How to Fix HTTP Error 502.5 – ANCM Out-Of-Process Startup Failure

What Is HTTP Error 502.5 – ANCM Out-Of-Process Startup Failure?

So, you just deployed your ASP.NET Core app, and instead of seeing your beautiful website… You get hit with:

HTTP Error 502.5 – ANCM Out-Of-Process Startup Failure

This isn’t a server crash. It means that the ASP.NET Core Module (ANCM), which acts as a bridge between IIS and your .net Core app, tried to start your app and failed.

In simple terms: your app didn’t even get a chance to run. Something stopped it during the startup phase.

Why Does This Error Happen?

Let’s break down the most common (and human-understandable) reasons:

1. Missing .net Runtime on the Server

You built your app to run on a specific version of .net… but your server doesn’t have that version installed. Boom—error.

2. Your App Is Crashing at Startup

Maybe it works fine on your machine, but fails on the server due to configuration issues, bad connection strings, or an unhandled exception in Program.cs.

3. Wrong Hosting Model

If you’ve configured your app to use out-of-process hosting, but the server expects in-process (or vice versa), startup will fail.

4. Blocked Files

Windows might block downloaded files. It’s a security thing, but it can stop your app from running.

5. Permissions Problems

The IIS application pool identity might not have permission to access your deployed files or folders.

Step-by-Step: How to Fix HTTP Error 502.5

Step 1: Enable Logging

Modify your web.config to help yourself see what’s happening.

xml
<aspNetCore 
    processPath="dotnet" 
    arguments="YourApp.dll" 
    stdoutLogEnabled="true" 
    stdoutLogFile=".\logs\stdout" 
    hostingModel="OutOfProcess" />

Don’t forget:

• Create a logs folder in your app’s root directory
• Deploy again
• Reproduce the error
• Check the log file (e.g., stdout_12345678.log) for real clues

Step 2: Make Sure the Right .NET Runtime Is Installed

Run this command on the server:

bash
dotnet --list-runtimes

Compare the list with the version your app targets. If it’s missing, install it from Microsoft’s official .NET downloads page.

TIP: Use self-contained deployment if you don’t want to worry about runtime installs.

Step 3: Double-Check Your appsettings and Program.cs

Bad connection strings, missing environment variables, or app secrets can crash your app before it even starts.

• Use try-catch around your CreateHostBuilder() code in Program.cs to log critical startup exceptions.
• Check your appsettings.Production.json—is everything valid and complete?

Step 4: Unblock Your Files

If you copied files from another PC or downloaded from the internet:

PowerShell method:

bash
Get-ChildItem -Recurse | Unblock-File

Manual method:

• Right-click a file
• Choose “Properties”
• Click “Unblock” (if available)

Do this for all relevant .dll and config files.

Step 5: Review IIS Permissions

Make sure the application pool identity has proper read and execute access to your app’s folder.

• Right-click your site folder > Properties > Security tab
• Add IIS APPPOOL\<YourAppPoolName> with Read & Read & execute permissions

Step 6: Test Your App Locally (in Release Mode)

Sometimes it’s not the deployment—it’s the app itself.

• Publish your app in Release mode
• Run it on your local machine with:

bash
dotnet YourApp.dll

If it crashes locally in Release mode, you know the issue isn’t just on the server.

Frequently Asked Questions – ANCM 502.5 Error

Q1: What does ANCM even stand for?

ANCM = ASP.NET Core Module. It acts as a middleman between IIS and your app.

Q2: Is this a fatal error?

No, but it stops your app from running. Until you fix the cause, your site won’t load.

Q3: Can I fix this without access to IIS?

Not really. You’ll need access to logs, runtime info, and file permissions, so server access is required.

Q4: Can this happen on Azure too?

Yes. Azure App Services can also show 502.5 errors if startup fails, especially due to missing runtime or bad settings.

Q5: Can I just switch to In-Process hosting to fix it?

Not always. That depends on how your app was built and your server setup. But yes, switching between InProcess and OutOfProcess in web.config is one thing you can try during debugging.

Pro Tip: Use Self-Contained Deployment for Less Drama

When you publish with:

bash

dotnet publish -c Release -r win-x64 --self-contained

You bundle the .NET runtime with your app. That means you don’t need to worry whether the server has the right version installed.

Final Thoughts: You’ve Got This

The HTTP Error 502.5 – ANCM Out-Of-Process Startup Failure can feel intimidating, but it’s usually a simple misstep—wrong runtime, a blocked file, or a bad config.

With logging enabled and the above steps, you’ll be back online in no time.