Tuesday, May 21, 2019

Intro to Packer

Packer is an opensource tool developed by HashiCorp to create machine images for multiple cloud platforms like AWS, GCP, Azure or even VMWare. As the name suggests it packs all your software, packages, configurations while baking your machine images. Perhaps Packer is the only tool right now in the market which solely focuses on creating machine images and giving us the ability to automate the machine image creation process.
In this blog post, we will learn What Packer does and how it does things. Sounds Interesting!!!!

What is Packer and Machine Images

"Packer can be used to creating identical machine images for multiple platforms from a single source configuration. Packer is lightweight, runs on every major operating system, and is highly performant, creating machine images for multiple platforms in parallel." 
https://www.packer.io/intro/ 
It does installs and configures the software by using different SCM tools such as Ansible, Chef or Puppet, shell scripts within your Packer-made images. You can either include your scripts in json template itself or you can source it from a file.

"A machine image is a single static unit that contains a pre-configured operating system and installed software which is used to quickly create new running machines. Machine image formats change for each platform. Some examples include AMIs for EC2, VMDK/VMX files for VMware, OVF exports for VirtualBox, etc"
https://www.packer.io/intro/ 

Why the Heck We Should Consider to Learn Packer!!!!!!!!

Consider a couple of scenarios mentioned below:-

Scenario1

If you want to have an immutable infrastructure in place. The key guideline behind an immutable infrastructure is that you never modify a running server. If a change is required, you instead completely replace the server with a new instance that contains the update or change.
The new server instance is created with an origin image that is built upon or a restored image from a previously defined server state. Version control and tag your images for easy rollback and distribution. Image contains all the application code, runtime dependencies, and configuration–in essence, the state needed for the software to run as expected. You will want to minimize the time required to bake all your required stuff into your image which can be achieved if you have proper tag maintained over your previous release images which can be used as an origin-golden image to bake the new image. The entire process of baking and using images become outstandingly easy by using Packer.

Scenario2

If you have autoscaling in place, there must be a requirement to scale up a new serviceable VMs as soon as possible but there are some concerns which spoil your expectations of serviceable VMs in the least time:
  • OS boot 
  • OS configuration 
  • SCM with Ansible or Chef 
  • Setting up your application
With having a pre-baked image in place, your time to scale up your VMs will drastically decrease.

So How Does Packer Works!!!!!!!!

Packer uses the JSON file as a template, it takes template as in input rolls up a temporary VMs based on the details provided, does the required configuration and stops it. After stopping the VMs it starts creating the image and save it as the name/tag provided in the template.
 
json file packer engine EC2 AMI
              
                                                       
Basic Concepts of Packer

There are two things which you will need to know to get started with packer:
  • Templates 
  • Commands

Templates

There are four sections in the Packer template: 
  • Variables(optional)-is an object of one or more key/value strings that define user variables contained in the template. If it is not specified, then no variables are defined 
  • Builders(required)- is an array of one or more objects that defines the builders that will be used to create machine images for this template, and configures each of those builders. 
  • Provisioners(optional)- is an array of one or more objects that defines the provisioners that will be used to install and configure the software for the machines created by each of the builders 
  • post-processors(optional)-  is an array of one or more objects that defines the various post-processing steps to take with the built images. If not specified, then no post-processing will be done
Sub-Commands

Likewise, Unix packer also takes subcommand and options. There are three sub-commands:
  • build-The packer build command takes a template and runs all the builds within it in order to generate a set of artefacts. The various builds specified within a template are executed in parallel unless otherwise specified. And the artefacts that are created will be outputted at the end of the build. 
  • validate- The packer validate command is used to validate the syntax and configuration of a template. The command will return a zero exit status on success, and a non-zero exit status on failure. Additionally, if a template doesn't validate, any error messages will be outputted. 
  • inspect -The packer inspect takes a template and outputs the various components a template defines. This can help you quickly learn about a template without having to dive into the JSON itself. The command will tell you things like what variables a template accepts, the builders it defines, the provisioners it defines and the order they'll run, and more.
Hope this blog helps you understand the basics of Packer. Having covered all the basics understanding, we can now "Get Started With Packer".

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