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Publish-Subscribe with Event Hubs on Dapr

This solution demonstrates how to consume messages from a message broker with the Dapr pub-sub component using Node.js, Go and C#.

The accompanying blog post goes through the configuration steps and considerations when choosing Azure Event Hubs as the message broker. However, the code for consuming the messages does not change if a different message broker is selected, only the component YAML file.

Blog post: https://madeofstrings.com/2020/07/05/pub-sub-with-dapr-and-azure-event-hubs/

At a high-level, the physical architecture for this solution looks like:

Physical architecture

Setup with Azure Cloud Shell for Azure Event Hubs

Initialize variables

# resource group name and location
rgname=zohan-dapr-demo
location=westus2

# event hubs namespace and event hub (topic)
ehnamespace=<unique-event-hubs-namespace-name>
ehname=songs

# authorization rule for shared access policy
authorizationrule=authorizationpolicy

# consumer group for each subscriber
consumergroup1=csharp-subscriber-app
consumergroup2=node-subscriber-app
consumergroup3=go-subscriber-app

# storage account name
storageaccount=<unique-storage-account-name>

Create Event Hubs and Event Hub (topic)

# create event hubs namespace
az eventhubs namespace create --name $ehnamespace -g $rgname -l $location --sku Standard

# create event hub (topic)
az eventhubs eventhub create -g $rgname --namespace-name $ehnamespace --name $ehname

Create consumer groups, one for each subscriber

# csharp subscriber
az eventhubs eventhub consumer-group create --resource-group $rgname --namespace-name $ehnamespace --eventhub-name $ehname --name $consumergroup1

# node subscriber
az eventhubs eventhub consumer-group create --resource-group $rgname --namespace-name $ehnamespace --eventhub-name $ehname --name $consumergroup2

# go subscriber
az eventhubs eventhub consumer-group create --resource-group $rgname --namespace-name $ehnamespace --eventhub-name $ehname --name $consumergroup3

Create a shared access policy

# create shared access policy with send and listen rights
az eventhubs eventhub authorization-rule create --eventhub-name $ehname --name $authorizationrule --namespace-name $ehnamespace -g $rgname --rights Send Listen

# query the primary connection string
az eventhubs eventhub authorization-rule keys list --resource-group $rgname --namespace-name $ehnamespace --eventhub-name $ehname --name $authorizationrule --query "primaryConnectionString"

Create a storage account

# create storage account
az storage account create --name $storageaccount --location $location --resource-group $rgname --sku Standard_LRS --kind BlobStorage --access-tier Hot

Event Hubs pub-sub component

Important component details:

  • A different component must be used for each topic subscription.
  • The storage container name must match the name of consumer group for the subscription. For example, the storage account name for the Node.js application should be node-subscriber-app.

Here is an example of the component configuration for the Node application:

apiVersion: dapr.io/v1alpha1
kind: Component
metadata:
  name: messagebus-node
spec:
  type: pubsub.azure.eventhubs
  version: v1
  metadata:
    - name: connectionString
      value: Endpoint=sb://<namespace-name>.servicebus.windows.net/;SharedAccessKeyName=<policy-name>;SharedAccessKey=<key>;EntityPath=<event-hub-name>
    - name: storageAccountName
      value: <storage-account-name>
    - name: storageAccountKey
      value: <storage-account-key>
    - name: storageContainerName
      value: node-subscriber-app