Merge pull request #287759 from mattchenderson/azfd0011

Clarifying AZFD0011 event details

Author: Jill Grant

articles/azure-functions/errors-diagnostics/diagnostic-events/azfd0011.md

@@ -9,7 +9,7 @@ ms.date: 01/24/2024
 
 # AZFD0011: The FUNCTIONS_WORKER_RUNTIME setting is required
 
-This event occurs when a function app doesn't have the `FUNCTIONS_WORKER_RUNTIME` application setting, which is required.
+This event occurs when a function app doesn't have a value for the `FUNCTIONS_WORKER_RUNTIME` application setting, which is required.
 
 | | Value |
 |-|-|
@@ -18,18 +18,20 @@ This event occurs when a function app doesn't have the `FUNCTIONS_WORKER_RUNTIME
 
 ## Event description
 
-The `FUNCTIONS_WORKER_RUNTIME` application setting indicates the language or language stack on which the function app runs, such as `python`. For more information on valid values, see the [`FUNCTIONS_WORKER_RUNTIME`](../../functions-app-settings.md#functions_worker_runtime) reference.
+The `FUNCTIONS_WORKER_RUNTIME` application setting indicates the language or language stack on which the function app runs, such as `python`. For more information on valid values, see the [`FUNCTIONS_WORKER_RUNTIME`][fwr] reference.
 
-While not currently required, you should always specify `FUNCTIONS_WORKER_RUNTIME` for your function apps. When you don't have this setting and the Functions host can't determine the correct language or language stack, you might see exceptions or unexpected behaviors. 
+You should always specify a valid `FUNCTIONS_WORKER_RUNTIME` for your function apps. When you don't have this setting and the Functions host can't determine the correct language or language stack, you might see performance degradations, exceptions, or unexpected behaviors. To ensure that your application operates as intended, you should explicitly set it in all of your existing function apps and deployment scripts.
 
-Because `FUNCTIONS_WORKER_RUNTIME` is likely to become a required setting, you should explicitly set it in all of your existing function apps and deployment scripts to prevent any downtime in the future.
+The value of `FUNCTIONS_WORKER_RUNTIME` should align with the language stack used to create the deployed application payload. If these do not align, you may see the [`AZFD0013`](./azfd0013.md) event.
 
 ## How to resolve the event
 
-In a production application, add `FUNCTIONS_WORKER_RUNTIME` to the [application settings](../../functions-how-to-use-azure-function-app-settings.md#settings).
+In a production application, set [`FUNCTIONS_WORKER_RUNTIME` to a valid value][fwr] in the [application settings](../../functions-how-to-use-azure-function-app-settings.md#settings). The value should align with the language stack used to create the application payload.
 
-When running locally in Azure Functions Core Tools, also add `FUNCTIONS_WORKER_RUNTIME` to the [local.settings.json file](../../functions-develop-local.md#local-settings-file).
+When running locally in Azure Functions Core Tools, also set [`FUNCTIONS_WORKER_RUNTIME` to a valid value][fwr] in the [local.settings.json file](../../functions-develop-local.md#local-settings-file). The value should align with the language stack used in the local project.
 
 ## When to suppress the event
 
 This event shouldn't be suppressed.
+
+[fwr]: ../../functions-app-settings.md#functions_worker_runtime