Host ID collisions in placeholder mode?

[jeremy-skippen-jbhifi]

Issue description

I've recently updated a dotnet-isolated function deployment to add a staging slot. Both the production and the staging slot share a storage account and have host ids set explicitly. Since then, periodically the following error has been reported in the portal:

A collision for Host ID 'functionsv4x64dotnetisolated8pla' was detected in the configured storage account. For more information, see https://aka.ms/functions-hostid-collision.

Feeling is that this is happening when both slots are started in placeholder mode, possibly because of something happening in the platform outside of the host. E.g. 1 occurrence happened at 12AM UTC. IIS app pool recycle?

Assuming the placeholder function that's being started is called functionsv4x64dotnetisolated8placeholdertemplatesite based on some other reports:

• Host ID Collision Error Azure-Functions#2049 (comment)
• Placeholder is assigned to an app before worker is initialized #9958

Configuration

App Service plan

• SKU: Y1
• Operating System: Windows
• Location: Australia East

Host

• Host version: 4.36.0.23246 / 4.1036.3.23284

Stack settings

• Runtime version: ~4
• Stack: .NET
• .NET Version: .NET 8 Isolated

Platform settings

• Platform: 64 Bit
• Managed pipeline version: Integrated

Possible solutions

• Don't do host id validation when in placeholder mode (src\WebJobs.Script\Host\ScriptHostIdProvider.cs@GetHostIdAsync)
• Use shorter function names for placeholder functions