@aws-cdk/aws-gamelift-alpha module

Language	Package
.NET	Amazon.CDK.AWS.GameLift.Alpha
Go	github.com/aws/aws-cdk-go/awscdkgameliftalpha/v2
Java	software.amazon.awscdk.services.gamelift.alpha
Python	aws_cdk.aws_gamelift_alpha
TypeScript	@aws-cdk/aws-gamelift-alpha

Amazon GameLift Construct Library

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The APIs of higher level constructs in this module are experimental and under active development. They are subject to non-backward compatible changes or removal in any future version. These are not subject to the Semantic Versioning model and breaking changes will be announced in the release notes. This means that while you may use them, you may need to update your source code when upgrading to a newer version of this package.

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Amazon GameLift is a service used to deploy, operate, and scale dedicated, low-cost servers in the cloud for session-based multiplayer games. Built on AWS global computing infrastructure, GameLift helps deliver high-performance, high-reliability game servers while dynamically scaling your resource usage to meet worldwide player demand.

GameLift is composed of three main components:

• GameLift FlexMatch which is a customizable matchmaking service for multiplayer games. With FlexMatch, you can build a custom set of rules that defines what a multiplayer match looks like for your game, and determines how to evaluate and select compatible players for each match. You can also customize key aspects of the matchmaking process to fit your game, including fine-tuning the matching algorithm.

• GameLift hosting for custom or realtime servers which helps you deploy, operate, and scale dedicated game servers. It regulates the resources needed to host games, finds available game servers to host new game sessions, and puts players into games.

• GameLift FleetIQ to optimize the use of low-cost Amazon Elastic Compute Cloud (Amazon EC2) Spot Instances for cloud-based game hosting. With GameLift FleetIQ, you can work directly with your hosting resources in Amazon EC2 and Amazon EC2 Auto Scaling while taking advantage of GameLift optimizations to deliver inexpensive, resilient game hosting for your players

This module is part of the AWS Cloud Development Kit project. It allows you to define components for your matchmaking configuration or game server fleet management system.

GameLift FlexMatch

Defining a Matchmaking configuration

FlexMatch is available both as a GameLift game hosting solution (including Realtime Servers) and as a standalone matchmaking service. To set up a FlexMatch matchmaker to process matchmaking requests, you have to create a matchmaking configuration based on a RuleSet.

More details about matchmaking ruleSet are covered below.

There is two types of Matchmaking configuration:

Through a game session queue system to let FlexMatch forms matches and uses the specified GameLift queue to start a game session for the match.

declare const queue: gamelift.GameSessionQueue;
declare const ruleSet: gamelift.MatchmakingRuleSet;

new gamelift.QueuedMatchmakingConfiguration(this, 'QueuedMatchmakingConfiguration', {
  matchmakingConfigurationName: 'test-queued-config-name',
  gameSessionQueues: [queue],
  ruleSet: ruleSet,
});

Example not in your language?

Or through a standalone version to let FlexMatch forms matches and returns match information in an event.

declare const ruleSet: gamelift.MatchmakingRuleSet;

new gamelift.StandaloneMatchmakingConfiguration(this, 'StandaloneMatchmaking', {
  matchmakingConfigurationName: 'test-standalone-config-name',
  ruleSet: ruleSet,
});

Example not in your language?

More details about Game session queue are covered below.

Matchmaking RuleSet

Every FlexMatch matchmaker must have a rule set. The rule set determines the two key elements of a match: your game's team structure and size, and how to group players together for the best possible match.

For example, a rule set might describe a match like this: Create a match with two teams of four to eight players each, one team is the cowboy and the other team the aliens. A team can have novice and experienced players, but the average skill of the two teams must be within 10 points of each other. If no match is made after 30 seconds, gradually relax the skill requirements.

new gamelift.MatchmakingRuleSet(this, 'RuleSet', {
  matchmakingRuleSetName: 'my-test-ruleset',
  content: gamelift.RuleSetContent.fromJsonFile(path.join(__dirname, 'my-ruleset', 'ruleset.json')),
});

Example not in your language?

FlexMatch Monitoring

You can monitor GameLift FlexMatch activity for matchmaking configurations and matchmaking rules using Amazon CloudWatch. These statistics are used to provide a historical perspective on how your Gamelift FlexMatch solution is performing.

