Use env variables inside cloudformation templates - amazon-web-services

Question

i have an amplify app with multiple branches.
I have added an custom cloudformation template with amplify add custom
It looks like:
{
"AWSTemplateFormatVersion": "2010-09-09",
"Parameters": { "env": { "Type": "String" } },
"Resources": {
"db": {
"Type": "AWS::Timestream::Database",
"Properties": { "DatabaseName": "dev_db" }
},
"timestreamtable": {
"DependsOn": "db",
"Type": "AWS::Timestream::Table",
"Properties": {
"DatabaseName": "dev_db",
"TableName": "avg_16_4h",
"MagneticStoreWriteProperties": { "EnableMagneticStoreWrites": true },
"RetentionProperties": {
"MemoryStoreRetentionPeriodInHours": "8640",
"MagneticStoreRetentionPeriodInDays": "1825"
}
}
}
},
"Outputs": {},
"Description": "{\"createdOn\":\"Windows\",\"createdBy\":\"Amplify\",\"createdWith\":\"8.3.1\",\"stackType\":\"custom-customCloudformation\",\"metadata\":{}}"
}
You can see there is a field called DatabaseName. In my amplify app i have written an env variable named TIMESTREAM_DB and i want to use it inside of this cloudformation file.
Is this possible or do i need to write it all by hand in it?

Answer 1

Templates cannot access arbitrary env vars. Instead, CloudFormation injects deploy-time values into a template with Parameters.
Amplify helpfully adds the env variable as a parameter. A la the Amplify docs, use the env value as the AWS::Timestream::Database name suffix:
"DatabaseName": "Fn::Join": [ "", [ "my-timestream-db-name-", { "Ref": "env" } ] ]
The AWS::Timestream::Table resource also requires a DatabaseName parameter. You could repeat the above, but it's more DRY to get the name via the Database's Ref:
"DatabaseName": { "Ref" : "db" }