Merge pull request #289709 from lilyjma/durable-flex

Documenting workaround for reducing Durable cold start

Author: prmerger-automator[bot]

articles/azure-functions/durable/durable-functions-azure-storage-provider.md

@@ -280,6 +280,16 @@ If you are not seeing the throughput numbers you expect and your CPU and memory
 > [!TIP]
 > In some cases you can significantly increase the throughput of external events, activity fan-in, and entity operations by increasing the value of the `controlQueueBufferThreshold` setting in **host.json**. Increasing this value beyond its default causes the Durable Task Framework storage provider to use more memory to prefetch these events more aggressively, reducing delays associated with dequeueing messages from the Azure Storage control queues. For more information, see the [host.json](durable-functions-bindings.md#host-json) reference documentation.
 
+### Flex Consumption Plan 
+The [Flex Consumption plan](../flex-consumption-plan.md) is an Azure Functions hosting plan that provides many of the benefits of the Consumption plan, including a serverless billing model, while also adding useful features, such as private networking, instance memory size selection, and full support for managed identity authentication.
+
+Azure Storage is currently the only supported [storage provider](durable-functions-storage-providers.md) for Durable Functions when hosted in the Flex Consumption plan.
+
+You should follow these performance recommendations when hosting Durable Functions in the Flex Consumption plan:
+
+* Set the [always ready instance count](../flex-consumption-how-to.md#set-always-ready-instance-counts) for the `durable` group to `1`. This ensures that there is always one instance ready to handle Durable Functions related requests, thus reducing the application's cold start. 
+* Reduce the [queue polling interval](durable-functions-azure-storage-provider.md#queue-polling) to 10 seconds or less. Since this plan type is more sensitive to queue polling delays, lowering the polling interval will help increase the frequency of polling operations, thus ensuring requests are handled faster. However, more frequent polling operations will lead to a higher Azure Storage account cost. 
+
 ### High throughput processing
 
 The architecture of the Azure Storage backend puts certain limitations on the maximum theoretical performance and scalability of Durable Functions. If your testing shows that Durable Functions on Azure Storage won't meet your throughput requirements, you should consider instead using the [Netherite storage provider for Durable Functions](durable-functions-storage-providers.md#netherite).

articles/azure-functions/durable/durable-functions-storage-providers.md

@@ -197,6 +197,7 @@ There are many significant tradeoffs between the various supported storage provi
 | Price-performance configurable? | ❌ No | ✅ Yes (Event Hubs TUs and CUs) | ✅ Yes (SQL vCPUs) |
 | Disconnected environment support | ❌ Azure connectivity required | ❌ Azure connectivity required | ✅ Fully supported |
 | Identity-based connections | ✅ Fully supported |❌ Not supported | ⚠️ Requires runtime-driven scaling |
+| [Flex Consumption plan](../flex-consumption-plan.md) | ✅ Fully supported ([see notes](./durable-functions-azure-storage-provider.md#flex-consumption-plan)) |❌ Not supported | ❌ Not supported |
 
 ## Next steps
 

articles/azure-functions/durable/quickstart-mssql.md

@@ -16,9 +16,11 @@ Durable Functions supports several [storage providers](durable-functions-storage
 
 > [!NOTE]
 >
-> - The MSSQL back end was designed to maximize application portability and control over your data. It uses [Microsoft SQL Server](https://www.microsoft.com/sql-server/) to persist all task hub data so that users get the benefits of a modern, enterprise-grade database management system (DBMS) infrastructure. To learn more about when to use the MSSQL storage provider, see the [storage providers overview](durable-functions-storage-providers.md).
+> - The MSSQL backend was designed to maximize application portability and control over your data. It uses [Microsoft SQL Server](https://www.microsoft.com/sql-server/) to persist all task hub data so that users get the benefits of a modern, enterprise-grade database management system (DBMS) infrastructure. To learn more about when to use the MSSQL storage provider, see the [storage providers overview](durable-functions-storage-providers.md).
 >
 > - Migrating [task hub data](durable-functions-task-hubs.md) across storage providers currently isn't supported. Function apps that have existing runtime data start with a fresh, empty task hub after they switch to the MSSQL back end. Similarly, the task hub contents that are created by using MSSQL can't be preserved if you switch to a different storage provider.
+>
+> - The MSSQL backend currently isn't supported by Durable Functions when running on the [Flex Consumption plan](../flex-consumption-plan.md). 
 
