Service discovery does not refresh

[bart-vmware]

Is there an existing issue for this?

• [x] I have searched the existing issues

Describe the bug

I've implemented an IServiceEndpointProvider that doesn't use IChangeToken. I would expect that PopulateAsync is called periodically, based on ServiceDiscoveryOptions.RefreshPeriod, which is documented as:

Gets or sets the period between polling attempts for providers which do not support refresh notifications via IChangeToken.ActiveChangeCallbacks.

However, no refresh ever happens. The reason is because ServiceEndpointWatcher never schedules the refresh timer when any of the providers (so not mine) added a change token:

// Check if we need to poll for updates or if we can register for change notification callbacks.
if (endpoints.ChangeToken.ActiveChangeCallbacks)
{
    // Initiate a background refresh when the change token fires.
    _changeTokenRegistration = endpoints.ChangeToken.RegisterChangeCallback(
        static state => _ = ((ServiceEndpointWatcher)state!).RefreshAsync(force: false), this);

    // Dispose the existing timer, if any, since we are reliant on change tokens for updates.
    _pollingTimer?.Dispose();
    _pollingTimer = null;
}
else
{
    SchedulePollingTimer();
}

Because the configuration provider is added from builder.Services.AddServiceDiscovery() which is invoked from the ServiceDefaults project, there will always be a change token after ServiceEndpointWatcher has enumerated all providers.

Does this work as designed and is the documentation wrong, or is this a bug?

Expected Behavior

Documented behavior to match with the implementation.

Steps To Reproduce

• Create a new Aspire Starter project without output caching
• Implement IServiceEndpointProviderFactory / IServiceEndpointProvider
• Write a log line from IServiceEndpointProvider.PopulateAsync
• Add the factory to the service collection at startup, and configure RefreshPeriod to 1 second
• Hit the weather endpoint in the browser a few times and check the logs

Exceptions (if any)

.NET Version info

.NET 8

Anything else?

No response

[bart-vmware]

/cc @ReubenBond