serverless.yml

service: restartFargateServices
custom:
  snsTopic: "${self:service}-${self:provider.stage}-fargate-memory-alarms"
  snsTopicArn: { "Fn::Join" : ["", ["arn:aws:sns:${self:provider.region}:", { "Ref" : "AWS::AccountId" }, ":${self:custom.snsTopic}" ] ]  }
  myEnvironment:
    CLUSTER_NAME:
      production: "prod-railsapp"
      staging: "staging-railsapp"

provider:
  name: aws
  runtime: ruby2.5

  stage: ${opt:stage, 'staging'}
  region: eu-west-1

  iamRoleStatements:
    - Effect: Allow
      Action:
        - ecs:UpdateService
      Resource: '*'

functions:
  restartFargateServices:
    handler: handler.restart_service

    events:
      - sns: ${self:custom.snsTopic}

resources:
 Resources:
   ApiMemoryUsageAlarm:
     Type: AWS::CloudWatch::Alarm
     Properties:
       ActionsEnabled: true
       AlarmActions:
         - ${self:custom.snsTopicArn}
       AlarmName: ${self:service}:${self:provider.stage}:ApiMemoryUsageAlarm
       ComparisonOperator: GreaterThanOrEqualToThreshold
       Dimensions:
         - Name: ClusterName
           Value: ${self:custom.myEnvironment.CLUSTER_NAME.${self:provider.stage}}
         - Name: ServiceName
           Value: api
       EvaluationPeriods: 2
       MetricName: MemoryUtilization
       Namespace: AWS/ECS
       Period: 120
       Statistic: Maximum
       Threshold: 85.0
   AdminMemoryUsageAlarm:
     Type: AWS::CloudWatch::Alarm
     Properties:
       ActionsEnabled: true
       AlarmActions:
         - ${self:custom.snsTopicArn}
       AlarmName: ${self:service}:${self:provider.stage}:AdminMemoryUsageAlarm
       ComparisonOperator: GreaterThanOrEqualToThreshold
       Dimensions:
         - Name: ClusterName
           Value: ${self:custom.myEnvironment.CLUSTER_NAME.${self:provider.stage}}
         - Name: ServiceName
           Value: admin
       EvaluationPeriods: 2
       MetricName: MemoryUtilization
       Namespace: AWS/ECS
       Period: 120
       Statistic: Maximum
       Threshold: 85.0