Realtime game on Google Cloud : Channel API or Compute Engine?

Question

We need to develop a multi-player game with real-time performance. This needs to be working worldwide (servers in America, Europe, Asia), and supporting a huge traffic. Using Google Cloud services for the hosting.

We're thinking of references like Jam with Chrome, Chrome Maze or Cube Slam.

The game :

• 2 players challenge a race
• We need to simultaneously display the progression of the 2 players
• Each match could last around 30 to 45 seconds

The hosting :

We will obviously host the website on AppEngine, automagically scaling, but are thinking about 2 solutions for the real-time servers :

1. Using websocket servers with Compute Engine
   
   Like they did for Jam with Chrome, Maze, etc.
   Developing our own websocket servers (technology TBD), deploying on datacenters in Europe, US, Asia, handling scaling, syncing between them, computing latency issues on servers and clients, etc.
   But it's pretty technically challenging as we are very short on time, and missing an admin sys and network guy for now.

2. Or using Channel API
   
   We understand that it's not a websocket platform, and real-time performances are lower.
   But it would be way more simple and secure for us and the time we have.
   So, we would also like to know more about that.

In any case, we think we could use some graphical tricks on front ends, to make it look like real-time, but it really depends if we have a 100~500ms or a 500ms~10s latency.

Some questions :

• What would the latency range values look like for the different solutions ?
  (Jam w/ Chrome got 100ms with GCE, could Channel API reach several seconds ?)
• How would Channel API servers handle high traffic, how does scaling work, could the latency go very high ? (no info about that on Channel docs ?)
• What if someone in France play with someone in US, connecting to different servers, waiting them to sync, how to deal with it ?
• Any advice or experience to share ?
• Any interesting reading or viewing ? (seen some but not very precise)
• Any other solution ?

Thank you for any helping comment !

EDIT :

• Only 2 players connected together, potentially from different world zone, no broadcasting needed.
• We could find some front side tricks to avoid server side processing. This is a race between 2 players, so we actually just need to compare their progression, and the real winner resolution is not that important as there is no real stuff to win, this is more for fun.

Answer 1

If you need a server for processing the data:

I would definitely go with websockets at Compute Engine!

The Channels API is much slower, and also quite unpredictable (latency differs from message to message)! Data has to go to the Channels server, which sends it to the App Engine instance, which has to do a request back to the Channels server, which will push the message to the client. There is too much going on there if you want to keep latency down!

Here is a Channels API stress test:
http://channelapistresstest.appspot.com/
Try clicking "send 5"-button a lot, and you will see latency numbers going up to several seconds.

The Channels API is also quite expensive under heavy load (it probably does not scale well, even if Google of course can solve that with more instances).

When keeping latency down, geolocation is quite important. With a websocket server at Compute Engine, you can send your european visitors to google's european datacenter and your american visitors to the US datacenter (using the geo location headers that AppEngine will provide). You have no such control with the Channels API (or app engine, which all your messages are relayed through). Maybe Google has edge servers for the Channels API (I don't know), but if your AppEngine instance is on the other side of the planet, that does not matter.

If you do NOT need a server for processing the data:

You should establish a peer-to-peer connection with WebRTC, sending stuff directly between the users' browsers. That is was Cube Slam does. (WebRTC requires some initial handshaking ("signaling") so the two peers can find each other, and Channels API would work fine for that handshaking, that's just a couple of messages to establish the peer-to-peer connection.)

WebRTC DataChannels API will give you a nice websocket-like interface like channel.onmessage = function(e) { yadayada()... }; and channel.send("yadayada"); to send your data between the peers.

Occasionally, WebRTC is not able to make a peer-to-peer connection. Then it will fall back to a TURN server, which relays traffic between the peers. Cube Slam is using TURN servers running on ComputeEngine (in both Europe and America to keep latency down), but that is just the fallback when true peer-to-peer is not possible.

Answer 2

It also depends on other things like scalability.

Ingress is built on app engine and a part from the occasional cache glitch it is pretty impressive.

Remember that the channel api is using talk.Google which is the service that hangouts is built on. Scalable and real time.

Personally if your traffic levels are going to be erratic and unpredictable, go app engine. If you think it can be controlled and predictable use compute engine or something else.