Azure Notification Hub - do installations prevent duplicate notifications?

Question

In the article describing the registration management it states that:

The following are some key advantages to using installations:

Creating or updating an installation is fully idempotent. So you can retry it without any concerns about duplicate registrations

What does it exactly mean? I assume it doesn't mean the installations have a 'CreateOrUpdate' unlike registrations, because a similar method also exists there - 'CreateOrUpdateRegistrationAsync'.

Suppose that I've created two installations with different installation ID but the same PNS handle (pushChannel property) and identical tag 'foo' present in both installations. I'm going to send a notification using the SendTemplateNotificationAsync method using the 'foo' tag to select the target of my notification.

It's going to match both my installations, because they both contain the tag 'foo' and both have the same PNS handle. Is the device going to receive two notifications, or is Azure going to prevent delivery of duplicates in this case?

In the the same article I've linked the code samples do check for existing registrations with the PNS handle that's about to get registered:

// make sure there are no existing registrations for this push handle (used for iOS and Android)    
    string newRegistrationId = null;
    var registrations = await hub.GetRegistrationsByChannelAsync(pushChannel.Uri, 100);

but they don't check that in the installations samples, which again suggests that Azure prevents delivery of duplicate notifications.

RKalra RKalra · Accepted Answer · 2019-04-10T17:33:42

Creating or updating an installation is fully idempotent. So you can retry it without any concerns about duplicate registrations

Here, an installation is a term used to describe an enhanced registration (with Azure's Notification Hub) to associate PNS of the device with tag(s) and/or template(s). "Idempotency" here is used with regards to the act of such an installation.
What it means is that you can simply call the same code for this type of registration every time your app starts or is brought to foreground without worrying about handling changes in PNS or previous states of registration with the Notification Hub.
This is good because the classic registration model can lead to duplicate registrations for the same device and user in the notification hub. Installation model doesn't do that.

Q. What would happen when you have one PNS assigned to multiple registrations with same tag in the Notification Hub and you try to push a notification by targeting a tag?
A. Azure Notification Hub has de-duplication logic which will prevent duplicate notifications from going out.

Q. Can you force multiple notifications (for the same tag) in any way if you have multiple applications but one Notification Hub?
A. You can if you can get multiple device tokens. However, in case of iOS, as APNS issues only one valid device token at a time, it will not be possible. Also, iOS apps have their own bundle identifier and therefore their own specific push certificate. And, Notification Hubs don't support multiple certificates. But in case of Android, you can force it if you use registration model and use older GCM registration Ids as they are renewed frequently and don't expire so easily.

Hope that helps! Cheers!

Azure Notification Hub - do installations prevent duplicate notifications?

1 Answers