Formatting a Packer Template in JSON

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Formatting a Packer Template in JSON

Packer allows us to create templates for generating cross-platform machine images — templates that can be written in JSON. In this lab, we'll test our JSON skills by fixing and otherwise neatening up an inaccurately written JSON Packer template. Just want to test your JSON reviewing skills? No Packer knowledge is needed to take this lab.

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Lab Info

Level

Beginner

Last updated

Apr 06, 2025

Duration

30m

Challenge

Fix Whitespace

Open the provided template:
```
cd packer
```
```
vim ami-test.json
```

To make viewing the template easier, let's neaten it up by adjusting the tabs/whitespace:

{
    "variables": {
        "aws_access_key": "",
        "aws_secret_key": "",
        "aws_subnet_id": ""
    }
    "builders": {
        {
            "type": "amazon-ebs",
            "access_key": "{{user `aws_access_key`}}",
            "secret_key": "{{user `aws_secret_key`}}",
            "region": "us-east-1",
            "subnet_id": "{{user `aws_subnet_id`}}",
            "source_ami_filter": {
                "filters": {
                    "virtualization-type": "hvm",
                    "name": "ubuntu/images/*ubuntu-focal-20.04-amd64-server-*",
                    "root-device-type": "ebs"
                },
                "owners": ["099720109477"],
                "most_recent": true
            },
            "security_group_filter": {
                "filters": {
                    "tag:Class": "packer"
                }
            }
            "instance_type": "t2.micro",
            "ssh_username": "ubuntu",
            "ami_name": "ubuntu-ami-test_{{timestamp}}"
        }
    }
    "provisioners": {
        {
            "type": "shell",
            "script": "./init.sh"
        }
    }
}

Challenge

Adjust Structural Errors

The provided template has builders and provisioners provided as objects when they should be arrays. Switch the brackets for these overall components:

{
    "variables": {
        "aws_access_key": "",
        "aws_secret_key": "",
        "aws_subnet_id": ""
    }
    "builders": [
        {
            "type": "amazon-ebs",
            "access_key": "{{user `aws_access_key`}}",
            "secret_key": "{{user `aws_secret_key`}}",
            "region": "us-east-1",
            "subnet_id": "{{user `aws_subnet_id`}}",
            "source_ami_filter": {
                "filters": {
                    "virtualization-type": "hvm",
                    "name": "ubuntu/images/*ubuntu-focal-20.04-amd64-server-*",
                    "root-device-type": "ebs"
                },
                "owners": ["099720109477"],
                "most_recent": true
            },
            "security_group_filter": {
                "filters": {
                    "tag:Class": "packer"
                }
            }
            "instance_type": "t2.micro",
            "ssh_username": "ubuntu",
            "ami_name": "ubuntu-ami-test_{{timestamp}}"
        }
    ]
    "provisioners": [
        {
            "type": "shell",
            "script": "./init.sh"
        }
    ]
}

Finally, fix any missing commas:

{
    "variables": {
        "aws_access_key": "",
        "aws_secret_key": "",
        "aws_subnet_id": ""
    },
    "builders": [
        {
            "type": "amazon-ebs",
            "access_key": "{{user `aws_access_key`}}",
            "secret_key": "{{user `aws_secret_key`}}",
            "region": "us-east-1",
            "subnet_id": "{{user `aws_subnet_id`}}",
            "source_ami_filter": {
                "filters": {
                    "virtualization-type": "hvm",
                    "name": "ubuntu/images/*ubuntu-focal-20.04-amd64-server-*",
                    "root-device-type": "ebs"
                },
                "owners": ["099720109477"],
                "most_recent": true
            },
            "security_group_filter": {
                "filters": {
                    "tag:Class": "packer"
                }
            },
            "instance_type": "t2.micro",
            "ssh_username": "ubuntu",
            "ami_name": "ubuntu-ami-test_{{timestamp}}"
        }
    ],
    "provisioners": [
        {
            "type": "shell",
            "script": "./init.sh"
        }
    ]
}

Challenge

Run the Build
1. Using the credentials on the hands-on lab page, update the variables to use the provided access key, secret key, and subnet ID.
2. Save and exit the file.
3. Validate the template:
  
  packer validate ami-test.json
4. Run the build:
  
  packer build ami-test.json

About the author

Pluralsight Skills

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