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Lab 4 - Creating a Function App Project

Goal

The goal of this lab is to create a basic Function App with a Servicebus triggered function and to determine it is connected correctly and receiving detected NEO messages from the topic.

Steps

1. Create a Function App with a ServiceBusTrigger function

With your IDE of choice create a Function App (.NET Core v3) (suggested name: NeoEventProcessing) with a Servicebus Topic triggered function. The suggested name for the function, and the class, is NeoEventProcessingClientServicebus.

  • When asked, specify that we want to use the Storage Emulator which is used to run the app locally.

  • Specify the following Servicebus settings in the ServiceBusTrigger attribute:

    • Connectionstring setting name: NEOEventsTopic
    • Topic name: neo-events
    • Subscription name: <subscriptionname> (get this from the blob json file that is created in the earlier previous lab)

The resulting servicebus function trigger should look something like this:

[ServiceBusTrigger("neo-events", "<YOUR_PERSONAL_TOPIC_SUBSCRIPTIONNAME>", Connection = "NEOEventsTopic")]string message,

The trigger now has a connection name which will be looked up in the application settings. But there's is no actual connectionstring specified yet.

Locate the local.settings.json file in your local function folder and add the connection name (NEOEventsTopic) and the connectionstring (output from the previous lab):

{
    "IsEncrypted": false,
  "Values": {
    "AzureWebJobsStorage": "UseDevelopmentStorage=true",
    "FUNCTIONS_V2_COMPATIBILITY_MODE": true,
    "FUNCTIONS_WORKER_RUNTIME": "dotnet",
    "NEOEventsTopic": "<servicebus_connectionstring>"
  }
}

Also make sure to add the FUNCTIONS_V2_COMPATIBILITY_MODE:true setting. This ensures correct json (de)serialization, which is an unresolved issue in Azure Functions v3 at the moment.

2. Run the Function App locally

Now that your Function App is configured to receive messages let's try and run it locally to verify it does. Add a breakpoint to the Servicebus triggered function and run/debug your Function App locally.

The Azure Function Runtime should start in a console window and show some diagnostic information. If there are any issues with storage and/or service bus configuration we will see the errors in this console.

What is format of the message we're receiving?

Are there other types which are also acceptable instead of string?

3. Convert the messages to DetectedNeoEvent objects

Currently the inconming mesage is of type string and the content is json. Let's convert this to the strongly typed model so we can work with the data more easily.

The DetectedNeoEvent type is part of this NuGet package: Demo.NEO.Models. You can download the package by connecting to this NuGet feed:

https://pkgs.dev.azure.com/marcduiker/Building Resilient Workflows With Durable Functions/_packaging/Public/nuget/v3/index.json

If you aren't configuring the feed using an IDE you can also add a file named nuget.config to the root of your solution with the following content:

<configuration>
  <packageSources>
    <add key="Xasa" value="https://pkgs.dev.azure.com/marcduiker/Building Resilient Workflows With Durable Functions/_packaging/Public/nuget/v3/index.json" />
  </packageSources>
</configuration>

Once you have added the Demo.NEO.Models package to the project change the type of the message argument to DetectedNeoEvent:

[ServiceBusTrigger("neo-events", "<YOUR SUBSCRIPTION KEY>", Connection = "NEOEventsTopic")]DetectedNeoEvent detectedNeoEvent,

4. Run the Function App locally

Run your Function App locally and verify we're receiving DetectedNeoEvent objects.

5. Optional: Moving Attribute Parameters to App Settings

When we look at the ServiceBusTrigger attribute the topic name and the subscription name are hardcoded in the attribute parameters. You can move the actual values to the local.settings.json file as key-value pairs and reference the settings in the attribute by using %KEY%as the parameter value.

[ServiceBusTrigger("%TopicName%", "%SubscriptionName%", Connection = "NEOEventsTopic")]DetectedNeoEvent detectedNeoEvent,

If everything works as expected continue with the next lab to create an orchestration client.