FlexMatch Metrics

GameLift FlexMatch sends metrics to CloudWatch so that you can collect and analyze the activity of your matchmaking solution, including match acceptance workflow, ticket consumtion.

You can then use CloudWatch alarms to alert you, for example, when matches has been rejected (potential matches that were rejected by at least one player since the last report) exceed a certain thresold which could means that you may have an issue in your matchmaking rules.

CDK provides methods for accessing GameLift FlexMatch metrics with default configuration, such as metricRuleEvaluationsPassed, or metricRuleEvaluationsFailed (see IMatchmakingRuleSet for a full list). CDK also provides a generic metric method that can be used to produce metric configurations for any metric provided by GameLift FlexMatch; the configurations are pre-populated with the correct dimensions for the matchmaking configuration.

declare const matchmakingRuleSet: gamelift.MatchmakingRuleSet;
// Alarm that triggers when the per-second average of not placed matches exceed 10%
const ruleEvaluationRatio = new cloudwatch.MathExpression({
  expression: '1 - (ruleEvaluationsPassed / ruleEvaluationsFailed)',
  usingMetrics: {
    ruleEvaluationsPassed: matchmakingRuleSet.metricRuleEvaluationsPassed({ statistic: cloudwatch.Statistic.SUM }),
    ruleEvaluationsFailed: matchmakingRuleSet.metric('ruleEvaluationsFailed'),
  },
});
new cloudwatch.Alarm(this, 'Alarm', {
  metric: ruleEvaluationRatio,
  threshold: 0.1,
  evaluationPeriods: 3,
});

Example not in your language?

See: Monitoring Using CloudWatch Metrics in the Amazon GameLift Developer Guide.

GameLift Hosting

Uploading builds and scripts to GameLift

Before deploying your GameLift-enabled multiplayer game servers for hosting with the GameLift service, you need to upload your game server files. This section provides guidance on preparing and uploading custom game server build files or Realtime Servers server script files. When you upload files, you create a GameLift build or script resource, which you then deploy on fleets of hosting resources.

To troubleshoot fleet activation problems related to the server script, see Debug GameLift fleet issues.

Upload a custom server build to GameLift

Before uploading your configured game server to GameLift for hosting, package the game build files into a build directory. This directory must include all components required to run your game servers and host game sessions, including the following:

• Game server binaries – The binary files required to run the game server. A build can include binaries for multiple game servers built to run on the same platform. For a list of supported platforms, see Download Amazon GameLift SDKs.

• Dependencies – Any dependent files that your game server executables require to run. Examples include assets, configuration files, and dependent libraries.

• Install script – A script file to handle tasks that are required to fully install your game build on GameLift hosting servers. Place this file at the root of the build directory. GameLift runs the install script as part of fleet creation.

You can set up any application in your build, including your install script, to access your resources securely on other AWS services.

declare const bucket: s3.Bucket;
const build = new gamelift.Build(this, 'Build', {
  content: gamelift.Content.fromBucket(bucket, "sample-asset-key")
});

new CfnOutput(this, 'BuildArn', { value: build.buildArn });
new CfnOutput(this, 'BuildId', { value: build.buildId });

Example not in your language?

To specify a server SDK version you used when integrating your game server build with Amazon GameLift use the serverSdkVersion parameter:

See Integrate games with custom game servers for more details.

declare const bucket: s3.Bucket;
const build = new gamelift.Build(this, 'Build', {
  content: gamelift.Content.fromBucket(bucket, "sample-asset-key"),
  serverSdkVersion: '5.0.0',
});

Example not in your language?

Upload a realtime server Script

Your server script can include one or more files combined into a single .zip file for uploading. The .zip file must contain all files that your script needs to run.

You can store your zipped script files in either a local file directory or in an Amazon Simple Storage Service (Amazon S3) bucket or defines a directory asset which is archived as a .zip file and uploaded to S3 during deployment.

After you create the script resource, GameLift deploys the script with a new Realtime Servers fleet. GameLift installs your server script onto each instance in the fleet, placing the script files in /local/game.

declare const bucket: s3.Bucket;
new gamelift.Script(this, 'Script', {
  content: gamelift.Content.fromBucket(bucket, "sample-asset-key")
});

Example not in your language?

