Automation with Hashicorp Packer #11: User Variables

Introduction

In this tutorial, we will explore how to utilize user-defined variables in Hashicorp Packer. Packer is a powerful tool that enables automation in creating custom images across various platforms such as AWS, Azure, GCP, VMware, Docker, Vagrant, and OpenStack. Understanding how to implement user variables can enhance the flexibility and reusability of your Packer templates.

Step 1: Define User Variables

User variables allow you to customize your Packer build configurations. You define these variables in your Packer template file.

1. Open your Packer template JSON file.
2. Add the variables section at the beginning of the file:

   {
     "variables": {
       "variable_name": "default_value"
     }
   }
   

3. Replace variable_name with a meaningful name and default_value with a value you want to assign.

Step 2: Use Variables in Packer Builders

Once defined, you can use these variables in your builders.

1. In the builders section, reference the variable using the syntax {{user variable_name}}.
2. Example:

   "builders": [
     {
       "type": "amazon-ebs",
       "access_key": "{{user `access_key`}}",
       "secret_key": "{{user `secret_key`}}",
       "region": "{{user `region`}}"
     }
   ]
   

Step 3: Pass Variables at Runtime

You can override the default values of your user variables when you run Packer.

1. Use the -var flag to set variables in the command line:

   packer build -var 'access_key=YOUR_ACCESS_KEY' -var 'secret_key=YOUR_SECRET_KEY' your_template.json
   

2. Alternatively, use a variables file (.pkrvars.hcl) to manage multiple variables:

   access_key = "YOUR_ACCESS_KEY"
   secret_key = "YOUR_SECRET_KEY"
   

Step 4: Validate Your Template

Before running the build, it’s a good practice to validate your Packer template.

1. Run the following command to check for syntax errors:

   packer validate your_template.json
   

2. Ensure no errors are returned before proceeding.

Step 5: Build the Image

Now that you have set up your user variables and validated your template, you can build your custom image.

1. Execute the build command:

   packer build your_template.json
   

2. Monitor the output for any errors or warnings during the build process.

Conclusion

Using user-defined variables in Hashicorp Packer enhances the customization and reusability of your image creation process. By defining variables, utilizing them in your builders, and passing them at runtime, you can create more flexible Packer templates. As a next step, consider exploring how to manage and version control your templates using external variable files for better organization. Happy packing!