AWSTemplateFormatVersion: '2010-09-09'
Transform: AWS::Serverless-2016-10-31
Description: Gracefully drain k8s nodes when instances are terminated (uksb-1pf6fjp67)

Parameters:

  AutoScalingGroup:
    Type: String

  EksCluster:
    Type: String

Globals:
    Function:
        Timeout: 300

Resources:

    LifecycleHook:
      Type: AWS::AutoScaling::LifecycleHook
      Properties:
        AutoScalingGroupName: !Ref AutoScalingGroup
        HeartbeatTimeout: 450
        LifecycleTransition: autoscaling:EC2_INSTANCE_TERMINATING

    DrainerRole:
      Type: AWS::IAM::Role
      Properties:
        AssumeRolePolicyDocument:
          Version: 2012-10-17
          Statement:
            - Effect: Allow
              Principal:
                Service:
                  - lambda.amazonaws.com
              Action:
                - sts:AssumeRole
        Path: /
        Policies:
          - PolicyName: DrainerPolicies
            PolicyDocument:
              Version: 2012-10-17
              Statement:
                - Effect: Allow
                  Action:
                    - autoscaling:CompleteLifecycleAction
                    - ec2:DescribeInstances
                    - eks:DescribeCluster
                    - sts:GetCallerIdentity
                  Resource: '*'
        ManagedPolicyArns:
          - arn:aws:iam::aws:policy/service-role/AWSLambdaBasicExecutionRole

    DrainerFunction:
        Type: AWS::Serverless::Function
        Properties:
          CodeUri: drainer/
          Handler: handler.lambda_handler
          Runtime: python3.7
          MemorySize: 256
          Environment:
            Variables:
              CLUSTER_NAME: !Ref EksCluster
          Role: !GetAtt DrainerRole.Arn
          Events:
            TerminationEvent:
              Type: CloudWatchEvent
              Properties:
                Pattern:
                  source:
                    - aws.autoscaling
                  detail-type:
                    - EC2 Instance-terminate Lifecycle Action
                  detail:
                    AutoScalingGroupName:
                      - !Ref AutoScalingGroup

    Permission:
      Type: AWS::Lambda::Permission
      Properties:
        Action: lambda:InvokeFunction
        FunctionName: !GetAtt DrainerFunction.Arn
        Principal: events.amazonaws.com

Outputs:

    DrainerRole:
      Description: Draining function role ARN
      Value: !GetAtt DrainerRole.Arn