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.

Schweiker

Did you already take a look at cubeslam source repository? It sounds that a third approach: RTCDataChannel+STUN server running on Compute, could also work for you. – Cocker

Also note that as of today neither Compute Engine or App Engine have "zone" in Asia. – Cocker

Do you have any server side logic that you need to run or do you only need to be broadcast packet between client? – Cocker

Are all the player potentially sending events to each other? Or are they grouped by a logical unit, affinity, location? – Cocker

Proppy, CubeSlam source repository is definitely an interesting reading ! Thank you for pointing this out. We could actually find some front side tricks to avoid server side processing. Any player would only connect to another player, so 2 players connected together, potentially from different world zone, no broadcasting and no grouping. (Added these clarifications on the question) – Schweiker

the same approach as CubeSlam could apply. For browser compatibility you might look at existing polyfill for WebRTC: github.com/ShareIt-project/DataChannel-polyfill – Cocker

You can also take a look at developers.google.com/drive/realtime which is useful for sharing state across multiple browser application. – Cocker

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.

Audwin

Thank you very much Alfred ! Indeed, Channel API latency can vary from ~150ms to up to 20secs ! convenient for many things, but pretty unreliable for "real" realtime needs. WebRTC definitely look like a great solution if we didn't care about supporting a wide range of browsers (only for Chrome and Firefox for now), and Proppy pointed out a good reading : CubeSlam source repository. Thanks again ! – Schweiker

The argument about WebRTC is not valid - it's kind of a chicken and egg problem when it comes to signaling and using WebRTC. To implement proper signaling (connecting peers that are geographically close and hold resources that are valid for sharing), you need exactly the same solution as you would need for a publisher/subscriber mechanism that you would probably want to implement using web sockets / comet / polling. – Belly

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.

Undertow

I think you mean "sockets" support for AppEngine, not WebSocket: developers.google.com/appengine/docs/java/sockets which is probably not a good fit here. – Rogue

Answer 3

Alfred's answer is the best in the frame of the question I asked. Thank you very much !

However, I forgot to mention a few important points and the scope changed a bit :

• We have very little development time (about 1 week only)
• This is for a campaign that will last 3 weeks only (we'll need to keep it online a few months afterward, but this is not like we need a long-lasting architecture)
• We need to make it work on the broader browser audience as possible (WebRTC only runs on Chrome & Firefox for now)

According to these points, we eventually came up to a 3rd solution :
Using a real-time PAAS.

It's way easier and faster to develop, way cheaper as we don't need a solid backend developer and system/network admin, and we can concentrate more on the project than on the infrastructure and platform.

There are a couple of services that seems good out there, already hosting MMO RPG and the kind, worldwide, with low latency, and good scaling systems.
Here is a list of providers :
https://github.com/leggetter/realtime-web-technologies-guide/blob/master/guide.md

Schweiker