Join function is used heavily in AWS CloudFormation. Take a look at
Amazon document
This function is convenient when set configuration in AWS Cloudformation.
"/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 WebServer ",
" --configsets wordpress_install ",
" --region ",
{
"Ref": "AWS::Region"
},
"\n"
]
]
},
"mode": "000400",
"owner": "root",
"group": "root"
}
Conditions in AWS CloudFormation
- Conditions in AWS CloudFormation allow for creating reusable templates with flexibility.
- They can be used in two ways: specifying the condition under the resource or using the conditional intrinsic function in resource properties.
- Conditions are strict Boolean variables evaluated by parameters and conditional functions.
- They can be used to adjust resource attributes based on different scenarios, such as creating resources with different attributes depending on the environment (e.g., test or production).
- In the example provided, a condition named “ProdEnv” is used with the conditional function Fn::If to determine whether the environment is production (m5.large instance) or test (t3.micro instance).