Create autoscaling webserver group add to existing elb

Question

I have an Elastic Load Balancer already configured with ports and SSL certificates etc and Route 53 is set to route traffic for my site to it.

I'd like to know if there is an example cloudFormation template that creates an auto-scaling group of ec2 instances where each instance is added and removed to/from this existing load balancer.

I've looked around online for examples - the one below seems to be nearly what I need, but the problem with it (and all the others which appear to use variations of this) is that it presumes you want to create a NEW load balancer. I do not.

https://s3.amazonaws.com/cloudformation-templates-us-east-1/AutoScalingMultiAZWithNotifications.template

Is it possible, to do what I'm suggesting? Does someone have an example?

My CloudFormation script looks like below ( I removed the actual server package config part). This successfully creates a new instance, but it does not add to load balancer "load4". I can add the host to the load balancer manually, but this defeats the purpose obviously.

{
"AWSTemplateFormatVersion" : "2010-09-09",

"Description" : "Create an Auto-scaling group that will attach to existing load balancer and inhereit existing security groups.",

"Parameters" : {
"KeyName" : {
    "Description" : "mykeyname",
    "Type" : "String" 
},

"InstanceType" : {
    "Type" : "String", 
    "Default" : "m1.small", 
    "AllowedValues" : [ "m1.small", "m1.medium", "m1.large", "m1.xlarge", "m2.xlarge", "m2.2xlarge", "m2.4xlarge", "c1.xlarge", "cc1.4xlarge" ],
    "Description" : "EC2 instance type (e.g. m1.large, m1.xlarge, m2.xlarge)"
},
"SpotPrice": {
    "Description": "Spot price for application AutoScaling Group",
    "Type": "Number",
    "MinValue" : ".03"
},
"MinInstances" : {
  "Description" : "The minimum number of Workers",
  "Type" : "Number",
  "MinValue" : "0",
  "Default"  : "0",
  "ConstraintDescription" : "Enter a number >=0"
},

"MaxInstances" : {
  "Description" : "The maximum number of Workers",
  "Type" : "Number",
  "MinValue" : "1",
  "Default"  : "4",
  "ConstraintDescription" : "Enter a number >1"
},

"OperatorEmail": {
  "Description": "Email address to notify if there are any scaling operations",
  "Type": "String"
}
},

"Mappings" : {
"AWSInstanceType2Arch" : {
  "t1.micro"    : { "Arch" : "64" },
  "m1.small"    : { "Arch" : "64" },
  "m1.medium"   : { "Arch" : "64" },
  "m1.large"    : { "Arch" : "64" },
  "m1.xlarge"   : { "Arch" : "64" },
  "m2.xlarge"   : { "Arch" : "64" },
  "m2.2xlarge"  : { "Arch" : "64" },
  "m2.4xlarge"  : { "Arch" : "64" },
  "m3.xlarge"   : { "Arch" : "64" },
  "m3.2xlarge"  : { "Arch" : "64" },
  "c1.medium"   : { "Arch" : "64" },
  "c1.xlarge"   : { "Arch" : "64" },
  "cc1.4xlarge" : { "Arch" : "64HVM" },
  "cc2.8xlarge" : { "Arch" : "64HVM" },
  "cg1.4xlarge" : { "Arch" : "64HVM" }
},

"AWSRegionArch2AMI" : {
  "us-east-1"      : { "32" : "ami-31814f58", "64" : "ami-1b814f72", "64HVM" : "ami-0da96764" },
  "us-west-2"      : { "32" : "ami-38fe7308", "64" : "ami-30fe7300", "64HVM" : "NOT_YET_SUPPORTED" },
  "us-west-1"      : { "32" : "ami-11d68a54", "64" : "ami-1bd68a5e", "64HVM" : "NOT_YET_SUPPORTED" },
  "eu-west-1"      : { "32" : "ami-973b06e3", "64" : "ami-953b06e1", "64HVM" : "NOT_YET_SUPPORTED" },
  "ap-southeast-1" : { "32" : "ami-b4b0cae6", "64" : "ami-beb0caec", "64HVM" : "NOT_YET_SUPPORTED" },
  "ap-southeast-2" : { "32" : "ami-b3990e89", "64" : "ami-bd990e87", "64HVM" : "NOT_YET_SUPPORTED" },
  "ap-northeast-1" : { "32" : "ami-0644f007", "64" : "ami-0a44f00b", "64HVM" : "NOT_YET_SUPPORTED" },
  "sa-east-1"      : { "32" : "ami-3e3be423", "64" : "ami-3c3be421", "64HVM" : "NOT_YET_SUPPORTED" }
}
},