 ## Prerequisites
 

articles/azure-functions/durable/quickstart-netherite.md

@@ -19,6 +19,8 @@ Durable Functions offers several [storage providers](durable-functions-storage-p
 > - Netherite was designed and developed by [Microsoft Research](https://www.microsoft.com/research) for [high throughput](https://microsoft.github.io/durabletask-netherite/#/scenarios) scenarios. In some [benchmarks](https://microsoft.github.io/durabletask-netherite/#/throughput?id=multi-node-throughput), throughput increased by more than an order of magnitude compared to the default Azure Storage provider. To learn more about when to use the Netherite storage provider, see the [storage providers](durable-functions-storage-providers.md) documentation.
 >
 > - Migrating [task hub data](durable-functions-task-hubs.md) across storage providers currently isn't supported. Function apps that have existing runtime data start with a fresh, empty task hub after they switch to the Netherite back end. Similarly, the task hub contents that are created by using MSSQL can't be preserved if you switch to a different storage provider.
+>
+> - The Netherite backend currently isn't supported by Durable Functions when running on the [Flex Consumption plan](../flex-consumption-plan.md). 
 
 ## Prerequisites
 

articles/azure-functions/flex-consumption-plan.md

@@ -3,7 +3,7 @@ title: Azure Functions Flex Consumption plan hosting
 description: Running your function code in the Azure Functions Flex Consumption plan provides virtual network integration, dynamic scale (to zero), and reduced cold starts.
 ms.service: azure-functions
 ms.topic: concept-article
-ms.date: 08/22/2024
+ms.date: 11/01/2024
 ms.custom: references_regions, build-2024
 # Customer intent: As a developer, I want to understand the benefits of using the Flex Consumption plan so I can get the scalability benefits of Azure Functions without having to pay for resources I don't need.
 ---
@@ -137,7 +137,7 @@ In Flex Consumption, many of the standard application settings and site configur
 Keep these other considerations in mind when using Flex Consumption plan during the current preview:
 
 + **Host**: There is a 30 seconds timeout for the app initialization. If your function app takes longer than 30 seconds to start you will see gRPC related System.TimeoutException entries. This timeout will be configurable and a more clear exception will be implemented as part of [this host work item](https://github.com/Azure/azure-functions-host/issues/10482).
-+ **Durable Functions**: Due to the per function scaling nature of Flex Consumption, to ensure the best performance for Durable Functions we recommend setting the [Always Ready instance count](./flex-consumption-how-to.md#set-always-ready-instance-counts) for the `durable` group to `1`. Also, with the Azure Storage provider, consider reducing the [queue polling interval](./durable/durable-functions-azure-storage-provider.md#queue-polling) to 10 seconds or less. Only Azure Storage is supported as a backend storage providers for Flex Consumption hosted durable functions.
++ **Durable Functions**: Azure Storage is currently the only supported [storage provider](./durable/durable-functions-storage-providers.md) for Durable Functions when hosted in the Flex Consumption plan. See [recommendations](./durable/durable-functions-azure-storage-provider.md#flex-consumption-plan) when hosting Durable Functions in the Flex Consumption plan.
 + **VNet Integration** Ensure that the `Microsoft.App` Azure resource provider is enabled for your subscription by [following these instructions](/azure/azure-resource-manager/management/resource-providers-and-types#register-resource-provider). The subnet delegation required by Flex Consumption apps is `Microsoft.App/environments`.
 + **Triggers**: All triggers are fully supported except for Kafka and Azure SQL triggers. The Blob storage trigger only supports the [Event Grid source](./functions-event-grid-blob-trigger.md). Non-C# function apps must use version `[4.0.0, 5.0.0)` of the [extension bundle](./functions-bindings-register.md#extension-bundles), or a later version. 
 + **Regions**: Not all regions are currently supported. To learn more, see [View currently supported regions](flex-consumption-how-to.md#view-currently-supported-regions).