cfn-signal in aws cloudformation with launchConfiguration and AutoScalingGroup - amazon-web-services

Question

I have the following configuration in my AWS Cloudformation template.
The template creates one EC2 instance based on instance1. I am using the reference to same instance in my LaunchConfiguration to create the instances of same type.
The problem I am facing is by including the CreationPolicy element in my AutoScalingGroup template. I get the following error when ASG launches an instance and waits for the cfn-signal.
+ /opt/aws/bin/cfn-signal -e 0 --stack ss07 --resource Instance1 --region us-west-2
ValidationError: Resource Instance1 is in CREATE_COMPLETE state and cannot be signaled
It seems like somehow the reference is made to an already existing instance1 and not to the instance being created by LaunchConfig. I saw examples which had the LaunchConfig embedded within, but I want to keep the instance details at one place instead of two places.
"instance1": {
"Type": "AWS::EC2::Instance",
"Metadata": {
"AWS::CloudFormation::Init": {
"configSets": {
"install": ["yum_packages","install_cfn"]
},
"yum_packages": {
"packages" : {
"yum" : {
"awslogs" : [],
"ruby" : [],
"wget" : [],
"httpd" : []
}
}
},
"install_cfn": {
"files": {
"/etc/cfn/cfn-hup.conf": {
"content": {
"Fn::Join": [
"",
[
"[main]\n",
"stack=",
{
"Ref": "AWS::StackId"
},
"\n",
"region=",
{
"Ref": "AWS::Region"
},
"\n"
]
]
},
"mode": "000400",
"owner": "root",
"group": "root"
},
"/etc/cfn/hooks.d/cfn-auto-reloader.conf": {
"content": {
"Fn::Join": [
"",
[
"[cfn-auto-reloader-hook]\n",
"triggers=post.update\n",
"path=Resources.WebServer.Metadata.AWS::CloudFormation::Init\n",
"action=/opt/aws/bin/cfn-init -v ",
" --stack ",
{
"Ref": "AWS::StackName"
},
" --resource splitsweetInstance ",
" --configsets install ",
" --region ",
{
"Ref": "AWS::Region"
},
"\n"
]
]
},
"mode": "000400",
"owner": "root",
"group": "root"
}
},
"services": {
"sysvinit": {
"cfn-hup": { "enabled": "true", "ensureRunning": "true", "files": [
"/etc/cfn/cfn-hup.conf",
"/etc/cfn/hooks.d/cfn-auto-reloader.conf"
]
}
}
}
}
}
},
"CreationPolicy": {
"ResourceSignal": {
"Timeout": "PT10M"
}
},
"Properties": {
"ImageId": {
"Fn::FindInMap": [
"AWSRegionArch2AMI", {
"Ref": "AWS::Region"
}, {
"Fn::FindInMap": [
"AWSInstanceType2Arch", {
"Ref": "instanceType1"
},
"Arch"
]
}
]
},
"InstanceType": {"Ref": "instanceType1"},
"KeyName": {"Ref": "KeyName"},
"Monitoring": "false",
"UserData" : { "Fn::Base64" : { "Fn::Join" : ["", [
"#!/bin/bash -xe\n",
"yum install -y aws-cfn-bootstrap\n",
"# Install the files and packages from the metadata\n",
"/opt/aws/bin/cfn-init -v ",
" --stack ", { "Ref" : "AWS::StackName" },
" --resource splitsweetInstance ",
" --configsets install ",
" --region ", { "Ref" : "AWS::Region" }, "\n",
"wget ", { "Fn::FindInMap": [ "Region2CodeDeployAgent", { "Ref": "AWS::Region"}, "url"] }, "\n",
"chmod +x ./install\n",
"./install auto\n",
"# Signal the status from cfn-init\n",
"/opt/aws/bin/cfn-signal -e $? ",
" --stack ", { "Ref" : "AWS::StackName" },
" --resource splitsweetInstance ",
" --region ", { "Ref" : "AWS::Region" }, "\n"
]]}},
"Tags": [
{
"Key": "Name",
"Value": "inst1"
}
],
"SecurityGroupIds": [
{ "Fn::GetAtt" : [ "instance1Sg", "GroupId" ] }
]
}
}
My Launch Config is as follows -
"LaunchConfig1": {
"Type" : "AWS::AutoScaling::LaunchConfiguration",
"Properties" : {
"ImageId": {
"Fn::FindInMap": [
"AWSRegionArch2AMI", {
"Ref": "AWS::Region"
}, {
"Fn::FindInMap": [
"AWSInstanceType2Arch", {
"Ref": "instanceType1"
},
"Arch"
]
}
]
},
"InstanceId" : { "Ref":"instance1"},
"InstanceMonitoring" : "false",
"InstanceType" : { "Ref": "instanceType1"},
"KeyName" : { "Ref" : "KeyName" },
"SecurityGroups" : [ { "Fn::GetAtt" : [ "instance1Sg", "GroupId" ] } ]
}
}
This is my AutoScalingGroup template -
"AutoScalingGroup1": {
"Type" : "AWS::AutoScaling::AutoScalingGroup",
"Properties" : {
"AvailabilityZones" : { "Fn::GetAZs": { "Ref": "AWS::Region" } },
"Cooldown" : "60",
....
"LaunchConfigurationName" : {"Ref":"LaunchConfig1"},
"MaxSize" : "3",
"MinSize" : "1",
"TargetGroupARNs" : [ {"Ref":"TargetGroup1"} ],
"VPCZoneIdentifier" : [ { "Ref": "subnetCache1" }, { "Ref": "subnetCache2" }, { "Ref": "subnetCache3" } ]
},
"CreationPolicy" : {
"ResourceSignal" : {
"Timeout" : "PT6M",
"Count" : "1"
}
}
}

