Using Conditions and Parameters in CloudFormation - amazon-web-services

Question

I am trying to create a condition based on an optional parameter. The option is whether to run some additional installation from my userData script for an EC2 deployment.
The parameters and conditions look like this:
Parameters:
EnvType:
Description: Option to install New Relic Infrastructure.
Default: apm
Type: String
AllowedValues:
- apm
- +infra
Then my EC2 Resource with conditional startup scripts
Resources:
Ec2Instance:
Type: AWS::EC2::Instance
Properties:
InstanceType: t2.micro
ImageId: ami-9c9443e3 #Amazon Linux AMI in Tokyo
KeyName: tokyocloudformation
IamInstanceProfile: 'S3EC2'
SecurityGroupIds:
- !Ref myNewSecurityGroup
UserData:
Condition: apmOnly
Fn::Base64:
|
#!/bin/bash
installstuff
Condition: addInfrastructureAgent
Fn::Base64:
|
#!/bin/bash
installstuff
installsomeotherstuff
The error message I'm getting is:
Template validation error: Template format error: Unresolved dependencies [EnvTyp]. Cannot reference resources in the Conditions block of the template
I get what the error is saying I believe, but it doesn't seem to fit with the examples given by AWS.
https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/conditions-section-structure.html .
This AWS example clearly uses a !Ref in the Conditions block.
EnvType:
Description: Environment type.
Default: test
Type: String
AllowedValues:
- prod
- test
ConstraintDescription: must specify prod or test.
Conditions:
CreateProdResources: !Equals [ !Ref EnvType, prod ]
Can someone provide some feedback on how to implement this conditional or why this error message is being thrown for this implementation?

Answer 1

According to the docs, Conditions should be used at the top level of the resource you want to conditionally create.
Putting a Condition inside the Instance UserData section isn't supported.
To use Conditions in your situation, you'd want separate Resources conditionally created based on the Parameter.
Resources:
Ec2InstanceAPMOnly:
Type: AWS::EC2::Instance
Condition: apmOnly
Properties:
InstanceType: t2.micro
ImageId: ami-9c9443e3 #Amazon Linux AMI in Tokyo
KeyName: tokyocloudformation
IamInstanceProfile: 'S3EC2'
SecurityGroupIds:
- !Ref myNewSecurityGroup
UserData:
Fn::Base64:
!Sub |
#!/bin/bash
installstuff
Ec2InstanceWithInfrastructureAgent:
Type: AWS::EC2::Instance
Condition: addInfrastructureAgent
Properties:
InstanceType: t2.micro
ImageId: ami-9c9443e3 #Amazon Linux AMI in Tokyo
KeyName: tokyocloudformation
IamInstanceProfile: 'S3EC2'
SecurityGroupIds:
- !Ref myNewSecurityGroup
UserData:
Fn::Base64:
!Sub |
#!/bin/bash
installstuff
installsomeotherstuff

Answer 2

You can use Conditions in userData as well. i followed this post https://www.singlestoneconsulting.com/blog/cloudformation-mapping-and-conditionals-making-your-templates-more-universal/ and it worked perfactlly