"Resources" : {
"NotificationTopic": {
  "Type": "AWS::SNS::Topic",
  "Properties": {
    "Subscription": [ {
        "Endpoint": { "Ref": "OperatorEmail" },
        "Protocol": "email" } ]
  }
},

"WebServerGroup" : {
  "Type" : "AWS::AutoScaling::AutoScalingGroup",
  "Properties" : {
    "AvailabilityZones" : { "Fn::GetAZs" : ""},
    "LaunchConfigurationName" : { "Ref" : "LaunchConfig" },
    "MinSize" : "0",
    "MaxSize" : "4",
    "LoadBalancerNames" : [ "load4" ],             
    "NotificationConfiguration" : {
      "TopicARN" : { "Ref" : "NotificationTopic" },
      "NotificationTypes" : [ "autoscaling:EC2_INSTANCE_LAUNCH","autoscaling:EC2_INSTANCE_LAUNCH_ERROR","autoscaling:EC2_INSTANCE_TERMINATE", "autoscaling:EC2_INSTANCE_TERMINATE_ERROR"]
    }
  }
},

"CfnUser" : {
    "Type" : "AWS::IAM::User",
    "Properties" : {
        "Path": "/",
        "Policies": [ {
            "PolicyName": "root",
            "PolicyDocument": { "Statement": [ {
                "Effect":"Allow",
                "Action":"cloudformation:DescribeStackResource",
                "Resource":"*"
            } ] }
        } ]
    }
},

"HostKeys" : {
    "Type" : "AWS::IAM::AccessKey",
    "Properties" : {
        "UserName" : { "Ref" : "CfnUser" }
    }
},

"LaunchConfig" : {
  "Type" : "AWS::AutoScaling::LaunchConfiguration",
  "Metadata" : {
    "Comment" : "Create a single webserver",
    "AWS::CloudFormation::Init" : {
      "config" : {
        "packages" : {
            "yum" : {

            }
        },
        "files" : {

        }
      }
    }
  },
  "Properties" : {
    "KeyName" : { "Ref" : "KeyName" },
    "SpotPrice" : { "Ref" : "SpotPrice" },
    "ImageId" : { "Fn::FindInMap" : [ "AWSRegionArch2AMI", { "Ref" : "AWS::Region" },
                                      { "Fn::FindInMap" : [ "AWSInstanceType2Arch", {     "Ref" : "InstanceType" },
                                      "Arch" ] } ] },
    "SecurityGroups" : [ "webserver" ],
    "InstanceType" : { "Ref" : "InstanceType" },
    "UserData"       : { "Fn::Base64" : { "Fn::Join" : ["", [
      "#!/bin/bash\n",
      "yum update -y aws-cfn-bootstrap\n",
      "# Install the Worker application\n",
      "/opt/aws/bin/cfn-init ",
      "         --stack ", { "Ref" : "AWS::StackId" },
      "         --resource LaunchConfig ",
      "         --configset ALL",
      "         --region ", { "Ref" : "AWS::Region" }, "\n"
    ]]}}        
  }
},

"WorkerGroup" : {
  "Type" : "AWS::AutoScaling::AutoScalingGroup",
  "Properties" : {
    "AvailabilityZones" : { "Fn::GetAZs" : ""},
    "LaunchConfigurationName" : { "Ref" : "LaunchConfig" },
    "MinSize" : { "Ref" : "MinInstances" },
    "MaxSize" : { "Ref" : "MaxInstances" }
  }
},


