, the current version of Visual Studio (15.8.9) has a bug, that doesn't include quotes to make it a literal string argument on the moment of execution (through commandline) on the web.config file, generated when publishing your webapp.

Example:

web.config generated by Visual Studio (version 15.8.9 - Date: 2018-Nov-05):

[...]
<aspNetCore processPath="dotnet" arguments=".\My Web App.dll" stdoutLogEnabled=... />
[...]

web.config with correct quotation:

[...]
<aspNetCore processPath="dotnet" arguments='".\My Web App.dll"' stdoutLogEnabled=... />
[...]

You can see on the attribute arguments on the second example, that I included (manually) single quotes, making it pass the full string ".\My Web App.dll" as the argument on the moment of execution.

Detailed Answer:

Every time I update my Visual Studio for a newer SDK (and using the most recent version of Asp.net Core in my application) it give me the Http Error 502.5, IF i do not update the runtime libraries on my server too. So, obviously the first thing that I did was update the runtime libraries on the server (which always solved this problem to me), but this time it didn't worked.

So, starting to troubleshoot, I just tried to start my webapp from the command line (prompt), and it started perfectly.

So, I knew that there was something wrong with the way my webapp was being started. The starting configuration (on asp.net core) is in the web.config file.

[...]
<aspNetCore processPath="dotnet" arguments=".\My Web App.dll" stdoutLogEnabled="false" stdoutLogFile=".\logs\stdout" />
[...]

In Asp.net Core, the web application is started/executed from the commandline (prompt) on windows, by IIS (i'm strictly speaking of common scenario).

Till now, it always had a .exe file between the published files, that started the whole thing, and this was the file called by IIS Module through commandline.

Since Asp.net CORE 2.1 (and some minor update that i don't know exactly), there is no .exe file, and the PATH of Web App is passed by argument. So you have the command that is dotnet and a argument to this command that is specified as argument attribute, on the web.config file. (as shown in the example above)

Taking a look on my published web.config file, you can see the processPath and arguments attributes. In the previous test, I knew that dotnet was a recognized command, since I was able to start my webapp on windows command prompt. Then, looking carefully the arguments attribute, I saw that there was no (surrounding) quotation for the value, that contained space characters in it.

So in the startup of my webapp, instead the dotnet command receive the full path .\My Web App.dll, it was receiving 3 different arguments: .\My , Web , App.dll .

Since the value of the arguments attribute is passed through commandline, it has to have quotation when passed to the commandline, becoming a literal string.

So I mannualy added the necessary surrounding quotation on the arguments attribute value, in the web.config file, and my web app started to work perfectly!

To see the example of the bug, and how to correct it, just take a look on the "Short Answer" examples.

Other useful information (for Asp.net Core 2.0 and up, with Windows / IIS):

If you had a web application that was working, and is not anymore, giving the error 502.5:

It's probably a versioning problem of the runtime libraries. Your webapp is asking for newer asp.net core libraries, and your server doesn't have them yet. Just update the runtime libraries on your server, and it should solve the problem. Download it from Microsoft (for the current version which is Asp.net Core 2.1, you can download from this link: https://www.microsoft.com/net/download/dotnet-core/2.1).

How to start your webapp manually, for better troubleshooting:

Open the windows command prompt, and try to execute the command dotnet. If it's not recognized, than you have to install (or repair) the asp.net core module and dependencies (google is your friend. Just search how to install asp.net core). Alternatively, you can check the Asp.net Core runtime libraries version with the command dotnet --version.

Once the dotnet command is recognized, you can start your webapp manually. Navigate to the folder where is your webapp files (usually will be in inetpub, wwwroot, etc..). Then, locate the .dll file that is your application's assembly. Usually, it will have the name of your application (pretty easy, right!?). Then, execute it with the command dotnet ".\My Web App.dll".

Example:

If there is a error, you will see some useful information on the prompt window. If the webapp starts correctly, then it's some issue with the startup configuration, probably web.config file.

Another method to see more detailed information on asp.net core failure:

https://docs.microsoft.com/en-us/aspnet/core/host-and-deploy/iis/troubleshoot?view=aspnetcore-2.1#application-event-log

Access the Application Event Log:

1. Open the Start menu, search for Event Viewer, and then select the Event Viewer app.
2. In Event Viewer, open the Windows Logs node.
3. Select Application to open the Application Event Log.
4. Search for errors associated with the failing app. Errors have a value of IIS AspNetCore Module or IIS Express AspNetCore Module in the Source column.

Details of my issue:

When executing requests, the error presented was: HTTP Error 502.5 - Process Failure.

Looking on the Events Viewer (Windows Server), the information was: "Application ' ... My Web App' with physical root 'C:\ ... \ ... \' failed to start process with commandline 'dotnet .\My Web App.dll', ErrorCode = '0x80004005 : 1."

So my error code was: 0x80004005 , and the subcode was 1.

Hope it helps somebody :)