Defining a GameLift Fleet

Creating a custom game server fleet

Your uploaded game servers are hosted on GameLift virtual computing resources, called instances. You set up your hosting resources by creating a fleet of instances and deploying them to run your game servers. You can design a fleet to fit your game's needs.

new gamelift.BuildFleet(this, 'Game server fleet', {
  fleetName: 'test-fleet',
  content: gamelift.Build.fromAsset(this, 'Build', path.join(__dirname, 'CustomerGameServer')),
  instanceType: ec2.InstanceType.of(ec2.InstanceClass.C4, ec2.InstanceSize.LARGE),
  runtimeConfiguration: {
    serverProcesses: [{
      launchPath: 'test-launch-path',
    }],
  },
});

Example not in your language?

Managing game servers launch configuration

GameLift uses a fleet's runtime configuration to determine the type and number of processes to run on each instance in the fleet. At a minimum, a runtime configuration contains one server process configuration that represents one game server executable. You can also define additional server process configurations to run other types of processes related to your game. Each server process configuration contains the following information:

• The file name and path of an executable in your game build.

• Optionally Parameters to pass to the process on launch.

• The number of processes to run concurrently.

A GameLift instance is limited to 50 processes running concurrently.

declare const build: gamelift.Build;
// Server processes can be delcared in a declarative way through the constructor
const fleet = new gamelift.BuildFleet(this, 'Game server fleet', {
  fleetName: 'test-fleet',
  content: build,
  instanceType: ec2.InstanceType.of(ec2.InstanceClass.C4, ec2.InstanceSize.LARGE),
  runtimeConfiguration: {
    serverProcesses: [{
      launchPath: '/local/game/GameLiftExampleServer.x86_64',
      parameters: '-logFile /local/game/logs/myserver1935.log -port 1935',
      concurrentExecutions: 100,
    }]
  }
});

Example not in your language?

See Managing how game servers are launched for hosting in the Amazon GameLift Developer Guide.

Defining an instance type

GameLift uses Amazon Elastic Compute Cloud (Amazon EC2) resources, called instances, to deploy your game servers and host game sessions for your players. When setting up a new fleet, you decide what type of instances your game needs and how to run game server processes on them (using a runtime configuration). All instances in a fleet use the same type of resources and the same runtime configuration. You can edit a fleet's runtime configuration and other fleet properties, but the type of resources cannot be changed.

declare const build: gamelift.Build;
new gamelift.BuildFleet(this, 'Game server fleet', {
  fleetName: 'test-fleet',
  content: build,
  instanceType: ec2.InstanceType.of(ec2.InstanceClass.C5, ec2.InstanceSize.LARGE),
  runtimeConfiguration: {
    serverProcesses: [{
      launchPath: '/local/game/GameLiftExampleServer.x86_64',
    }]
  }
});

Example not in your language?

Using Spot instances

When setting up your hosting resources, you have the option of using Spot Instances, On-Demand Instances, or a combination.

By default, fleet are using on demand capacity.

declare const build: gamelift.Build;
new gamelift.BuildFleet(this, 'Game server fleet', {
  fleetName: 'test-fleet',
  content: build,
  instanceType: ec2.InstanceType.of(ec2.InstanceClass.C4, ec2.InstanceSize.LARGE),
  runtimeConfiguration: {
    serverProcesses: [{
      launchPath: '/local/game/GameLiftExampleServer.x86_64',
    }]
  },
  useSpot: true
});

Example not in your language?

Allowing Ingress traffic

The allowed IP address ranges and port settings that allow inbound traffic to access game sessions on this fleet.

New game sessions are assigned an IP address/port number combination, which must fall into the fleet's allowed ranges. Fleets with custom game builds must have permissions explicitly set. For Realtime Servers fleets, GameLift automatically opens two port ranges, one for TCP messaging and one for UDP.

declare const build: gamelift.Build;

const fleet = new gamelift.BuildFleet(this, 'Game server fleet', {
  fleetName: 'test-fleet',
  content: build,
  instanceType: ec2.InstanceType.of(ec2.InstanceClass.C4, ec2.InstanceSize.LARGE),
  runtimeConfiguration: {
    serverProcesses: [{
      launchPath: '/local/game/GameLiftExampleServer.x86_64',
    }]
  },
  ingressRules: [{
    source: gamelift.Peer.anyIpv4(),
    port: gamelift.Port.tcpRange(100, 200),
  }]
});
// Allowing a specific CIDR for port 1111 on UDP Protocol
fleet.addIngressRule(gamelift.Peer.ipv4('1.2.3.4/32'), gamelift.Port.udp(1111));

Example not in your language?

