template.json

{
	"variables": {
			"aws_access_key": "test",
			"aws_secret_key": "test",
			"region":         "ap-south-1",
			"base_ami": "ami-0fd7e4b8e94538bef",
			"mongo_version": "4.2",
			"version": "1.0"
	},
	"builders": [
			{
					"access_key": "{{user `aws_access_key`}}",
					"ami_name": "ubuntu-18.04_mongodb-{{user `mongo_version`}}_{{user `version`}}",
					"instance_type": "t3.micro",
					"region": "{{user `region`}}",
					"secret_key": "{{user `aws_secret_key`}}",
					"source_ami":"{{user `base_ami`}}", 
					"ssh_username": "ubuntu",
					"tags": {
						"OS_Version": "Ubuntu"      
					},
					"type": "amazon-ebs"
			}
	],
	"provisioners": [
		{
			"type": "shell",
			"script": "./scripts/shutdown-apt-services.sh"
	},
		{
					"type": "shell",
					"environment_vars": [
						"MONGO_VERSION={{user `mongo_version`}}"
					],
					"script": "./scripts/provisioning.sh",
					"pause_before": "10s"
			}
	]
}