在opsworks中的自定义json中设置环境变量

I am working on a AWS cloudformation template that creates an opsworks stack. In my stack, I will have one instance (Ubuntu 14.04) , all the applications and packages that will be installed in the instance are configured in the chef cookbook provided from an S3 bucket. I need to set an environment variable in my instance and its value is to be set by a parameter of the cloudformation template, this is the template:I am working on a AWS cloudformation template t