In `aws cloudformation deploy --parameter-overrides`, how to pass multiple values to `List<AWS::EC2::Subnet::ID>` parameter? - aws-cloudformation

Question

I am using this CloudFormation template
The List parameter I'm trying to pass values to is:
"Subnets" : {
"Type" : "List<AWS::EC2::Subnet::Id>",
"Description" : "The list of SubnetIds in your Virtual Private Cloud (VPC)",
"ConstraintDescription" : "must be a list of at least two existing subnets associated with at least two different availability zones. They should be residing in the selected Virtual Private Cloud."
},
I've written an utility script that looks like this:
#!/bin/bash
SUBNET1=subnet-abcdef
SUBNET2=subnet-ghijlm
echo -e "\n==Deploying stack.cf.yaml===\n"
aws cloudformation deploy \
--region $REGION \
--profile $CLI_PROFILE \
--stack-name $STACK_NAME \
--template-file stack.cf.json \
--no-fail-on-empty-changeset \
--capabilities CAPABILITY_NAMED_IAM \
--parameter-overrides \
VpcId=$VPC_ID \
Subnets="$SUBNET1 $SUBNET2" \ #<---------------this fails
InstanceType=$EC2_INSTANCE_TYPE \
OperatorEMail=$OPERATOR_EMAIL \
KeyName=$KEY_NAME \
If I deploy this, after a while my stack fails to deploy saying that a Subnet with the value "subnet-abcdef subnet-ghijlmn" does not exist.

Answer 1

The correct way to pass parameters to list is to comma separate them
So:
#!/bin/bash
SUBNET1=subnet-abcdef
SUBNET2=subnet-ghijlm
aws cloudformation deploy --parameter-overrides Subnets="$SUBNET1,SUBNET2"
will work

Answer 2

Tried every possible solution found online, none worked.
According to the documentation below, you should escape the comma without double-slashes. Tried that, didn't work either.
https://docs.aws.amazon.com/cli/latest/reference/cloudformation/create-stack.html
What worked FOR ME (apparently this is very environment-dependent) was the command below, escaping the coma with just one slash.
aws cloudformation create-stack --stack-name teste-memdb --template-body file://memorydb.yml --parameters ParameterKey=VpcId,ParameterValue=vpc-xxxx ParameterKey=SubnetIDs,ParameterValue=subnet-xxxxx\,subnet-yyyy --profile whatever

Answer 3

From the Documentation here
List/Array can be passed just like python Lists.
'["value1", "value2", "value3"]'
Also to note Cloudformation internally used python.