Keeping iOS app in sync with server

Question

We are designing a system that based on particular events on the server creates geofences for particular device. It is expected that the client (device) will be in sync with the server data, question is how?

Initial (most optimal) idea was to send a silent push to the device to notify it about new data, and trigger data pull. Knowing that this solution will work for Android OS devices, we though the problem can be solved in similar fashion on iOS. Unfortunately, my iOS dev told me that silent push are not reliable on iOS, and presented following discussion: Silent push notifications only delivered if device is charging and/or app is foreground.

Therefore, my question is how to keep the (geofence) data on the iOS devices in sync with server side?

• We can pull, say every say 5 minutes, this solution is extremely inefficient, for most of the devices new geofences are changed rarely if at all, but our ‘power users’ need to have geofences updated very often.
• We could push with some kind of silent push mechanism, but it has to be reliable.
• Maybe some kind of persistent connection (tcp or better udp) but that seems like battery draining solution. Besides not reliable, the server would have to keep track of changing IPs which is not even possible on many cellular networks.
• WebSocket. Also battery draining solution, that is not intended for background sync. Overkill for devices that really have the data updated rarely (like once a month).
• Some commercial solution (PubNub or Pusher), but we would definitely prefer in house solution.

Are there any other solutions that are used in such cases? Maybe our approach with silent push is not right, but there is other build in Apple solution for such use case?

Answer 1

There's a fantastic service called Simperium with an iOS SDK that can help keep your info in Sync. I heard about them because I started using SimpleNote, a free note-taking tool that uses the sync service. They were acquired by Automattic, which runs Wordpress so the whole deal should be decently stable.

Hope this helps!

Answer 2

I'm not sure how much data you are working with but having a REST query every 5 mins is the way I'd go. Perhaps you can even switch it to a query each time you start up the app would be good enough?

We have an app where the user data needs to be sync'd with the back end server - each time we start the app it queries the backend server to see if there are any updates. We md5hash the data from the server and then we can just check our hash against the latest data - if it doesn't "match" then we pull the new data set.

In general, iOS doesn't really allow you to do multi-tasking the way you can do on android. Now, if you aren't releasing to the app store - and only using this as an in-house app you can get a little funky with things and run in a background mode.

Answer 3

You can run your syncing operations in the applicationDidEnterBackground: method within AppDelegate. That's the solution I've always used as long as the syncing operation doesn't take too long.

Here you can also query your database for data changes instead of pushing a trigger to the device, which could get hairy with push notifications and aren't really their intended use. If changes in the data are found (or some boolean flag is checked) then initiate a data pull.