topic Re: Fabric Extensibility Toolkit: Development workload startup failure in Data Engineering

Fabric Extensibility Toolkit: Development workload startup failure

shas902 — Sun, 04 Jan 2026 23:21:16 GMT

I was replicating youtube video demo to create Hello World workload. On my personal free GitHub account I had limitation to allocate machine type to codespace only upto 4 cores while requirement was 8 cores. I asked GitHub Copilot to fix the repo files for a 4 core machine type.

Error in Micrsoft Fabric Experience:
Development workload startup failure.
The development workload startup has failed due to an inactive local server or a configuration issue.

Solution:

Fixed: OOM Errors on 4-Core Codespaces

The Problem

The development server crashes with Out-of-Memory (OOM) errors when running the Fabric Extensibility Toolkit on standard 4-core Codespace machines.

Root Cause

Webpack bundling for this toolkit is memory-intensive. On 4-core machines (which typically only have 8GB RAM), the default Node.js heap limit and source map generation exceed the available system memory.

Solution Applied

1. Increased Node Heap Size

Updated the start script in package.json to allocate more memory to the Node process.

File: package.json
Change: Increased --max-old-space-size from 4GB to 6GB.

JSON

// Before
"start:codespace": "node --max-old-space-size=4096 ..."

// After
"start:codespace": "node --max-old-space-size=6144 ..."

2. Conditional Source Maps

Disabled source maps specifically when running inside a Codespace environment to reduce the memory footprint by approximately 2GB.

File: Workload/webpack.dev.js
Change: Added a check for the CODESPACES environment variable.

JavaScript

// Before
devtool: 'source-map' 

// After
devtool: process.env.CODESPACES ? false : 'source-map'

3. Environment Cleanup

Performed a manual cleanup of leftover build assets and cache from previous failed setup attempts to ensure a clean slate.

Result

The Dev server and gateway now start successfully on 4-core machines without memory crashes.

[!TIP] Recommendation: While these fixes stabilize the 4-core experience, upgrading to an 8-core machine is still recommended for optimal build speed and performance.

Re: Fabric Extensibility Toolkit: Development workload startup failure

lbendlin — Mon, 05 Jan 2026 16:26:12 GMT

What is your question? Or are you looking for the Blog section? https://community.fabric.microsoft.com/t5/Fabric-community-blogs/ct-p/fabricblogs

Re: Fabric Extensibility Toolkit: Development workload startup failure

deborshi_nag — Mon, 05 Jan 2026 18:35:11 GMT

Hi @shas902

Thank you for posting, however it is difficult to interpret if you're referring to an issue with the Data Engineering experience of Microsoft Fabric, which is what the forum is for. Woud you be able to expand on your post please?

Please leave a Kudos or accept it as a Solution!

Re: Fabric Extensibility Toolkit: Development workload startup failure

v-prasare — Mon, 12 Jan 2026 11:53:06 GMT

Hi @shas902,

As our super user @lbendlin, suggested refer below blog post section so that other community members can benefit from your experience more easily.

https://community.fabric.microsoft.com/t5/Power-BI-Community-Blog/bg-p/community_blog

Thanks,

Prashanth Are

Re: Fabric Extensibility Toolkit: Development workload startup failure

v-prasare — Fri, 16 Jan 2026 08:48:47 GMT

Hi @shas902,

Since we haven’t heard back from you yet, could you please let us know whether you were able to post this in the Community Blog section? If you need any help please reach out us in Fabric community forum.

Thanks,

Prashanth