Azure Function - In-process model vs Isolated worker model

 In-process model

• Your function code runs inside the same process as the Azure Functions runtime
• Uses the WebJobs SDK.

[FunctionName("TimetriggerFunction")]

What this means

• Used in:

  • Azure Functions v1–v4 (in-process)

• Namespace: Microsoft.Azure.WebJobs

• Runs inside the same process as the Azure Functions runtime

• Uses:

• ILogger for logging

• TimerInfo from Microsoft.Azure.WebJobs

Characteristics

• Tight coupling to the Functions runtime

• Faster startup (historically)

• More magic / implicit behavior

• Not recommended for new apps going forward

2. Isolated worker model

• Your function runs in a separate .NET process from the Azure Functions runtime.
• Communicates with the runtime over gRPC.

[Function("TimetriggerFunction")]

What this means

• Used in:

  • Azure Functions v4+ isolated worker

• Namespace: Microsoft.Azure.Functions.Worker

• Runs in a separate .NET process from the runtime

• Uses:

• FunctionContext instead of ILogger

• Logging via context.GetLogger(...)

Characteristics

• Decoupled from the Functions runtime

• Better:

  • Dependency injection

  • Versioning control

  • Middleware support

• Required for:

• .NET 8

• Future Azure Functions development

Key Differences at a Glance

Feature	[FunctionName]	[Function]
Hosting model	In-process	Isolated worker
Runtime coupling	Tight	Loose
Logging	ILogger	FunctionContext
Namespace	WebJobs	Functions.Worker
.NET 8 support	❌ No	✅ Yes
Recommended for new apps	❌ No	✅ Yes

Summary

In-process = older, tightly coupled, simpler
Isolated worker = modern, decoupled, flexible, future-proof