Playground - how does AspireEventHub connect to storage for checkpoints?

[christiannagel]

The playground for Azure Event Hub https://github.com/dotnet/aspire/tree/main/playground/AspireEventHub uses Azure Storage for checkpoints:

AppHost/Program.cs:

var blob = builder.AddAzureStorage("ehstorage")
    .AddBlobs("checkpoints");

var eventHub = builder.AddAzureEventHubs("eventhubns")
    .AddEventHub("hub");

builder.AddProject<Projects.EventHubsConsumer>("consumer")
    .WithReference(eventHub)
    .WithReference(blob);

With a previous version, the storage account was connected with the settings of event processor client configuration:

EventHubsConsumer/Program.cs:

    builder.AddAzureEventProcessorClient("eventhubns",
        settings =>
        {
            settings.EventHubName = "hub";
            settings.BlobClientConnectionName = "checkpoints";
        });
    builder.Services.AddHostedService<Processor>();
    Console.WriteLine("Starting EventProcessorClient...");

This is no longer the case with the new version:

EventHubsConsumer/Program.cs:

    builder.AddAzureBlobClient("checkpoints");

    builder.AddAzureEventProcessorClient("eventhubns",
        settings =>
        {
            settings.EventHubName = "hub";
        });

I couldn't find where the connection between the hub and storage is now.

From this pull request #3293 I've seen

The BlobServiceClient is first looked for as a keyed service using settings.BlobConnectionName -- the serviceKey is always the same as the connectionName for keyed services. If this is not found, a default service is looked for. If this is not found, an InvalidOperationException is thrown with a helpful message. This is a breaking change from Preview 5.

The BlobConnectionName is not set with the event processor client settings anymore. Is it now configured as default service?

Thanks for implementing this component @oising :-) I just need it for the current chapter I'm working on.

[oising]

Hi Christian -- simply put, the EventProcessorClient component will now look for a BlobServiceClient in the default (non-keyed) DI container, and then create a BlobContainerClient from it for the checkpointing. If it doesn't find one, it will now throw an InvalidOperationException with a hint about the problem. I agree it's less explicit and more magical in p5, but if you want more explicit behaviour, add a keyed blob client component using AddKeyedAzureBlobClient and then you'll have to provide the BlobClientServiceKey name on the EH client settings to match the keyed service name.

[oising]

yeah, I think the PR description is a little out of sync with the contents because Microsoft made a few changes, notably renaming BlobConnectionName to BlobClientServiceKey (iirc)