How to prepare rendered JSON for aws-cli in Terraform? - amazon-web-services

Question

In another thread I have asked how to keep ECS task definitions active in AWS. As a result I am planning to update a task definition like this:
resource "null_resource" "update_task_definition" {
triggers {
keys = "${uuid()}"
}
# Workaround to prevent older task definitions being deactivated
provisioner "local-exec" {
command = <<EOF
aws ecs register-task-definition \
--family my-task-definition \
--container-definitions ${data.template_file.task_definition.rendered} \
--network-mode bridge \
EOF
}
}
data.template_file.task_definition is a template data source which provides templated JSON from a file. However, this does not work, since the JSON contains new lines and whitespaces.
I figured out already that I can use the replace interpolation function to get rid of new lines and whitespaces, however I still require to escape double quotes so that the AWS API accepts the request.
How can I safely prepare the string resulting from data.template_file.task_definition.rendered? I am looking for something like this:
Raw string:
{
"key": "value",
"another_key": "another_value"
}
Prepared string:
{\"key\":\"value\",\"another_key\":\"another_value\"}

Answer 1

You should be able to wrap the rendered JSON with the jsonencode function.
With the following Terraform code:
data "template_file" "example" {
template = file("example.tpl")
vars = {
foo = "foo"
bar = "bar"
}
}
resource "null_resource" "update_task_definition" {
triggers = {
keys = uuid()
}
provisioner "local-exec" {
command = <<EOF
echo ${jsonencode(data.template_file.example.rendered)}
EOF
}
}
And the following template file:
{
"key": "${foo}",
"another_key": "${bar}"
}
Running a Terraform apply gives the following output:
null_resource.update_task_definition: Creating...
triggers.%: "" => "1"
triggers.keys: "" => "18677676-4e59-8476-fdde-dc19cd7d2f34"
null_resource.update_task_definition: Provisioning with 'local-exec'...
null_resource.update_task_definition (local-exec): Executing: ["/bin/sh" "-c" "echo \"{\\n \\\"key\\\": \\\"foo\\\",\\n \\\"another_key\\\": \\\"bar\\\"\\n}\\n\"\n"]
null_resource.update_task_definition (local-exec): {
null_resource.update_task_definition (local-exec): "key": "foo",
null_resource.update_task_definition (local-exec): "another_key": "bar"
null_resource.update_task_definition (local-exec): }