Azure Course Labs

Functions: Service Bus to Multiple Outputs

Functions and messaging go together very nicely when you build apps using asynchronous event publishing. Your main app might push messages to a Service Bus topic and that can trigger a function which adds a new feature.

In this lab we’ll use the Service Bus trigger and see how functions look with multiple outputs - in this case we’ll write to Table Storage and publish a message to a Service Bus queue.

Reference

Service Bus Topic function writing to Table Storage & queue

The scenario is an application where we have multiple suppliers who can quote to provide products. There are two functions in the TopicToTableAndQueue directory:

TopicToTableAndQueue/Supplier1Quote.cs - listens on a topic subscription for an incoming request, saves the response to table storage and posts a message to a queue
TopicToTableAndQueue/Supplier2Quote.cs - does the same as Supplier1Quote but with a different pricing engine and a deliberate delay

These attibutes take care of the trigger and bindings:

[ServiceBusTrigger] sets the function to run when messages are delivered to the QuoteRequestTopic and either the Supplier1Subscription or Supplier2Subscription
[Table] is an output binding which will create an entity in Table Storage in the table quotes
[ServiceBus] is another output binding which will send a message to the queue QuoteStoredQueue to notify that the quote has been saved

Service Bus topics can have multiple subscriptions, which each get a copy of every message. This scenario models two separate processes (which in the real world would be calling different supplier APIs), which have different latencies. Each process is a function with its own subsciption so they can work at their own pace.

For reference</summary>

Here’s how the function was created:

func init TopicToTableAndQueue --dotnet 

cd TopicToTableAndQueue

dotnet add package Microsoft.Azure.WebJobs.Extensions.ServiceBus --version 5.8.0
dotnet add package Microsoft.Azure.WebJobs.Extensions.Tables --version 1.0.0

func new --name Supplier1Quote --template ServiceBusTopicTrigger
func new --name Supplier2Quote --template ServiceBusTopicTrigger

</details>

Test the function locally

There are no Service Bus emulators, so you can’t run the function entirely locally, you’ll need to create this dependency in Azure first:

a Service Bus Namespace (Standard SKU)
a queue called QuoteStoredQueue in the namespace
a topic called QuoteRequestTopic in the namespace
two subsctriptions called Supplier1Subscription and Supplier2Subscription in the topic

Start the Azure Storage emulator which the function will use:

docker run -d -p 10000:10000 -p 10001:10001 -p 10002:10002 --name azurite mcr.microsoft.com/azure-storage/azurite

And create the file labs/functions/servicebus/TopicToTableAndQueue/local.settings.json with your own Service Bus connection string:

{
    "IsEncrypted": false,
    "Values": {
        "AzureWebJobsStorage": "UseDevelopmentStorage=true",
        "FUNCTIONS_WORKER_RUNTIME": "dotnet",
        "ServiceBusInputConnectionString" : "<your-connection-string>",
        "ServiceBusOutputConnectionString" : "<your-connection-string>",
        "OutputTableStorageConnectionString": "UseDevelopmentStorage=true"
    }
}

You can run the function locally when you have all the dependencies:

cd labs/functions/servicebus/TopicToTableAndQueue

func start

In the Azure Portal, send a message to the Topic:

{
    "QuoteId" : "42bf48b5-8531-48b3-82e0-91af19df6351", 
    "ProductCode": "PR-123",
    "Quantity" : 19
}

You should see output like this in your function:

[2022-11-07T21:56:55.436Z] Supplier1 saved quote response for ID: 42bf48b5-8531-48b3-82e0-91af19df6351
[2022-11-07T21:56:55.436Z] Supplier2 saved quote response for ID: 42bf48b5-8531-48b3-82e0-91af19df6351
[2022-11-07T21:56:55.505Z] Executed 'Supplier1Quote' (Succeeded, Id=58895544-27e9-4a52-99a2-7cf0ff3596c9, Duration=117ms)
[2022-11-07T21:56:55.505Z] Executed 'Supplier2Quote' (Succeeded, Id=31a6f011-0cdf-4941-90d8-92e42031c8f7, Duration=117ms)

And you can check the quotes table has been created in the emulator (or use Storage Explorer to browse):

az storage table list --connection-string "DefaultEndpointsProtocol=http;AccountName=devstoreaccount1;AccountKey=Eby8vdM02xNOcqFlqUwJPLlmEtlCDXJ1OUzFT50uSRZ6IFsuFq2UVErCz4I6tq/K1SZFPTOtr/KBHBeksoGMGw==;TableEndpoint=http://127.0.0.1:10002/devstoreaccount1;"

And you can check in the Service Bus queue by peeking messages from the start of the queue - you should see responses from both suppliers.

You can use your Service Bus namespace for the Azure deployment (or you might prefer to create new ones).

Deploy to Azure

Here’s the setup to get you started:

az group create -n labs-functions-servicebus --tags courselabs=azure -l eastus

az storage account create -g labs-functions-servicebus --sku Standard_LRS -l eastus -n <sa-name>

az functionapp create -g labs-functions-servicebus  --runtime dotnet --functions-version 4 --consumption-plan-location eastus --storage-account <sa-name> -n <function-name> 

The pre-reqs for your function are:

a service bus namespace with topic QuoteRequestTopic and two subscriptions Supplier1Subscription & Supplier2Subscription
the connection string for the for the Service Bus as appsetting ServiceBusInputConnectionString
a service bus queue with name QuoteStoredQueue
the connection string for the for the Service Bus as appsetting ServiceBusOutputConnectionString
a storage account for output
the connection string for the for the storage account as appsetting OutputTableStorageConnectionString

Then you’ll be ready to publish:

func azure functionapp publish <function-name>

Lab

You’d want to test this at scale. How could you use a Function to do that?

Stuck? Try suggestions.

Cleanup

Stop the Azure Storage emulator:

docker rm -f azurite

Delete the lab RG:

az group delete -y --no-wait -n labs-functions-servicebus

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