Managing locations

A single Amazon GameLift fleet has a home Region by default (the Region you deploy it to), but it can deploy resources to any number of GameLift supported Regions. Select Regions based on where your players are located and your latency needs.

By default, home region is used as default location but we can add new locations if needed and define desired capacity

declare const build: gamelift.Build;

// Locations can be added directly through constructor
const fleet = new gamelift.BuildFleet(this, 'Game server fleet', {
  fleetName: 'test-fleet',
  content: build,
  instanceType: ec2.InstanceType.of(ec2.InstanceClass.C4, ec2.InstanceSize.LARGE),
  runtimeConfiguration: {
    serverProcesses: [{
      launchPath: '/local/game/GameLiftExampleServer.x86_64',
    }]
  },
  locations: [ {
    region: 'eu-west-1',
    capacity: {
      desiredCapacity: 5,
      minSize: 2,
      maxSize: 10
    }
  }, {
    region: 'us-east-1',
    capacity: {
      desiredCapacity: 5,
      minSize: 2,
      maxSize: 10
    }
  }]
});

// Or through dedicated methods
fleet.addLocation('ap-southeast-1', 5, 2, 10);

Example not in your language?

Specifying an IAM role for a Fleet

Some GameLift features require you to extend limited access to your AWS resources. This is done by creating an AWS IAM role. The GameLift Fleet class automatically created an IAM role with all the minimum necessary permissions for GameLift to access your resources. If you wish, you may specify your own IAM role.

declare const build: gamelift.Build;
const role = new iam.Role(this, 'Role', {
  assumedBy: new iam.CompositePrincipal(new iam.ServicePrincipal('gamelift.amazonaws.com'))
});
role.addManagedPolicy(iam.ManagedPolicy.fromAwsManagedPolicyName('CloudWatchAgentServerPolicy'));

const fleet = new gamelift.BuildFleet(this, 'Game server fleet', {
  fleetName: 'test-fleet',
  content: build,
  instanceType: ec2.InstanceType.of(ec2.InstanceClass.C5, ec2.InstanceSize.LARGE),
  runtimeConfiguration: {
    serverProcesses: [{
      launchPath: '/local/game/GameLiftExampleServer.x86_64',
    }]
  },
  role: role
});

// Actions can also be grantted through dedicated method
fleet.grant(role, 'gamelift:ListFleets');

Example not in your language?

Alias

A GameLift alias is used to abstract a fleet designation. Fleet designations tell Amazon GameLift where to search for available resources when creating new game sessions for players. By using aliases instead of specific fleet IDs, you can more easily and seamlessly switch player traffic from one fleet to another by changing the alias's target location.

declare const fleet: gamelift.BuildFleet;

// Add an alias to an existing fleet using a dedicated fleet method
const liveAlias = fleet.addAlias('live');

// You can also create a standalone alias
new gamelift.Alias(this, 'TerminalAlias', {
  aliasName: 'terminal-alias',
  terminalMessage: 'A terminal message',
});

Example not in your language?

See Add an alias to a GameLift fleet in the Amazon GameLift Developer Guide.

Monitoring your Fleet

GameLift is integrated with CloudWatch, so you can monitor the performance of your game servers via logs and metrics.

Fleet Metrics

GameLift Fleet sends metrics to CloudWatch so that you can collect and analyze the activity of your Fleet, including game and player sessions and server processes.

You can then use CloudWatch alarms to alert you, for example, when matches has been rejected (potential matches that were rejected by at least one player since the last report) exceed a certain threshold which could means that you may have an issue in your matchmaking rules.

CDK provides methods for accessing GameLift Fleet metrics with default configuration, such as metricActiveInstances, or metricIdleInstances (see IFleet for a full list). CDK also provides a generic metric method that can be used to produce metric configurations for any metric provided by GameLift Fleet, Game sessions or server processes; the configurations are pre-populated with the correct dimensions for the matchmaking configuration.

declare const fleet: gamelift.BuildFleet;
// Alarm that triggers when the per-second average of not used instances exceed 10%
const instancesUsedRatio = new cloudwatch.MathExpression({
  expression: '1 - (activeInstances / idleInstances)',
  usingMetrics: {
    activeInstances: fleet.metric('ActiveInstances', { statistic: cloudwatch.Statistic.SUM }),
    idleInstances: fleet.metricIdleInstances(),
  },
});
new cloudwatch.Alarm(this, 'Alarm', {
  metric: instancesUsedRatio,
  threshold: 0.1,
  evaluationPeriods: 3,
});

Example not in your language?

