Tuesday, May 21, 2019

Lets Get Started With Packer

In this blogpost, we will see how to get started with packer. We will cover installation, writing a template for creating AWS AMI. To get the basic understanding of how packer works, You can refer to our previous blog "Intro To Packer".
  Installation  
  1. Official method to download packer as precompiled binary, packer does not provide system packages and neither they have any plan to make it avail as such:-$curl -L https://releases.hashicorp.com/packer/1.4.0/packer_1.4.0_linux_amd64.zip
  2. After downloading the binary unzip it to the location you want to keep it. If you want it to be installed such that it can be used by system-wide users, do  not unzip in user space $sudo unzip packer_1.4.0_linux_amd64.zip -d /usr/local/packer 
  3. After unzipping the package, the directory should contain a single binary program called packer . 
  4. The final step to installation is to make sure the directory you installed Packer to is set on the PATH, so that it can be used using a command line. Open the /etc/environment and append the below line to the end of the file export PATH="$PATH:/usr/local/packer" After adding the line into the file to let the change reflect source the environment file $source /etc/environment 
  5. Verify the installation by firing packer command or simply check its version by    $packer --version . You should see the version of packer as an output.
Once installed, running packer is as simple as packer build <build-file>, which will take the build-file and run the steps we provide within. Let’s get started with a simple build file.

Setting Up Stage

                                                                                                                         
As we are building an image for AWS cloud, there are certain prerequisites which need to be taken care of.
You should have IAM user who has access to create and destroy ec2 instance, create an AMI, create and destroy security groups etc. You can find sample IAM policy for packer user in sample minimum IAM user policy for Packer.

After setting up your IAM user for packer, generate the access key and id and save it.
Now having noted the key, you can either directly use it in your template (which is not suggested) or you can configure it as an environment variable or the AWS CLI config on which you have the packer installed.

I have configured it with AWS CLI config so I did not have to define in variable section or in the builder section. You can also pass your access keys as variable as an option while running packer build command.
Here we will be installing apache webserver in the image. I have named this json file as httpd.json and used httpd.sh script to install httpd under provisioner section.


Below is the sample httpd.json file

{
   "variables": {
     "ami_id": "ami-0a574895390037a62",
     "app_name": "httpd"
   },

   "builders": [{
     "type": "amazon-ebs",
     "region": "ap-south-1",
     "vpc_id": "vpc-df95d4b7",
     "subnet_id": "subnet-175b2d7f",
     "source_ami": "{{user `ami_id`}}",
     "instance_type": "t2.micro",
     "ssh_username": "ubuntu",
     "ami_name": "PACKER-DEMO-{{user `app_name` }}",
     "tags": {
         "Name": "PACKER-DEMO-{{user `app_name` }}",
         "Env": "DEMO"

       }
   }],

  "provisioners": [
   {
       "type": "shell",
       "script": "httpd.sh"
    }
  ]

}

Below is the simple httpd.sh

#!/bin/bash


sudo apt-get update
sudo apt-get install -y httpd

First Validate your template by firing below command:-
packer validate httpd.json

You should get the output as a success, or as an error indicating the line number.

Now run packer build to build your image:-

packer build httpd.json

After a successful build, you will get AMI id as output and success message.

==> amazon-ebs: Prevalidating AMI Name: PACKER-DEMO-httpd
   amazon-ebs: Found Image ID: ami-0a574895390037a62
==> amazon-ebs: Creating temporary keypair: packer_5cd559df-84ce-ff8a-fa93-0c4477d988e4
==> amazon-ebs: Creating temporary security group for this instance: packer_5cd559e2-ea81-be15-b94a-c28493c0d3ff
==> amazon-ebs: Authorizing access to port 22 from [0.0.0.0/0] in the temporary security groups...
==> amazon-ebs: Launching a source AWS instance...
==> amazon-ebs: Adding tags to source instance
   amazon-ebs: Adding tag: "Name": "Packer Builder"
   amazon-ebs: Instance ID: i-06ed051a3435865c4
==> amazon-ebs: Waiting for instance (i-06ed051a3435865c4) to become ready...
==> amazon-ebs: Using ssh communicator to connect: *.*.*.*
==> amazon-ebs: Waiting for SSH to become available...
==> amazon-ebs: Connected to SSH!
==> amazon-ebs: Stopping the source instance...
   amazon-ebs: Stopping instance
==> amazon-ebs: Waiting for the instance to stop...
==> amazon-ebs: Creating AMI PACKER-DEMO-httpd from instance i-06ed051a3435865c4
   amazon-ebs: AMI: ami-0ce41081a3b649374
==> amazon-ebs: Waiting for AMI to become ready...
==> amazon-ebs: Adding tags to AMI (ami------)...
==> amazon-ebs: Tagging snapshot: snap-0ee3ce80ec289ed24
==> amazon-ebs: Creating AMI tags
   amazon-ebs: Adding tag: "Name": "PACKER-DEMO-httpd"
   amazon-ebs: Adding tag: "Env": "DEMO"
==> amazon-ebs: Creating snapshot tags
==> amazon-ebs: Terminating the source AWS instance...
==> amazon-ebs: Cleaning up any extra volumes...
==> amazon-ebs: No volumes to clean up, skipping
==> amazon-ebs: Deleting temporary security group...
==> amazon-ebs: Deleting temporary keypair...
Build 'amazon-ebs' finished.

==> Builds finished. The artifacts of successful builds are:
--> amazon-ebs: AMIs were created:
ap-south-1: ami--------------------

Few things to keep in mind:-

  • Packer does not create the image of any running instance, instead, it spins a temporary instance and create the image, post image creation it destroys all the resources which were created by a packer in order to create images. 
  • Though packer gives us ease of taking machine AMI’s programmatically, purging of an older image should also be kept in mind because AMIs gets stored over s3 and it might add up to your cost. 
  • Though a rollback becomes a lot easier in immutable infra. It can become a pain in the neck if you frequently make changes in production. 
  • We cannot expect it to solve all our problems, its only job is to create an image. You will have to decide when to create an image and what post action needs to be taken or deployed after image creation.

I hope the above setup will help you in getting started with it. Later we will discuss how we can use it along with Ansible and Terraform to achieve immutable Infra.
I appreciate any suggestions and comments or any questions/doubts faced while implementing it.

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".

Lets Get Started With Packer

In this blogpost, we will see how to get started with packer. We will cover installation, writing a template for creating AWS AMI. To get t...