Netherite is a distributed workflow execution engine for [Durable Functions](https://github.com/Azure/azure-functions-durable-extension) (DF) and the [Durable Task Framework](https://github.com/Azure/durabletask/) (DTFx).
As Netherite is intended to be a drop-in backend replacement, it does not modify the application API. Existing DF and DTFx applications can switch to this backend with little effort.
To get started, you can either try out the sample, or take an existing DF app and switch it to the Netherite backend. You can also read our [documentation](https://microsoft.github.io/durabletask-netherite/#/README).
For a comprehensive quick start on using Netherite with Durable Functions, take a look at [hello sample walkthrough](https://microsoft.github.io/durabletask-netherite/#/hello-sample.md), and the associated [video content](https://microsoft.github.io/durabletask-netherite/#/hello-sample.md?id=walk-through-on-youtube-%f0%9f%8e%a5).
We included several scripts that make it easy to build, run, and deploy this application, both locally and in the cloud.
Also, this sample is a great starting point for creating your own projects.
**Configure an existing Durable Functions app for Netherite.**
- Add the NuGet package `Microsoft.Azure.DurableTask.Netherite.AzureFunctions` to your functions project (if using .NET) or your extensions project (if using TypeScript or Python).
- Add `"type" : "Netherite"` to the `storageProvider` section of your host.json. See [recommended host.json settings](https://microsoft.github.io/durabletask-netherite/#/settings.md).
- Configure your function app to run on 64 bit, if not already the case. You can do this in the Azure portal, or using the Azure CLI. Netherite does not run on 32 bit.
- Create an EventHubs namespace. You can do this in the Azure portal, or using the Azure CLI.
- Configure `EventHubsConnection` with the connection string for the Event Hubs namespace. You can do this using an environment variable, or with a function app configuration settings.
**Configure an existing Durable Task Application for Netherite.**
If you have an application that uses the Durable Task Framework already, and want to configure it to use Netherite as the backend, do the following:
- Create an EventHubs namespace. You can do this in the Azure portal, or using the Azure CLI.
- Add the NuGet package `Microsoft.Azure.DurableTask.Netherite` to your project.
- Update the server startup code to construct a `NetheriteOrchestrationService` object with the required settings, and then pass it as an argument to the constructors of `TaskHubClient` and `TaskHubWorker`.
For more information, see the [DTFx sample](https://github.com/microsoft/durabletask-netherite/blob/dev/samples/HelloDTFx/HelloDTFx/Program.cs).
The default Azure Storage engine stores messages in Azure Storage queues and instance states in Azure Storage tables.
It executes large numbers of small storage accesses.
For example, executing a single orchestration with three activities may require a total of 4 dequeue operations, 3 enqueue operations, 4 table reads, and 4 table writes.
Thus, the overall throughput quickly becomes limited by how many I/O operations Azure Storage allows per second.
To learn more about the Netherite architecture, our [VLDB 2022 paper](https://www.microsoft.com/en-us/research/uploads/prod/2022/07/p1591-burckhardt.pdf) is the best reference.
There is also an earlier preprint [paper on arXiv](https://arxiv.org/abs/2103.00033).
- Instance queries and purge requests are not issued directly against Azure Storage, but are processed by the function app. Thus, the performance (latency and throughput) of queries heavily depends on
the current scale status and load of the function app. In particular, queries do not work if the function app is stopped, and may experience cold start symptoms on consumption plans.
- Scale out of activities (not just orchestrations) is limited by the [partition count configuration setting](https://microsoft.github.io/durabletask-netherite/#/settings?id=partition-count-considerations),
which defaults to 12. If you need to scale out beyond 12 workers, you should increase it prior to starting you application (it cannot be changed after the task hub has been created).
- The [rewind feature](https://learn.microsoft.com/en-us/azure/azure-functions/durable/durable-functions-http-api#rewind-instance-preview) is not available on Netherite.
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