Answer 1

The problem is that by specifying the InstanceId property in your LaunchConfiguration resource, it is reusing the same UserData that was used to launch the initial EC2 instance, including the hard-coded reference to the Logical Resource signaled by the cfn-signal command. According to the documentation,
When you use an instance to create a launch configuration, all properties are derived from the instance with the exception of BlockDeviceMapping and AssociatePublicIpAddress. You can override any properties from the instance by specifying them in the launch configuration.
To have cfn-signal signal the correct Resource, you will need to override the UserData in your LaunchConfiguration resource to contain a User-Data script that references the Launch Configuration rather than the original EC2 instance. Unfortunately, this will require either duplicating the User-Data script, or rewriting the script to dynamically figure out the Logical Resource associated with the instance the script is currently running on, so the same exact User-Data can be used in both the original EC2 instance and the auto scaling group.

Answer 2

I agree with wjordan that part of the problem you are having is with the InstanceId property in LaunchConfiguration. Also looking at your code sample I could not figure out where splitsweetInstance was referenced.
However my CloudFormation AutoScalingGroup was not set up this way and I still got the same error CREATE_COMPLETE state and cannot be signaled.
The solution for me was setting the DesiredCapacity on the AutoScalingGroup (hopefully this helps others as well) was found here:
http://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-properties-as-group.html#cfn-as-group-desiredcapacity
As per the docs:
CloudFormation will not mark the Auto Scaling group as successful (by setting its status to CREATE_COMPLETE) until the desired capacity is reached.
This is what that portion of my CloudFormation template looks like:
"WebServerGroup" : {
"Type" : "AWS::AutoScaling::AutoScalingGroup",
"Properties" : {
"VPCZoneIdentifier" : { "Ref" : "Subnets" },
"LaunchConfigurationName" : { "Ref" : "LaunchConfig" },
"MinSize" : "2",
"MaxSize" : "4",
"DesiredCapacity" : "2",
"TargetGroupARNs" : [ { "Ref" : "ALBTargetGroup" } ]
}
Below is the "signal" portion of UserData section:
"# Signal the status from cfn-init\n",
"/opt/aws/bin/cfn-signal -e $? ",
" --stack ", { "Ref" : "AWS::StackName" },
" --resource WebServerGroup ",
" --region ", { "Ref" : "AWS::Region" }, "\n",

Answer 3

To solve this problem I ensured that I added both CreationPolicy & UpdatePolicy in Autoscaling group before using cfn-signal in UserData section of the LaunchTemplate
CreationPolicy:
AutoScalingCreationPolicy:
MinSuccessfulInstancesPercent: somepercent
ResourceSignal:
Count: somenumber
Timeout: someminutes
UpdatePolicy:
AutoScalingScheduledAction:
IgnoreUnmodifiedGroupSizeProperties: 'true'
AutoScalingRollingUpdate:
MinInstancesInService: 'somenumber'
MaxBatchSize: 'somenumber'
PauseTime: someminutes
WaitOnResourceSignals: 'true'