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Microsoft Azure Event Hub

Microsoft Azure implementations reside in a separate package NuGet

This package tries to abstract access to Azure Event Hubs and making them available as IMessagePublisher and IMessageReceiver.

Using

Publishing Messages

To publish a message first you need to create a publisher:

IMessagePublisher publisher = StorageFactory.Messages.AzureEventHubPublisher(
                  connectionString,
                  entityPath);

The connection string specifies a connection string to Event Hub Namespace and not a specific entity. The entity is passed as a second parameter, which is shown on a screenshot below:

Eh 00

Eh 01

If you need another way to connect to Event Hubs, please raise an issue in this project.

Receiving Messages

You can receive messages by creating an IMessageReceiver with the following factory method:

IMessageReceiver receiver = StorageFactory.Messages.AzureEventHubReceiver(
                  connectionString,
                  entityPath,
                  patitionIds,
                  consumerGroupName,
                  stateStorage);

connectionString and entityPath should match the publisher parameters, the rest of them need an explanation:

  • partitionIds is an optional parameter of IEnumerable<string> type and when specified creates a listener only for partition IDs passed. When ommitted, this receiver will listen on all partitions of Event Hub.
  • consumerGroupName is used to specify Event Hub consumer group and is also an optional parameter. When not set, a default consumer group is used which is always present in any Event Hub namespace. It is recommended to create a new consumer group for each physical application to prevent Event Hub locking as a general practice, especially if you have more than one application listening for messages on a single Event Hub namespace.
  • stateStorage is used to persist state of Event Hub partitions for an application. It's of type IBlobStorage and this library is using blobs to checkpoint partition state. In Microsoft's original Event Hub library you don't have a choice other than use Azure Blob Storage for checkpointing, however Storage.Net gives you a flexibility to pass any supported implementation of IBlobStorage. When not specified, Storage.Net will use a built-in in-memory provider, which means that your listener will start fetching all messages from Event Hub from the beginning of the history every time your application started. For this reason it's recommended to use someting more persistent than memory storage.

In this example we are using Azure Blob Storage for checkpointing just to showcase the syntax:

IMessageReceiver receiver = StorageFactory.Messages.AzureEventHubReceiver(
    connectionString,
    entityPath,
    null,
    null,
    StorageFactory.Blobs.AzureBlobStorage(
        storageName,
        storageKey,
        "eventhubcheckpoint"));

Appendix 1. Listing Event Hub Partitions

You can list available partitions of a specific Event Hub instance by casting IMessageReceiver to AzureEventHubReceiver class and invoking GetPartitionIds() method. Note that this is a leaky abstraction, however this is no generic way to list partitions because it really Event Hub specific. Use this code in configuration/initialisation logic, however I'd strongly discourage embedding this into application logic.