How to specify JSON-formatted string in Cloudformation? - json

Question

I have the following resource on my CloudFormation template to create a rule to run a Lambda function, from the AWS documentation:
"ScheduledRule": {
"Type": "AWS::Events::Rule",
"Properties": {
"Description": "ScheduledRule",
"ScheduleExpression": "rate(5 minutes)",
"State": "ENABLED",
"Targets": [{
"Arn": { "Fn::GetAtt": ["myLambda", "Arn"] },
"Id": "TargetFunctionV1"
}]
}
}
I would like to specify the Input:
{
"Arn" : String,
"Id" : String,
"Input" : String,
"InputPath" : String
}
and Input is a JSON-formatted text string that is passed to the target. This value overrides the matched event.
I would like my JSON formatted text to be:
{
"mykey1": "Some Value"
}
I do not know how to specify it in the Input, when I put:
"ScheduledRule": {
"Type": "AWS::Events::Rule",
"Properties": {
"Description": "ScheduledRule",
"ScheduleExpression": "rate(5 minutes)",
"State": "ENABLED",
"Targets": [{
"Arn": { "Fn::GetAtt": ["myLambda", "Arn"] },
"Id": "TargetFunctionV1",
"Input": { "mykey1": "Some Value" }
}]
}
}
I will get error:
Value of property Input must be of type String
How should I specify it correctly?

Answer 1

I would use YAML as it is easier and more readable:
Input:
!Sub |
{
mykey1: "${myKey}"
}

Answer 2

Found out the answer myself:
"Input": "{ \"test\" : \"value11\", \"test2\" : \"value22\"}"
Hope it helps someone else.
Update:
You basically use the result of JSON.Stringify() to get the string into "Input" field. Use online JSON.Stringify() like https://onlinetexttools.com/json-stringify-text

Answer 3

I wanted to expand on #Pau's answer. Basically if you use the | to say that the whole block below is to be treated as a raw string.
If you need to replace any variable in the JSON then you can use Sub, but if you don't have any variables, then you don't need Sub. An example would be:
Input:|
{
"jsonVar":"jsonVal",
"jsonVar2" : "jsonVal2"
}
You can later do JSON.parse(<input-variable>) to get the JSON object.
NOTE: Don't put commas at the end of the variables in JSON, if there is no next variable. Example :
Input:|
{
"jsonVar":"jsonVal",
"jsonVar2" : "jsonVal2",
}
This will cause JSON parsing errors.

Answer 4

If you are writing your CloudFormation scripts in yaml and finding it difficult to use a JSON string (such as a policy doc) the easiest way is to convert your JSON into yaml using an online converter
ApiGatewayRestApi:
Type: AWS::ApiGateway::RestApi
Properties:
Description: API Gateway for some API
EndpointConfiguration:
Types:
- PRIVATE
Name: MyAPIGateway
Policy: <Policy Doc >
Lets say the policy doc is as follows.
{
"Version": "2012-10-17",
"Statement": [
{
"Effect": "Allow",
"Principal": "*",
"Action": "execute-api:Invoke",
"Resource": "arn:aws:execute-api:ap-southeast-2:something/*",
"Condition": {
"ForAnyValue:StringEquals": {
"aws:sourceVpce": "vpce-abcd"
}
}
}
]
}
Using the converter you can convert the JSON into an identical yaml and use as follows.
ApiGatewayRestApi:
Type: AWS::ApiGateway::RestApi
Properties:
Description: API Gateway for some API
EndpointConfiguration:
Types:
- PRIVATE
Name: MyAPIGateway
Policy:
Version: '2012-10-17'
Statement:
- Effect: Allow
Principal: "*"
Action: execute-api:Invoke
Resource: arn:aws:execute-api:ap-southeast-2:something/*
Condition:
ForAnyValue:StringEquals:
aws:sourceVpce: vpce-abcd

Answer 5

Here's my similar YAML code for the "input" line. It took me all day to figure out the syntax so I'm hoping this might help someone in the future.
Input: "{\"action\":[\"configure\"],\"mode\":[\"ec2\"],\"optionalConfigurationSource\":[\"ssm\"],\"optionalConfigurationLocation\":[\"AmazonCloudWatch-Baseline-Windows\"],\"optionalRestart\":[\"yes\"]}"