Azure Functions Core Tools startup is significantly delayed due to slow CDN fetch for extension bundle index

[Pratikkapadia7]

When running Azure Functions Core Tools locally (func start), the startup takes 1–2 minutes, even when the extension bundle is pinned and already present locally.

After investigating with --verbose, I noticed that the CLI always makes a call to:
https://cdn.functions.azure.com/public/ExtensionBundles/Microsoft.Azure.Functions.ExtensionBundle/index.json

This call introduces a long delay in environments with slow or throttled access to Azure's CDN (in my case, from India). Even with the bundle version pinned exactly:
"extensionBundle": { "id": "Microsoft.Azure.Functions.ExtensionBundle", "version": "[4.24.2, 4.24.2]" }

the CLI still makes the network request. Since the bundle is already available locally, this fetch feels unnecessary and slows down the dev experience substantially.

Environment
OS: macOS
Core Tools Version: 4.1.0
Runtime: Node.js
Bundle version: 4.24.2
CDN response time: ~60–90 seconds

Additional Info

• This was working fine a few days ago — startup was fast and no CDN calls were noticeable.

• I even tried creating a brand new function app, and the issue persists.

• The slow startup is blocking local development and making iteration very difficult.

[simonness]

Happening again on 7th February 2026:

[cbries]

Yep, for me as well. I was puzzled for the last 2-3 hours. Now it seems to work again, locally, for me.
Nope, still not working.
func start hangs because of this issue.

[JoelLeach]

On Windows, temporary workaround is to add this to C:\Windows\System32\drivers\etc\hosts until they get it up and running again:

#Workaround Azure Functions CDN outage
127.0.0.1 cdn.functions.azure.com

Don't forget to remove it later!

[offbeatful]

I don't know how many issues needs to be created...

#2060
#3821
#4696

Please, make sure that func start by default does not go anywhere or check anything, especially if only http/cron triggers are used.

Every outage disrupts local development and integration testing that rely on functions emulator.

[liliankasem]

Issue should be fixed as part of the next core tools release (v4.8.0, eta for release is end of this week) - please open a new issue if you're on 4.8.0 and experiencing problems with this new feature - thanks!