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Load Balanced Game Server on Google Compute Engine

Copyright

Copyright 2013 Google Inc. All Rights Reserved.

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.

Disclaimer

This sample application is not an official Google product.

Please note that if you are storing any user information in your application, you must comply with Google App Engine's & Google Compute Engine's Terms of Service item 4.2.

Google App Engine Terms of Service

https://developers.google.com/appengine/terms

Google Compute Engine Terms of Service

https://developers.google.com/compute/docs/terms

Summary

Sample application of App Engine that manages game server on Google Compute Engine.

This sample illustrates use of App Engine as management system of Google Compute Engine. By the combination of different technologies, it enables automatic scaling of Google Compute Engine instances.

This sample uses Grits as a game server example.

Setting Up the Sample

Directory Structure for Set Up

The following set up instruction assumes that we work on the directory where the sample applicaiton is retrieved/extracted. The final view of the directory will be as follows.

Current Directory
      |- solutions-load-balanced-gaming-server-on-google-compute-engine-master/
            |- static_files/
            |- worker/
      |- gritsgame/
      |- gritsgame.tar.gz
      |- google_appengine/
      |- google_appengine_1.7.5.zip
      |- google_appengine_1.7.5.tar.gz
      |- node-v0.10.0-linux-x64.tar.gz

Download Grits package

Grits is distributed here. Since Grits package is not necessary to App Engine application, it is recommended to create Grits package outside the sample application directory to avoid unnecessary file upload to App Engine.

git can be downloaded from here, or OS may provide easier way to install it.

git clone https://code.google.com/p/gritsgame/
(cd gritsgame; git checkout 4462f1dd8d87)

Patch Grits

We need slight modification to Grits so that both frontend and backend of grits work on the same Google Compute Engine instance. The sample application includes the patch file to apply to Grits package in solutions-load-balanced-gaming-server-on-google-compute-engine-master directory.

patch -p0 < solutions-load-balanced-gaming-server-on-google-compute-engine-master/gritsgame.patch
tar zcf gritsgame.tar.gz gritsgame

Download App Engine and Node.js packages

Download App Engine SDK and Node.js. They are required to run Grits on Google Compute Engine. These packages can be downloaded to the same directory as the sample is uncompressed, where gritsgame.tar.gz is generated in the previous step. The files may be downloaded by Web browser, or the download can be performed by the following commands. If the system doesn't have wget, curl command can be used with -O option instead, as curl -O <URL>.

wget http://googleappengine.googlecode.com/files/google_appengine_1.7.5.zip
wget http://nodejs.org/dist/v0.10.0/node-v0.10.0-linux-x64.tar.gz

Note the sample uses App Engine development server as Grits game server platform on Google Compute Engine instances. The SDK package is not relevant to the main App Engine application, but the sample requires App Engine SDK installed on the development environment. Also note App Engine 1.7.6 (or later) is not compatible with Grits game server. Since App Engine SDK on the development environment and one on Google Compute Engine is not relevant, it's fine to have different versions for them.

App Engine SDK must be repackaged to gzipped tar file before the package is uploaded to the Google Cloud Storage.

unzip -q google_appengine_1.7.5.zip
tar zcf google_appengine_1.7.5.tar.gz google_appengine

Prepare Google Cloud Storage

Create Google Cloud Storage bucket and upload Grits, App Engine and Node.js packages there. Google Compute Engine instances will download these packages from the bucket, and install them.

You can either:

Upload packages to the Google Cloud Storage bucket.

gsutil -m cp gritsgame.tar.gz  \
             google_appengine_1.7.5.tar.gz  \
             node-v0.10.0-linux-x64.tar.gz  \
             gs://<bucket name>

Modify Sample Application for your Project and Google Cloud Storage Bucket

Replace bucket name in compute_engine_controller.py in the sample application. Change value of CLOUD_STORAGE_DIR class variable of ComputeEngineController. Also set the right PROJECT_ID. Project ID is found on "Overview" tab of Google APIs Console.

PROJECT_ID = '{{{{ project_id }}}}'
CLOUD_STORAGE_DIR = 'gs://{{{{ bucket }}}}'

Google Compute Engine Instance Parameters

The sample application uses us-central1-a and n1-standard-1 instance type. The parameters can be changed by modifying value of DEFAULT_ZONE and DEFAULT_MACHINE_TYPE variables in compute_engine_controller.py.

Prepare App Engine application

Create new App Engine application on appspot.com from App Engine console.

Since Game Server needs to communicate with App Engine application, make sure to create an application where authentication is not required, such as one on appspot.com.

Also the application should be accessible by everybody. When you choose Authentication Options, make sure to select "Open to all Google Accounts users". This authentication method without access restriction makes the application public to everybody.

Fill application ID just created in app.yaml.

application: {{{{ app_id }}}}

Create client ID and client secret

Client ID and client secret are required by OAuth2 authorization to identify the sample application. It is required in order for the application to access Google API (in this example, Google Compute Engine API) on behalf of the user.

Client ID and client secret can be set up from API Access page of Google APIs Console.

Choose "Web Application" as application type. Set redirect URIs to http://<application ID>.appspot.com/oauth2callback.

Replace client_id and client_secret values in the parameter list of OAuth2Decorator in handlers.py with the actual values from Google APIs Console.

client_id = '{{{{ client_id }}}}',
client_secret = '{{{{ client_secret }}}}',

Google Client API

Google Client API is library to access various Google's services via API. This sample uses the library to access Google Compute Engine.

Download google-api-python-client-gae-1.1.zip from download page, or download by command line.

wget http://google-api-python-client.googlecode.com/files/google-api-python-client-gae-1.1.zip

Set up the library in the sample application root directory.

(cd solutions-load-balanced-gaming-server-on-google-compute-engine-master; unzip ../google-api-python-client-gae-1.1.zip)

Set up Firewall on Google Compute Engine Network

Grits requires direct access from browser to the Google Compute Engine instance where the game server runs. The firewall rule must be added to allow access to TCP port 8000 to 20000 range. The firewall can be created from "Networks" menu of Google Compute Engine Web UI. The firewall may also be created by the following command.

gcutil addfirewall --project <project name> --allowed tcp:8000-20000 gritsgame

Deploy

The sample application can be deployed to App Engine now. The deployment is done by App Engine Launcher, or by appcfg.py command included in App Engine SDK.

appcfg.py [--oauth2] update solutions-load-balanced-gaming-server-on-google-compute-engine-master

Verification

http://<application ID>.appspot.com/ shows user's page to choose game server to log in (or let App Engine choose one by "Quick Game"). http://<application ID>.appspot.com/stats (also linked from the top page) requires administrator log in, and enables to start and shut down game server cluster.

Before starting the game, the game server cluster must be started from stats page. Until game servers are started and warmed up, "Quick Game" from the top page fails. When game servers are listed on the top page, user can choose which game server to log in, or "Quick Game" automatically chooses one of the game servers with low resource usage.

In this sample, each Grits game server can host up to 8 players. Therefore, one player is translated to 12.5% of the resource of the instance.

stats page allows administrator to simulate high-load condition. Artificial resource usage percentage can be set (and reset) for each game server. Set resource usage high, so that average usage is >80%. App Engine cron task checks the average resource usage of all instances every minute. If the resource usage is >80%, the App Engine cron task automatically spins up more Google Compute Engine instances, to keep the average resource usage low.