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Packer by HashiCorp is an open-source tool that automates the creation of machine images for various platforms—AWS, Azure, Docker, and more—using a single source configuration. Instead of manually configuring each virtual machine or container, Packer enables you to bake your desired packages, dependencies, and application code into a golden image that’s ready for deployment.
The image illustrates how Packer creates images for AWS, Azure, and Docker, showing the flow from source to deployment.

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Key Benefits of Packer

  • Consistency: Build identical images every time.
  • Speed: Automate provisioning and eliminate manual steps.
  • Portability: Use a single HCL template across multiple cloud and container platforms.
  • Scalability: Integrate into CI/CD pipelines for fully automated image builds.
Before you begin, ensure you have the latest Packer CLI installed and your cloud provider credentials configured (AWS_ACCESS_KEY_ID, AWS_SECRET_ACCESS_KEY, etc.).

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Packer Configuration Components

A typical Packer template consists of three primary sections:
ComponentPurposeExample
BuildersDefines the target platform and base image (e.g., AWS AMI, Azure Managed Image, Docker).source "amazon-ebs" "ubuntu" { ... }
ProvisionersRuns scripts or commands to install dependencies, copy code, and configure services.provisioner "shell" { inline = ["sudo apt install nginx"] }
Post-ProcessorsOptional steps to compress artifacts, upload images to registries, or tag images.post-processor "docker-tag" { ... }

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Example: Building an Ubuntu AMI with Nginx

Below is a simple HCL template (template.pkr.hcl) that launches an EC2 instance from an Ubuntu AMI, installs Nginx, clones application code, and then creates a new AMI. 
source "amazon-ebs" "ubuntu" {
  ami_name      = "my-first-packer-image"
  instance_type = "t2.micro"
  region        = "us-east-1"
  source_ami    = "ami-0557a15b87f6559cf"
  ssh_username  = "ubuntu"
}

build {
  name    = "ubuntu-nginx-image"
  sources = ["source.amazon-ebs.ubuntu"]

  provisioner "shell" {
    inline = [
      "sudo apt update -y",
      "sudo apt install nginx -y",
      "git clone https://github.com/example/my-app.git /home/ubuntu/app",
      "sudo ufw allow 'Nginx HTTP'",
      "sudo systemctl enable nginx",
      "sudo systemctl start nginx"
    ]
  }
}

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Build Commands

Run these commands in your project directory: 
# Initialize the working directory
packer init .

# Validate the template syntax
packer validate template.pkr.hcl

# Build the image
packer build template.pkr.hcl

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How Packer Executes Builds

Packer processes your template in three sequential stages:
StageDescription
BuilderLaunches a temporary VM or container from the specified base image (e.g., spins up an EC2).
ProvisionerCustomizes the instance: installs packages, copies code, configures services, and runs scripts.
Post-ProcessorPackages the instance into a final image (AMI, VHD, Docker image), uploads or tags artifacts.

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Next Steps & References

Once you’ve created your custom image, integrate it into your deployment pipelines or use it as the base for auto-scaling groups, Kubernetes clusters, or container workloads. Links and further reading:

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