Mongodb sort inner array

You can do this by $unwinding the updates array, sorting the resulting docs by date, and then $grouping them back together on _id using the sorted order.

db.servers.aggregate(
    {$unwind: '$service.apps.updates'}, 
    {$sort: {'service.apps.updates.date': 1}}, 
    {$group: {_id: '$_id', 'updates': {$push: '$service.apps.updates'}}}, 
    {$project: {'service.apps.updates': '$updates'}})