See: Monitoring Using CloudWatch Metrics in the Amazon GameLift Developer Guide.

Game session queue

The game session queue is the primary mechanism for processing new game session requests and locating available game servers to host them. Although it is possible to request a new game session be hosted on specific fleet or location.

The GameSessionQueue resource creates a placement queue that processes requests for new game sessions. A queue uses FleetIQ algorithms to determine the best placement locations and find an available game server, then prompts the game server to start a new game session. Queues can have destinations (GameLift fleets or aliases), which determine where the queue can place new game sessions. A queue can have destinations with varied fleet type (Spot and On-Demand), instance type, and AWS Region.

declare const fleet: gamelift.BuildFleet;
declare const alias: gamelift.Alias;

const queue = new gamelift.GameSessionQueue(this, 'GameSessionQueue', {
  gameSessionQueueName: 'my-queue-name',
  destinations: [fleet]
});
queue.addDestination(alias);

Example not in your language?

A more complex configuration can also be definied to override how FleetIQ algorithms prioritize game session placement in order to favour a destination based on Cost, Latency, Destination orderor Location.

declare const fleet: gamelift.BuildFleet;
declare const topic: sns.Topic;

new gamelift.GameSessionQueue(this, 'MyGameSessionQueue', {
      gameSessionQueueName: 'test-gameSessionQueue',
      customEventData: 'test-event-data',
      allowedLocations: ['eu-west-1', 'eu-west-2'],
      destinations: [fleet],
      notificationTarget: topic,
      playerLatencyPolicies: [{
        maximumIndividualPlayerLatency: Duration.millis(100),
        policyDuration: Duration.seconds(300),
      }],
      priorityConfiguration: {
        locationOrder: [
          'eu-west-1',
          'eu-west-2',
        ],
        priorityOrder: [
          gamelift.PriorityType.LATENCY,
          gamelift.PriorityType.COST,
          gamelift.PriorityType.DESTINATION,
          gamelift.PriorityType.LOCATION,
        ],
      },
      timeout: Duration.seconds(300),
    });

Example not in your language?

See Setting up GameLift queues for game session placement in the Amazon GameLift Developer Guide.

GameLift FleetIQ

The GameLift FleetIQ solution is a game hosting layer that supplements the full set of computing resource management tools that you get with Amazon EC2 and Auto Scaling. This solution lets you directly manage your Amazon EC2 and Auto Scaling resources and integrate as needed with other AWS services.

Defining a Game Server Group

When using GameLift FleetIQ, you prepare to launch Amazon EC2 instances as usual: make an Amazon Machine Image (AMI) with your game server software, create an Amazon EC2 launch template, and define configuration settings for an Auto Scaling group. However, instead of creating an Auto Scaling group directly, you create a GameLift FleetIQ game server group with your Amazon EC2 and Auto Scaling resources and configuration. All game server groups must have at least two instance types defined for it.

Once a game server group and Auto Scaling group are up and running with instances deployed, when updating a Game Server Group instance, only certain properties in the Auto Scaling group may be overwrite. For all other Auto Scaling group properties, such as MinSize, MaxSize, and LaunchTemplate, you can modify these directly on the Auto Scaling group using the AWS Console or dedicated Api.

declare const launchTemplate: ec2.ILaunchTemplate;
declare const vpc: ec2.IVpc;

new gamelift.GameServerGroup(this, 'Game server group', {
  gameServerGroupName: 'sample-gameservergroup-name',
  instanceDefinitions: [{
    instanceType: ec2.InstanceType.of(ec2.InstanceClass.C5, ec2.InstanceSize.LARGE),
  },
  {
    instanceType: ec2.InstanceType.of(ec2.InstanceClass.C4, ec2.InstanceSize.LARGE),
  }],
  launchTemplate: launchTemplate,
  vpc: vpc
});

Example not in your language?

See Manage game server groups in the Amazon GameLift FleetIQ Developer Guide.

