What is Packer?
Packer is an open source tool for creating identical machine images for multiple platforms from a single source configuration. Packer does not replace configuration management like Chef or Puppet. In fact, when building images, Packer is able to use tools like Chef or Puppet to install software onto the image.
Advantage
Super fast infrastructure deployment. Packer images allow you to launch completely provisioned and configured machines in seconds, rather than several minutes or hours. This benefits not only production, but development as well, since development virtual machines can also be launched in seconds, without waiting for a typically much longer provisioning time.
Multi-provider portability. Because Packer creates identical images for multiple platforms, you can run production in AWS, staging/QA in a private cloud like OpenStack, and development in desktop virtualization solutions such as VMware or VirtualBox. Each environment is running an identical machine image, giving ultimate portability.
Improved stability. Packer installs and configures all the software for a machine at the time the image is built. If there are bugs in these scripts, they'll be caught early, rather than several minutes after a machine is launched.
Greater testability. After a machine image is built, that machine image can be quickly launched and smoke tested to verify that things appear to be working. If they are, you can be confident that any other machines launched from that image will function properly.
Builders
Builders are responsible for creating machines and generating images from them for various platforms. For example, there are separate builders for EC2, VMware, VirtualBox, etc. Packer comes with many builders by default, and can also be extended to add new builders.
The Template
The configuration file used to define what image we want built and how is called a template in Packer terminology. The format of a template is simple JSON.
Shell Provisioner
Type: shell
The shell Packer provisioner provisions machines built by Packer using shell scripts. Shell provisioning is the easiest way to get software installed and configured on a machine.
https://www.packer.io/docs/provisioners/shell.html
Template Engine
All strings within templates are processed by a common Packer templating engine, where variables and functions can be used to modify the value of a configuration parameter at runtime.
The syntax of templates uses the following conventions:
- Anything template related happens within double-braces:
{{ }}. - Functions are specified directly within the braces, such as
{{timestamp}}. - Template variables are prefixed with a period and capitalized, such as
{{.Variable}}.