Using Exported values - aws-cloudformation

Question

I am able to export the keys using this cloudformation template...
https://github.com/shantanuo/cloudformation/blob/master/restricted.template.txt
But how do I import the saved keys directly into "UserData" section of another template? I tried this, but does not work...
aws-ec2-assign-elastic-ip --access-key !Ref {"Fn::ImportValue" : "accessKey" } --secret-key --valid-ips 35.174.198.170
The rest of the template (without access and secret key reference) is working as expected.
https://github.com/shantanuo/cloudformation/blob/master/security.template2.txt

Answer 1

So, if this is your script that does the export (sorry, this one is in yaml)
AWSTemplateFormatVersion: '2010-09-09'
Metadata:
License: Apache-2.0
Description: 'AWS CloudFormation Sample Template'
Parameters:
NewUsername:
NoEcho: 'false'
Type: String
Description: New account username
MinLength: '1'
MaxLength: '41'
ConstraintDescription: the username must be between 1 and 41 characters
Password:
NoEcho: 'true'
Type: String
Description: New account password
MinLength: '1'
MaxLength: '41'
ConstraintDescription: the password must be between 1 and 41 characters
Resources:
CFNUser:
Type: AWS::IAM::User
Properties:
LoginProfile:
Password: !Ref 'Password'
UserName : !Ref 'NewUsername'
CFNAdminGroup:
Type: AWS::IAM::Group
Admins:
Type: AWS::IAM::UserToGroupAddition
Properties:
GroupName: !Ref 'CFNAdminGroup'
Users: [!Ref 'CFNUser']
CFNAdminPolicies:
Type: AWS::IAM::Policy
Properties:
PolicyName: CFNAdmins
PolicyDocument:
Statement:
- Effect: Allow
Action: '*'
Resource: '*'
Condition:
StringEquals:
aws:RequestedRegion:
- ap-south-1
- us-east-1
Groups: [!Ref 'CFNAdminGroup']
CFNKeys:
Type: AWS::IAM::AccessKey
Properties:
UserName: !Ref 'CFNUser'
Outputs:
AccessKey:
Value: !Ref 'CFNKeys'
Description: AWSAccessKeyId of new user
Export:
Name: 'accessKey'
SecretKey:
Value: !GetAtt [CFNKeys, SecretAccessKey]
Description: AWSSecretAccessKey of new user
Export:
Name: 'secretKey'
Then here is an example of how you would import those values in userdata in the import cloudformation script:
{
"AWSTemplateFormatVersion": "2010-09-09",
"Description": "Test instance stack",
"Parameters": {
"KeyName": {
"Description": "The EC2 Key Pair to allow SSH access to the instance",
"Type": "AWS::EC2::KeyPair::KeyName"
},
"BaseImage": {
"Description": "The AMI to use for machines.",
"Type": "String"
},
"VPCID": {
"Description": "ID of the VPC",
"Type": "String"
},
"SubnetID": {
"Description": "ID of the subnet",
"Type": "String"
}
},
"Resources": {
"InstanceSecGrp": {
"Type": "AWS::EC2::SecurityGroup",
"Properties": {
"GroupDescription": "Instance Security Group",
"SecurityGroupIngress": [{
"IpProtocol": "-1",
"CidrIp": "0.0.0.0/0"
}],
"SecurityGroupEgress": [{
"IpProtocol": "-1",
"CidrIp": "0.0.0.0/0"
}],
"VpcId": {
"Ref": "VPCID"
}
}
},
"SingleInstance": {
"Type": "AWS::EC2::Instance",
"Properties": {
"KeyName": {
"Ref": "KeyName"
},
"ImageId": {
"Ref": "BaseImage"
},
"InstanceType": "t2.micro",
"Monitoring": "false",
"BlockDeviceMappings": [{
"DeviceName": "/dev/xvda",
"Ebs": {
"VolumeSize": "20",
"VolumeType": "gp2"
}
}],
"NetworkInterfaces": [{
"GroupSet": [{
"Ref": "InstanceSecGrp"
}],
"AssociatePublicIpAddress": "true",
"DeviceIndex": "0",
"DeleteOnTermination": "true",
"SubnetId": {
"Ref": "SubnetID"
}
}],
"UserData": {
"Fn::Base64": {
"Fn::Join": ["", [
"#!/bin/bash -xe\n",
"yum install httpd -y\n",
"sudo sh -c \"echo ",
{ "Fn::ImportValue" : "secretKey" },
" >> /home/ec2-user/mysecret.txt\" \n",
"sudo sh -c \"echo ",
{ "Fn::ImportValue" : "accessKey" },
" >> /home/ec2-user/myaccesskey.txt\" \n"
]]
}
}
}
}
}
}
In this example I am just echoing the value of the import into a file. If you ssh onto the SingleInstance and check the logs at /var/lib/cloud/instance/scripts/part-001 then you will see what the user data script looks like on the server itself. In my case the contents of that file is (values aren't real for the keys):
#!/bin/bash -xe
yum install httpd -y
sudo sh -c "echo hAc7/TJA123143235ASFFgKWkKSjIC4 >> /home/ec2-user/mysecret.txt"
sudo sh -c "echo AKIAQ123456789123D >> /home/ec2-user/myaccesskey.txt"
Using this as a starting point you can do whatever you need to with the import value.
I've tested all of this with the exact scripts above and it all works.

Answer 2

What is suggested in the comments seems to be correct. I can directly refer to the name (for e.g. 'accessKey' in this case) using ImportValue!
AWSTemplateFormatVersion: '2010-09-09'
Metadata:
License: Apache-2.0
Description: 'AWS CloudFormation Sample Template'
Resources:
CFNUser:
Type: AWS::IAM::User
Outputs:
AccessKey:
Value:
Fn::ImportValue: accessKey
Description: AWSAccessKeyId of new user
For e.g. the above template will return the value of accessKey if it is already exported by some other template.