---
source_url: https://itmustbecode.com/azure-function-isolated-worker-avoid-comments-in-the-host-file/
title: Azure Function Isolated Worker : Avoid comments in the Host file
date: 2024-12-16T21:01:31+00:00
categories:
  - blog
tags:
  - .net
  - azure-function
  - isolated-worker
word_count: 1025
reading_time_minutes: 5
type: posts
---

As a .NET developer, the yearly release cycle is always one of my most anticipated event. This years edition is no exception, as it brings **.NET 9** to the forefront with its load of improvements. However, it also marks the **end of support** for **.NET 6**, meaning it's time to think about upgrade and migration plan.

{{< figure src="./image-2.png" alt="" caption="" >}}

Over time, I’ve developed and continue to maintain a several of **Azure Functions** projects built on . **NET 6** using the **In-Process** model. With .NET 6 reaching its end of life and the **In-Process** model being slowly deprecated ([End of life Nov 2026](https://azure.microsoft.com/en-us/updates?id=retirement-support-for-the-inprocess-model-for-net-apps-in-azure-functions-ends-10-november-2026)), I decided it was the perfect timing to upgrade my projects to a newer .NET version, but also to make the switch to the **Isolated Worker** model.

During the process I encountered a **nasty** bug on **Http-triggered** functions, here's how I uncovered and resolved the issue.

## **🤒The symptoms**

I chose to upgrade my projects to **.NET 8 Isolated worker** mode. The migration path from **In-Process** to **Isolated** worker model is well documented ( _see link below_) and I was able to adjust the code and Azure infrastructure without too much problems.

> 🔗 [Migrate .NET function apps from](https://learn.microsoft.com/en-us/azure/azure-functions/migrate-dotnet-to-isolated-model?tabs=net8) [t](https://learn.microsoft.com/en-us/azure/azure-functions/migrate-dotnet-to-isolated-model?WT.mc_id=DX-MVP-5004959&tabs=net8) [he in-process model to the isolated worker model \| Microsoft Learn](https://learn.microsoft.com/en-us/azure/azure-functions/migrate-dotnet-to-isolated-model?tabs=net8)

As I began to test my new and improved functions, most of them worked on first attempt —Service Bus triggers, Timer triggers, Durable Functions all performed as expected. Unfortunately that was not the case for my **HTTP-triggered** functions.

For an unknown reason I kept receiving a **500 Internal server error** with logs indicating some kind of timeout error. The same behavior was observed whether I ran the function **locally** or deployed in **Azure**.

The most frustrating part was that if I spun up a new project in Isolated Mode and created an **HTTP-triggered** function from scratch, it worked perfectly fine without any issues.

After a couple of hours of going around in circles and loosing what's left of my hair, I stumbled upon this comment in an issue on the Azure Functions GitHub repo. The moment I read it, I knew I had found the culprit.

{{< figure src="./image-21.png" alt="" caption="" >}}

🔗 [Migrating azure functions to .net8 isolated, function hangs when triggered · Issue #2425 · Azure/Azure-Functions](https://github.com/Azure/Azure-Functions/issues/2425)

Indeed, there were some commented lines in my **host.json** file 😳, remnants of a test I made long time ago.

{{< figure src="./image-1.png" alt="" caption="" >}}

## **🧑‍⚕️The diagnostic**

Removing these commented lines and deploying the project fixed the issue instantly and the HTTP-triggered function started to work as intended.

It seems that even if [comments are not supported](https://medium.com/@marycriv/why-json-doesnt-allow-comments-fe93f7106c62) in the JSON specification, the **In-Process** model used to ignore and skip these commented line in the host file. That doesn't seem to be the case with the **Isolated worker** model.

I later discovered several threads like the one below, where others have encountered the same issue. However, there doesn’t seem to be a fix on the horizon.

🔗 [Using comments in host.json fails silently for isolated worker using the ASP.NET integration · Issue #2855 · Azure/azure-functions-dotnet-worker](https://github.com/Azure/azure-functions-dotnet-worker/issues/2855)

## **💊The fix**

Since the compiler will not prevent the deployment of a function app project with a **host.json** with commented lines, this can lead to big problems.

For example, if a developer inadvertently commit a commented host file and deploys the function app, HTTP trigger issues will only be caught at **runtime** and might take a while to diagnose.