Scaling Policy

The scaling policy uses the metric PercentUtilizedGameServers to maintain a buffer of idle game servers that can immediately accommodate new games and players.

declare const launchTemplate: ec2.ILaunchTemplate;
declare const vpc: ec2.IVpc;

new gamelift.GameServerGroup(this, 'Game server group', {
  gameServerGroupName: 'sample-gameservergroup-name',
  instanceDefinitions: [{
    instanceType: ec2.InstanceType.of(ec2.InstanceClass.C5, ec2.InstanceSize.LARGE),
  },
  {
    instanceType: ec2.InstanceType.of(ec2.InstanceClass.C4, ec2.InstanceSize.LARGE),
  }],
  launchTemplate: launchTemplate,
  vpc: vpc,
  autoScalingPolicy: {
    estimatedInstanceWarmup: Duration.minutes(5),
    targetTrackingConfiguration: 5
  }
});

Example not in your language?

See Manage game server groups in the Amazon GameLift FleetIQ Developer Guide.

Specifying an IAM role for GameLift

The GameLift FleetIQ class automatically creates an IAM role with all the minimum necessary permissions for GameLift to access your Amazon EC2 Auto Scaling groups. If you wish, you may specify your own IAM role. It must have the correct permissions, or FleetIQ creation or resource usage may fail.

declare const launchTemplate: ec2.ILaunchTemplate;
declare const vpc: ec2.IVpc;

const role = new iam.Role(this, 'Role', {
  assumedBy: new iam.CompositePrincipal(new iam.ServicePrincipal('gamelift.amazonaws.com'),
  new iam.ServicePrincipal('autoscaling.amazonaws.com'))
});
role.addManagedPolicy(iam.ManagedPolicy.fromAwsManagedPolicyName('GameLiftGameServerGroupPolicy'));

new gamelift.GameServerGroup(this, 'Game server group', {
  gameServerGroupName: 'sample-gameservergroup-name',
  instanceDefinitions: [{
    instanceType: ec2.InstanceType.of(ec2.InstanceClass.C5, ec2.InstanceSize.LARGE),
  },
  {
    instanceType: ec2.InstanceType.of(ec2.InstanceClass.C4, ec2.InstanceSize.LARGE),
  }],
  launchTemplate: launchTemplate,
  vpc: vpc,
  role: role
});

Example not in your language?

See Controlling Access in the Amazon GameLift FleetIQ Developer Guide.

Specifying VPC Subnets

GameLift FleetIQ use by default, all supported GameLift FleetIQ Availability Zones in your chosen region. You can override this parameter to specify VPCs subnets that you've set up.

This property cannot be updated after the game server group is created, and the corresponding Auto Scaling group will always use the property value that is set with this request, even if the Auto Scaling group is updated directly.

declare const launchTemplate: ec2.ILaunchTemplate;
declare const vpc: ec2.IVpc;

new gamelift.GameServerGroup(this, 'GameServerGroup', {
  gameServerGroupName: 'sample-gameservergroup-name',
  instanceDefinitions: [{
    instanceType: ec2.InstanceType.of(ec2.InstanceClass.C5, ec2.InstanceSize.LARGE),
  },
  {
    instanceType: ec2.InstanceType.of(ec2.InstanceClass.C4, ec2.InstanceSize.LARGE),
  }],
  launchTemplate: launchTemplate,
  vpc: vpc,
  vpcSubnets: { subnetType: ec2.SubnetType.PUBLIC }
});

Example not in your language?

FleetIQ Monitoring

GameLift FleetIQ sends metrics to CloudWatch so that you can collect and analyze the activity of your Game server fleet, including the number of utilized game servers, and the number of game server interruption due to limited Spot availability.

You can then use CloudWatch alarms to alert you, for example, when the portion of game servers that are currently supporting game executions exceed a certain threshold which could means that your autoscaling policy need to be adjust to add more instances to match with player demand.

CDK provides a generic metric method that can be used to produce metric configurations for any metric provided by GameLift FleetIQ; the configurations are pre-populated with the correct dimensions for the matchmaking configuration.

declare const gameServerGroup: gamelift.IGameServerGroup;
// Alarm that triggers when the percent of utilized game servers exceed 90%
new cloudwatch.Alarm(this, 'Alarm', {
  metric: gameServerGroup.metric('UtilizedGameServers'),
  threshold: 0.9,
  evaluationPeriods: 2,
});

Example not in your language?

See: Monitoring with CloudWatch in the Amazon GameLift FleetIQ Developer Guide.