Differences between isolated worker model and in-process model .NET Azure Functions
There are two process models for .NET functions:
|Isolated worker model||Your function code runs in a separate .NET worker process. Use with supported versions of .NET and .NET Framework. To learn more, see Develop .NET isolated worker process functions.|
|In-process model||Your function code runs in the same process as the Functions host process. Supports only Long Term Support (LTS) versions of .NET. To learn more, see Develop .NET class library functions.|
This article describes the current state of the functional and behavioral differences between the two models. To migrate from the in-process model to the isolated worker model, see Migrate .NET apps from the in-process model to the isolated worker model.
Execution mode comparison table
Use the following table to compare feature and functional differences between the two models:
|Feature/behavior||Isolated worker process||In-process3|
|Supported .NET versions||Long Term Support (LTS) versions,
Standard Term Support (STS) versions,
|Long Term Support (LTS) versions6|
|Binding extension packages||Microsoft.Azure.Functions.Worker.Extensions.*||Microsoft.Azure.WebJobs.Extensions.*|
|Model types exposed by bindings||Simple types
JSON serializable types
Service SDK types4
JSON serializable types
Service SDK types4
|HTTP trigger model types||HttpRequestData / HttpResponseData
HttpRequest / IActionResult (using ASP.NET Core integration)5
|HttpRequest / IActionResult5
HttpRequestMessage / HttpResponseMessage
|Output binding interactions||Return values in an expanded model with:
- single or multiple outputs
- arrays of outputs
|Return values (single output only),
|Imperative bindings1||Not supported - instead work with SDK types directly||Supported|
|Dependency injection||Supported (improved model consistent with .NET ecosystem)||Supported|
|Application Insights dependencies||Supported||Supported|
|Cold start times2||Configurable optimizations||Optimized|
1 When you need to interact with a service using parameters determined at runtime, using the corresponding service SDKs directly is recommended over using imperative bindings. The SDKs are less verbose, cover more scenarios, and have advantages for error handling and debugging purposes. This recommendation applies to both models.
2 Cold start times could be additionally impacted on Windows when using some preview versions of .NET due to just-in-time loading of preview frameworks. This impact applies to both the in-process and out-of-process models but can be noticeable when comparing across different versions. This delay for preview versions isn't present on Linux plans.
3 C# Script functions also run in-process and use the same libraries as in-process class library functions. For more information, see the Azure Functions C# script (.csx) developer reference.
5 ASP.NET Core types are not supported for .NET Framework.
6 .NET 8 is not yet supported on the in-process model, though it is available on the isolated worker model. For information about .NET 8 plans, including future options for the in-process model, see the Azure Functions Roadmap Update post.
Versions of the Functions runtime support specific versions of .NET. To learn more about Functions versions, see Azure Functions runtime versions overview. Version support also depends on whether your functions run in-process or isolated worker process.
To learn how to change the Functions runtime version used by your function app, see view and update the current runtime version.
The following table shows the highest level of .NET or .NET Framework that can be used with a specific version of Functions.
|Functions runtime version||Isolated worker process
(.NET class library)
|Functions 4.x||.NET 8.0
.NET Framework 4.83
|Functions 1.x4||n/a||.NET Framework 4.8|
1 Per the .NET Official Support Policy, .NET 7 will reach end of support on May 14, 2024.
2 Per the .NET Official Support Policy, .NET 6 will reach end of support on November 12, 2024.
3 Build process also requires .NET 6 SDK.
4Support will end for version 1.x of the Azure Functions runtime on September 14, 2026. We highly recommend that you migrate your apps to version 4.x for full support.
For the latest news about Azure Functions releases, including the removal of specific older minor versions, monitor Azure App Service announcements.