Today on Azure Friday: Durable Functions in Azure Functions

Chris Gillum joins Scott Hanselman to discuss a new extension of Azure Functions known as Durable Functions. Durable Functions is a programming model for authoring stateful, reliable, and serverless ...

Azure Friday

Chris Gillum

Microsoft

Feb 27, 2018

You can use the samples in the GitHub repository as a reference. For example, there are two sample functions that show how you can trigger new orchestration instances:

HttpTrigger: https://github.com/Azure/azure-functions-durable-extension/blob/master/samples/csx/HttpStart/run.csx

ManualTrigger: https://github.com/Azure/azure-functions-durable-extension/blob/master/samples/csx/ManualStart/run.csx

From these samples, you should be able to figure out how to use other trigger types. Here is an example of how you might start an orchestration from a blob trigger:

run.csx

#r "Microsoft.Azure.WebJobs.Extensions.DurableTask"

using System;

public static async Task Run(string blobData, DurableOrchestrationClient starter, TraceWriter log)
{
    log.Info("Starting orchestration.");
    string instanceId = await starter.StartNewAsync("MyOrchestrator", blobData);
    log.Info($"Started orchestration with ID = '{instanceId}'.");   
}

function.json

{
  "bindings": [
    {
      "type": "blobTrigger",
      "direction": "in",
      "name": "blobData"
    },
    {
      "name": "starter",
      "type": "orchestrationClient",
      "direction": "in"
    }
  ],
  "disabled": false
}

Ivan Buzyka

Copper Contributor

Feb 28, 2018

Hi Chris,

First of all thank you for your reply. I am very excited to hear directly from you :)

I managed to get BlobTrigger working.

However, I got another exception when trigger started:

Exception while executing function: DurableEveDataAggregationEntryPoint

Microsoft.Azure.WebJobs.Host.FunctionInvocationException : Exception while executing function: DurableEveDataAggregationEntryPoint ---> Newtonsoft.Json.JsonSerializationException : Error getting value from 'ReadTimeout' on 'Microsoft.Azure.WebJobs.Host.Blobs.WatchableReadStream'. ---> System.InvalidOperationException : Timeouts are not supported on this stream.

   at System.IO.Stream.get_ReadTimeout()

   at Microsoft.Azure.WebJobs.Host.Blobs.DelegatingStream.get_ReadTimeout() at C:\projects\azure-webjobs-sdk-rqm4t\src\Microsoft.Azure.WebJobs.Host\Blobs\DelegatingStream.cs : 53

   at lambda_method(Closure ,Object )

   at Newtonsoft.Json.Serialization.ExpressionValueProvider.GetValue(Object target) 

   End of inner exception

   at Newtonsoft.Json.Serialization.ExpressionValueProvider.GetValue(Object target)

   at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.CalculatePropertyValues(JsonWriter writer,Object value,JsonContainerContract contract,JsonProperty member,JsonProperty property,JsonContract& memberContract,Object& memberValue)

   at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeObject(JsonWriter writer,Object value,JsonObjectContract contract,JsonProperty member,JsonContainerContract collectionContract,JsonProperty containerProperty)

   at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeValue(JsonWriter writer,Object value,JsonContract valueContract,JsonProperty member,JsonContainerContract containerContract,JsonProperty containerProperty)

   at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.Serialize(JsonWriter jsonWriter,Object value,Type objectType)

   at Newtonsoft.Json.JsonSerializer.SerializeInternal(JsonWriter jsonWriter,Object value,Type objectType)

   at Newtonsoft.Json.JsonSerializer.Serialize(JsonWriter jsonWriter,Object value)

   at DurableTask.Core.Serializing.JsonDataConverter.Serialize(Object val…

That happens on both local runtime when debugging as well as on Azure when deployed.

As far as I understood the object of type Stream cannot be serialized in order to be passed to the orchestrator. It is very possible that I do something wrong :) Therefore, I hope you can give an advice.

See that primitive example that I am trying to run here https://github.com/ivanbuzyka/Azure.DurableFunctions.BlobTriggerExperiment/blob/master/DurableEveDataAggregator.cs

P.S. As soon as I get that thing working, I promise to share an example and blog a bit about that

Ivan Buzyka
Copper Contributor
Feb 28, 2018
Just updated the code, so the orchestrator gets the name of the triggering blob from orchestration client and the access to the Stream of that blob was organized by using BlobContainer binding and that blob name. Here is the commit: https://github.com/ivanbuzyka/Azure.DurableFunctions.BlobTriggerExperiment/commit/5237538e6bea269ac2ef221f81757939cf1eb092

I hope that looks better.
- Chris Gillum
  Microsoft
  Feb 28, 2018
  Thanks! Yes, only JSON-serializeable types can be used as arguments to orchestrator or activity functions. I think that explains the exception you were seeing earlier. Passing the blob name instead of the stream is the right way to go.
  
  One thing I noticed is that you are calling blob storage directly from your orchestrator function. We actually discourage doing any I/O in an orchestrator function, and instead suggest that you do I/O (such as calling into blob storage) only from activity functions. See this documentation for more information on why: https://docs.microsoft.com/en-us/azure/azure-functions/durable-functions-checkpointing-and-replay (especially the part about code constraints).

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