When would you use App Service WebJobs versus Azure Functions for background work in a .NET application?

WebJobs vs Azure Functions for background work in a .NET system

Compares App Service WebJobs and Azure Functions for queue processing, scheduled tasks, scaling, deployment ownership, and operational isolation.

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TL;DR

I would use WebJobs when the background work naturally belongs with an App Service app and the team wants a simple worker deployed alongside that environment. I would use Azure Functions when event-driven triggers, timers, queue triggers, or independent scaling are a better fit. In both cases I would avoid hiding long work inside HTTP requests or fire-and-forget tasks from controllers.

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Background processing options, scaling model, triggers, deployment ownership, operational isolation, and queue-driven design.

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Why this question matters
WebJobs and Azure Functions can both run .NET background work, but they differ in lifecycle, triggers, scaling, isolation, deployment, and operational ownership. The workload and its failure behavior should determine the model.
I would use WebJobs when the background work naturally belongs with an App Service app and the team wants a simple worker deployed alongside that environment. I would use Azure Functions when event-driven triggers, timers, queue triggers, or independent scaling are a better fit. In both cases I would avoid hiding long work inside HTTP requests or fire-and-forget tasks from controllers.
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The choice depends on ownership, triggers, scaling, deployment, and operational isolation. WebJobs can be convenient for jobs that share code and lifecycle with the web app, but they can also share App Service plan resources. Functions fit event-driven work well and give more natural trigger bindings, but they bring their own hosting model, cold start considerations, configuration, and deployment flow. Either way I would define retries, poison handling, concurrency, identity, logs, alerts, and job idempotency.

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Details

Using fire-and-forget Task.Run inside the API instead of a real worker boundary.
Ignoring that WebJobs can share capacity with the web app.
Choosing Functions without understanding trigger and retry behavior.
No poison message or idempotency plan.

When would you use App Service WebJobs versus Azure Functions for background work in a .NET application?

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When would you use App Service WebJobs versus Azure Functions for background work in a .NET application?

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