title: how to send push notifications efficiently to selected users in an app?
body: <p>I'm trying to implement a push notification server using nodejs and websockets. The server i'm trying to implement needs to be able to send notifications that are specific to each user in the app(eg: person A commented on your post etc...). The server also can serve many apps. Therefore the number of users who use the service is very high. </p>
  
  <p>The problem is how can I manage the channels. I did some research on Internet and could not find a solid solution to this. 
  This <a href="https://stackoverflow.com/questions/12993099/websockets-correct-approach-for-creating-channels-and-pushing-data">question also</a> <a href="https://stackoverflow.com/questions/12993099/websockets-correct-approach-for-creating-channels-and-pushing-data">asks</a> something similar. But does not have solid answers.</p>
  
  <p>One way I thought of implementing this is to, have one channel per each user, then It may will not scale well to server many users.</p>
  
  <p>Another way I thought was to organize the same messages into groups and then creates channels for the groups. Then the downside is a logged in user will need to subscribe to multiple channels and also there could be many groups that contain only one user. On the other hand the grouping process also effect the efficiency.</p>
  
  <p>My question is what is/are the efficient methods to handle this problem. Can you please give me some insight into this? Any help is greatly appreciated. Thanks.</p>