I have an application in which I am sending push notifications to iOS devices using AWS SNS. My application reports that 100% of the notifications are being successfully added AWS SNS. However, when I look at my cloud watch metrics in the AWS dashboard, a number of messages aren't being delivered, there is no discernible pattern.
I have done testing by sending requests to my server via curl, the server reports back success, I then can watch the notification come in to my iPhone. If I send 4 - 6 requests in a row, over the span of about 10 seconds, only about 3 messages actually get delivered. If I wait for a couple of seconds after the failures, then I can repeat this same behavior.
I have also observed a strange behavior where notifications will not be delivered, but periodically, it seems that a single message will force through all of the undelivered messages and I'll get a flood of notifications.
What in the world is going on here, is this an AWS problem? Have other people been experiencing this with SNS?
Update June 18, 2014
I am working on another project now using NodeJS, so I am using the JavaScript AWS SDK. This post originally was about a project using the PHP AWS SDK. I haven't really seen the behavior described above while using the JavaScript AWS SDK.