how to build a presence system with the new firebase queue - firebase

Question

I have a chat application using firebase and node.js where I keep track of presence by running a single worker thread on the server that monitors child_added and child_deleted events on the firebase presence channel, and updating our presence database tables accordingly.
My question is this - now that firebase queue exists https://www.firebase.com/blog/2015-05-15-introducing-firebase-queue.html
Can I use the queue to replace the worker thread that I have running on the server to monitor presence and child_added events? Looking at the current examples - it looks like I would create a reference to the queue on the client and then set on disconnect and connect events to push into that queue from the client? However I'd like to secure it a bit more and not rely on the client so much. I'd also like to have the queue process the event by archiving it to a 3rd party logging service - credentials or details I wouldn't want to expose to the client.
Does this mean I would still need a server side worker process - and if so what benefit would the firebase queue be in this use case?

Answer 1

Firebase Queue is not a hosted solution - you still need to run it on your own server.
The main advantage of using a queue over a single listener process is the ability to run multiple workers for the same tasks so there's not a single point of failure. Using the queue you'll know that the worker processes are synchronized such that only one worker will be processing a task at any one point in time, and if a worker dies during processing or takes too long, another worker will pick it up again once the task has timed out.
It sounds like you're trying to create some kind of audit trail for presence, but there's currently no way to report presence directly from the server - you'll need to rely on the client at some point. Your security rules can enforce whether a write is a boolean to specific location in your database, but they can't enforce that the client was in any particular presence state when writing it. Also note that there's no push or childByAutoId equivalent onDisconnect handler, so to push to a queue you'd have to do something like:
var ref = new Firebase(…);
var disconnectTask = {};
var pushId = ref.push().key(); // This just generates the ID and does no network traffic
disconnectTask[pushId] = { /* populate with task data here */ };
ref.onDisconnect().update(disconnectTask);
Note that the push ID will be generated client-side before the operation is sent to the server and so the task won't necessarily be in order when added to the queue.