"WebServerScaleUpPolicy" : {
  "Type" : "AWS::AutoScaling::ScalingPolicy",
  "Properties" : {
    "AdjustmentType" : "ChangeInCapacity",
    "AutoScalingGroupName" : { "Ref" : "WorkerGroup" },
    "Cooldown" : "60",
    "ScalingAdjustment" : "1"
  }
},
"WebServerScaleDownPolicy" : {
  "Type" : "AWS::AutoScaling::ScalingPolicy",
  "Properties" : {
    "AdjustmentType" : "ChangeInCapacity",
    "AutoScalingGroupName" : { "Ref" : "WorkerGroup" },
    "Cooldown" : "60",
    "ScalingAdjustment" : "-1"
  }
},  ...




  "WorkerThreadHigh": {
   "Type": "AWS::CloudWatch::Alarm",
   "Properties": {
      "AlarmDescription": "Scale-up if Worker Thread Vs. Idle Percent > 80% for 10min",
      "MetricName": "PctActiveWorkers",
      "Namespace": "EC2",
      "Statistic": "Average",
      "Period": "300",
      "EvaluationPeriods": "2",
      "Threshold": "80",
      "AlarmActions": [ { "Ref": "WebServerScaleUpPolicy" } ],
      "Dimensions": [
        {
          "Name": "AutoScalingGroupName",
          "Value": { "Ref": "WebServerGroup" }
        }
      ],
      "ComparisonOperator": "GreaterThanThreshold"
    }
  },
  "WorkerThreadLow": {
   "Type": "AWS::CloudWatch::Alarm",
   "Properties": {
      "AlarmDescription": "Scale-down if CPU < 50% for 10 minutes",
      "MetricName": "PctActiveWorkers",
      "Namespace": "EC2",
      "Statistic": "Average",
      "Period": "300",
      "EvaluationPeriods": "2",
      "Threshold": "50",
      "AlarmActions": [ { "Ref": "WebServerScaleDownPolicy" } ],
      "Dimensions": [
        {
          "Name": "AutoScalingGroupName",
          "Value": { "Ref": "WebServerGroup" }
        }
      ],
      "ComparisonOperator": "LessThanThreshold"
    }
  }
}

}

Answer 1

You cannot decouple the two. I have verified with Amazon support for an unrelated use case. It sucks.

Here's our discussion. https://forums.aws.amazon.com/thread.jspa?messageID=362467&#362467 Amazon not replying at the end there is their way of saying, we don't support that.

UPDATE My answer below is no longer correct. Amazon has added this functionality. See other discussions.

Answer 2

Parameter LoadBalancerNames simply denotes A list of load balancers associated with this auto scaling group. The sample AWS CloudFormation template you reference (and indeed all other examples I'm aware of) has this configured to the result of the LoadBalancer resource as follows:

"LoadBalancerNames": [
    {
        "Ref": "ElasticLoadBalancer"
    }
],

The result of the Ref function is defined in section Return Values at the bottom of LoadBalancer:

When the logical ID of this resource is provided to the Ref intrinsic function, it returns the resource name. For example, mystack-myelb-1WQN7BJGDB5YQ.

This is simply the Load Balancer Name as shown in the AWS Management Console, accordingly you can use any Elastic Load Balancer created outside of CloudFormation by supplying its name directly, e.g.:

"LoadBalancerNames": [ "existing-load-balancer-1" ],

Answer 3

I can confirm that the following works, when added to the config of a resource of "Type": "AWS::AutoScaling::AutoScalingGroup":

"LoadBalancerNames" : [ "YourELBNameHere" ]

or, if you have the name as a parameter,

"LoadBalancerNames" : [ {"Ref" : "YourELBParameterNameHere"} ]

• the instances created by the ASG are added to/registered with the ELB, and removed/deregistered automatically, if you terminate the stack.