Sometimes, there might actually be a good reason for these commented lines. For instance, developers might want to test certain host configurations or toggle parameters on and off without losing track of their original settings.

Here’s how I updated my project build configurations and release pipeline to ensure this never happens, whether running locally or deployed in Azure.

The goal is to remove the **host.json** file commented lines in the build output folder while allowing them in source control. _Special mention to **GitHub Copilot** who took care of crafting the regex and Powershell scripts for me. Thank you buddy_ 😉!

For this to work **locally**, I added this **PostBuild** command in the projects .cdsproj file.

```
  <Target Name="PostBuild" AfterTargets="PostBuildEvent">
    <Exec Command="powershell -NoProfile -ExecutionPolicy Bypass -Command &quot;Get-ChildItem -Path '$(TargetDir)' -Recurse -Filter 'host.json' | ForEach-Object { (Get-Content $_.FullName) | Where-Object { $_ -notmatch '^\s*//'} | Set-Content $_.FullName }&quot;" />
  </Target>
```

For it to work in my **Azure Devops** release pipeline, I had to run this powershell script **before** the build step of the pipeline

```
  - pwsh: |
      Get-ChildItem -Path '$(Build.SourcesDirectory)' -Recurse -Filter 'host.json' | ForEach-Object {
        Write-Host "Processing file: $($_.FullName)"
        (Get-Content $_.FullName) | Where-Object { $_ -notmatch '^\s*//' } | Set-Content $_.FullName
      }
     displayName: 'Remove commented lines from host.json files'
```

And that's it, I don't have to worry anymore about breaking my HTTP triggered Azure Functions because of invalid host files.

Hope this helps.

## **Links**
{{< linkcard url="https://learn.microsoft.com/en-us/azure/azure-functions/migrate-dotnet-to-isolated-model?WT.mc_id=DX-MVP-5004959&tabs=net8" title="Migrate .NET function apps from the in-process model to the isolated worker model" summary="This article shows you how to migrate your existing .NET function apps running on the in-process model to the isolated worker model." image="/linkcards/4fac7452f522bab5.png" domain="learn.microsoft.com" new_tab="true" nofollow="true" >}}


{{< linkcard url="https://www.elevenforum.com/t/net-6-will-reach-end-of-support-on-november-12-2024.26899/#:~:text=.NET%206%20will%20reach%20end%20of%20support%20on%2cto.NET%208%20before%20this%20date%20to%20stay%20supported." title=".NET 6 will reach End of Support on November 12, 2024" summary=".NET Blog: .NET 6 will reach end of support on Nov 12, 2024. After that, Microsoft will no longer provide updates for .NET 6. Security fixes and technical support will no longer be available for .NET 6. You’ll need to update to .NET 8 before this date to stay supported. Commercial support for…" image="/linkcards/f82e8c9044727271.jpg" domain="www.elevenforum.com" new_tab="true" nofollow="true" >}}


{{< linkcard url="https://github.com/Azure/Azure-Functions/issues/2425" title="Migrating azure functions to .net8 isolated, function hangs when triggered · Issue #2425 · Azure/Azure-Functions" summary="I am migrating from Azure Functions .Net 6 app to .Net 8 isolated and I am testing a demo function called HttpTriggerCSharp by debugging it in Rider (MacOs). The breakpoints have a green tick and w…" image="/linkcards/447ae8cd404918e2.png" domain="github.com" new_tab="true" nofollow="true" >}}


{{< linkcard url="https://github.com/Azure/azure-functions-dotnet-worker/issues/2855" title="Using comments in host.json fails silently for isolated worker using the ASP.NET integration · Issue #2855 · Azure/azure-functions-dotnet-worker" summary="When using comments in host.json the file is not loaded and no error is reported. All settings set in host.json are ignored and the default settings are applied. There is no log output related to t…" image="/linkcards/52c89201ad8798fe.png" domain="github.com" new_tab="true" nofollow="true" >}}


{{< linkcard url="https://medium.com/@marycriv/why-json-doesnt-allow-comments-fe93f7106c62" title="Why JSON doesn’t allow comments" summary="Comments are probably one of the most under-appreciated aspects of coding. When you’re typing at lightning speed while listening to The…" image="/linkcards/8b31d1707b004acd.gif" domain="medium.com" new_tab="true" nofollow="true" >}}