Cloudformation - Using parameters in EC2 server - amazon-web-services

Question

Below is my cloudformation template. Basically I want to use a parameter called "User" in a command in EC2 ubuntu server.
I have tried many solutions, but the mkdir command is not fails, rest of the template is working.
In the below example I have tried to set the "User" value as a tag as well as a property. Both failed. Suggest if you have seen any such examples.
{
"AWSTemplateFormatVersion": "2010-09-09",
"Parameters": {
"UserName": {
"Type": "String",
"Description": "Enter the username",
"AllowedPattern": "[a-zA-Z0-9_\\-]+",
"ConstraintDescription": "It should be a combination of characters from [A-Z],[a-z],[0-9],- and _."
},
"KeyName": {
"Description" : "Name of an existing EC2 KeyPair to enable SSH access to the instances",
"Type": "AWS::EC2::KeyPair::KeyName",
"ConstraintDescription" : "must be the name of an existing EC2 KeyPair."
}
},
"Resources": {
"EC2Ansiblemaster2743": {
"Type": "AWS::EC2::Instance",
"Metadata": {
"User" : { "Ref": "UserName" },
"AWS::CloudFormation::Init" : {
"configSets" : {
"CreateFile" : [
"create_file"
]
},
"create_file" : {
"files" : {
"/home/ubuntu/healthy.txt": {
"content": "Hello"
}
},
"commands" : {
"mkdir" : {
"command" : "sudo mkdir /home/$User"
}
}
}}
},
"Properties": {
"AvailabilityZone": "us-east-2a",
"ImageId": "ami-05c1fa8df71875112",
"InstanceType": "t2.micro",
"SourceDestCheck": false,
"KeyName" : { "Ref" : "KeyName" },
"Tags" : [
{
"Key" : "User",
"Value" : { "Ref": "UserName" }
}],
"UserData": {
"Fn::Base64": {
"Fn::Join": [
"",
[
"#!/bin/bash -xe\n",
"sudo apt-get update\n",
"sudo apt-get -y install python-pip\n",
"sudo pip install https://s3.amazonaws.com/cloudformation-examples/aws-cfn-bootstrap-latest.tar.gz\n",
"# Install the files and packages from the metadata\n",
"sudo /usr/local/bin/cfn-init ",
" --stack ",
{
"Ref": "AWS::StackName"
},
" --resource EC2Ansiblemaster2743 ",
" --configsets CreateFile ",
" --region ",
{
"Ref": "AWS::Region"
},
"\n",
"# Signal the status from cfn-init\n",
"sudo /usr/local/bin/cfn-signal -e $? ",
" --stack ",
{
"Ref": "AWS::StackName"
},
" --resource EC2Ansiblemaster2743 ",
" --region ",
{
"Ref": "AWS::Region"
},
"\n"
]
]
}
},
"SecurityGroupIds": [
{
"Ref": "EC2SG2AnsM0012743"
}
]
}
},
"EC2SG2AnsM0012743": {
"Type": "AWS::EC2::SecurityGroup",
"Properties": {
"GroupName": "SGAnsibleMas2743",
"GroupDescription": "First",
"SecurityGroupIngress": [
{
"CidrIp": "0.0.0.0/0",
"FromPort": "0",
"ToPort": "65535",
"IpProtocol": "tcp",
"Description": "From Anywhere"
},
{
"CidrIp": "0.0.0.0/0",
"FromPort": "22",
"ToPort": "22",
"IpProtocol": "tcp",
"Description": "SSH from anywhere , from and to port will be same - 22"
}
]
},
}
}
}

Answer 1

I used the Fn:Sub to get the parameter to Userdata.
{
"Fn::Sub":
[
"UserName=${variable}\n",
{
"variable": {
"Ref": "UserName"
}
}]
Later I curl 169.254.169.254/latest/user-data to extract the Username string.
Please let me know if any easier solution is there for this issue.

Answer 2

Use the join intrinsic function to properly form the command string by referencing the username in the template.
"command" : "Fn::Join": [ "", "mkdir /home/", { "Ref": "UserName" }]
The issue is that your mkdir command does not resolve as you have it. There is no linkage between the username parameter and the command in the init section. By using the Join function I am forming the command with the correct parameter value.