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

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): }